N,N-Dimethylformamide Electrolyte Additive Via a ... - ACS Publications

Subscriber access provided by LUNDS UNIV

C: Energy Conversion and Storage; Energy and Charge Transport

N, N-Dimethylformamide Electrolyte Additive via a Blocking Strategy Enables High Performance Lithium Ion Battery Under High Temperature Lei You, Kaijia Duan, Ganbing Zhang, Wei Song, Tao Yang, Xin Song, Shiquan Wang, and Jianwen Liu J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b01387 • Publication Date (Web): 20 Feb 2019 Downloaded from http://pubs.acs.org on February 21, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

N,N-Dimethylformamide

Electrolyte

Additive

Via

a

Blocking Strategy Enables High Performance Lithium Ion Battery under High Temperature

Lei You

a,#

, Kaijia Duan

a,#

, Ganbing Zhang a, Wei Song a, Tao Yang

b,*

, Xin Song a,

Shiquan Wang a, Jianwen Liu a,*

a

Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials

& Ministry of Educational Key Laboratory for the Synthesis and Application of OrganicFunctional, Molecules & College of Chemistry and Chemical Engineering, Hubei University, Wuhan, 430062, China b

College of Materials & Environmental Engineering, Hangzhou Dianzi University,

Hangzhou, 310036, China

#

These authors contributed equally to this work.

*

Corresponding author: Dr. & Prof. Jianwen Liu. E-mail: [email protected] Dr. Tao Yang. E-mail: [email protected]

1

ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT: Currently adding suitable additive in the electrolyte is one of the most effective strategies to improve the electrochemical performance for lithium ion battery, especially under high temperature. In this work, N, N-dimethylformamide (DMF) as an electrolyte additive was introduced to improve battery performance of LiFePO4 at 60 oC. The addition of DMF can effectively increase the specific capacity, the cycling performance and rate performance of the batteries using LiFePO4 as cathode materials. The XRD results reveal that the electrode cycled in the electrolyte without additive appears Fe2O3, FePO4 and other impurity peaks under high temperature. SEM/TEM results indicate that some deposits are generated on the electrode surface without additive under high temperature due to the decomposition of electrolyte, the reaction between electrolyte and electrode materials. The FTIR/NMR/XPS results demonstrate that DMF as a lewis base can capture lewis acidic PF5 from the decomposition of LiPF6 as well as block the chain reaction of LiFePO4 with HF, which alleviate the electrolyte decomposition and electrode dissolution at high temperature. KEYWORDS: N, N-dimethylformamide; Lithium ion battery; Electrolyte additive; High temperature



INTRODUCTION

In recent years extensive attention on the rechargeable lithium-ion batteries (LIBs) has been attracted along with the swelling requirements of portable electronic devices, electric vehicles (EVs) and hybrid electric vehicles (HEVs). Compared with the

2


Page 2 of 33

Page 3 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


traditional lead-acid/nickel-cadmium batteries, LIBs have been widely used for EVs/HEVs owing to their high energy density, high voltage, light weight, low self-discharge and long cycle life. 1-8 However, large-scale energy applications require better LIBs with excellent environmental adaptability and high energy density compared with LIBs in portable electronic devices. When used for EVs/HEVs at ambient temperature, the internal temperature of LIBs will exceed 60 °C, and the temperature of electrolyte will be much higher, which may be aggravated by high-pulse cycling for high-power batteries in the application of EVs and HEVs. 9,10 Therefore, with the development of EVs/HEVs, higher requirements are put forward for the performance of LIBs in extreme environments, especially under high temperature conditions. As is known to all, the commercial electrolytes for LIBs are prepared by dissolving LiPF6 into organic carbonate including dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethylene carbonate (EC). The LiPF6-based electrolytes have poor thermal stability because of the decomposition of LiPF6 on the electrode’s surface at high voltage and elevated temperature during charge/discharge process, leading to the release of PF5 from decomposition of LiFP6. The product of PF5 can be rapidly reacted with trace protic impurities (ROH or H2O) in the electrolyte to form HF and POF3, which further accelerates the decomposition of the electrolyte.

11,12

The

reaction equation can be explained as follows: LiPF6 → LiF + PF5; PF5 + ROH (H2O) →HF + RF + OPF3. Therefore, there still exist several problems in practical application for LIBs, prompting the urgency of LIBs’ development. Among them,

3



Page 4 of 33

different electrolyte formulas or additives are significantly related to the safety performance of the batteries especially in some extreme environment, which is particularly important for the development of EVs/HEVs. Among various cathode materials of lithium ion batteries, lithium iron phosphate (LiFePO4) is considered as a potential cathode material for large scale application in EVs/HEVs.

13-16

However, LiFePO4 has poor thermal stability at high temperature,

resulting in the unsatisfactory cycle performance of the battery. In addition, the decomposition product of electrolyte, hydrogen fluoride (HF), can induce severe dissolution for LiFePO4, which is detrimental for the sustainable utilization of the battery. 17-22 Thus, to suppress the electrolyte decomposition and decrease the adverse impact from the electrolyte decomposition to the electrode, adding suitable additive is one of the most effective strategies. Many studies have reported that different additives can effectively improve the electrolyte performance and electrochemical properties of the LIBs at elevated temperature.

23-29

Wongittharom et al. have proposed three additives vinylene

carbonate (VC), γ-butyrolactone(γ-BL) and propylene carbonate (PC) adding in the ionic liquid (IL). It was testified that the performance of single IL electrolyte at 75 oC was superior to that in conventional organic electrolytes.

30

Li et al. added

prop-1-ene-1,3-sultone (PES) to LiPF6 in EC/DMC electrolyte solution, exhibiting high capacity retention of 82.3 mAhg-1 after 150 cycles at 60 oC for batteries.

31

Moreover, 0.5 wt.% lithium 4-pyridyl trimethyl borate (LPTB) was introduced as an additive by Xu et al and displayed good cycle performance of high-voltage at 55 oC

4


Page 5 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and better rate performance at -20 oC for batteries.

32

Chang et al. have reported

triphenyl borate (TPB) and trimethyl borate (TMB) as additives facilitating the performance of LiFePO4 batteries. The batteries with 0.1 M TPB only exhibited 7% capacity retention after 100 cycles at 60 oC, much less than that with 0.1 M TMB (53%). Chang have also recommended a novel electrolyte of 30 wt.% ionic liquid Triethylmethylammonium bis(trifluoromethylsulfonyl)imide (N1222-TFSI) mixed with 70 wt.% commercial carbonate electrolytes. This electrolyte had the properties of flame retardant, thermal stability, reducing the corrosion of Al and improving the battery performance at 25 and 60 oC.

33,34

CsPF6 as a wide-temperature electrolyte

additive was systematically investigated with the electrolyte’s ionic conductivity and phase-transition behaviours at different temperature by Li et al. The cells had high capacity retention from -40 to 60 oC.

35

In addition, 0.5 wt.% dimethyl phenyl

phosphate (DMPP) as additive produced a capacity improvement from 16% to 82% at 55 oC for LiMn2O4 after 200 cycles by Zhu et al.

36

1 wt.% tris(trimethylsilyl) borate

(TMSB) as additive showed a high discharge capacity retention and good cycle performance at 30 and 55 oC by Cai et al. 37 In order to compare their advantages and disadvantages of reported additives in literatures, Table S1 in the supporting information summarizes the electrochemical performances of additives used at high or low temperature for LIBs in recent years. As can be seen from the table, these additives reported in the literatures are all generally complex in the molecular structures and difficult to prepare, and some additives are poorly soluble, expensive and inherently toxic. Moreover, the current

5



Page 6 of 33

research on high-temperature electrolyte additives for LIBs was mainly focused on the electrochemical tests, however the explanation of mechanism and theoretical calculation were seldom introduced. Herein in our work, we have proposed N, N-dimethylformamide (DMF) as a novel additive to improve the thermal stability for the carbonate electrolyte at elevated temperature for the first time. DMF is a transparent liquid that can be easily and cheaply prepared, and miscible with water and most organic solvents. In this work, we added a small amount of DMF (1%-3%, by weight) as additive in base electrolyte of 1.0 M LiPF6 solution in EC/DMC/DEC (1:1:1, by weight). The electrochemical tests and characterization techniques were carried out to take verification and mechanism analysis of DMF as additive in LiFePO4

batteries.

Electrochemical

performance,

cycling

behaviour

and

electrochemical impedance spectroscopy (EIS) were tested in the electrolyte with and without DMF at elevated temperatures. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM)/ Transmission electron microscope (TEM), Fourier Transform infrared spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR,

31

P and

19

F) before and after discharge were also

investigated.



EXPERIMENTAL SECTION

DMF (purity: 99.5%) was purchased from Tianinfuyu Fine Chemical Co., Ltd, China and dehydrated by 4 Å molecular sieves before used. PVDF and NMP were purchased from Taiyuan Lizhiyuan Chemical Co., Ltd, China. The base electrolyte with 1.0 M

6


Page 7 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


LiPF6 solution in EC/DMC/DEC (1:1:1, by weight) and LiFePO4 materials were provided by Hubei Nuobang Chemical Company Co, Ltd. All the electrolytes were prepared in a highly pure argon-filled glove box in which water and oxygen contents were both controlled less than 0.1 ppm. The base electrolytes were divided into four bottles and DMF was added into different bottles labeled as E0 (0 wt.%), E1 (1 wt.%), E2 (2 wt.%) and E3 (3 wt.%), respectively. The photographs of electrolyte samples with different concentrations of DMF additive can be observed in the inset of Figure S1a in the supporting information. The electrolytes with different concentration additives are all colorless and transparent without any precipitation after stored for 5 months. All calculations were performed using the Gaussian 09 package. The equilibrium structures were optimized with the B3LYP in conjunction with the M06-2x/6-311++G(d,p) level basis set. At the same level, frequency calculations were also performed to confirm all optimized molecules with a consistent stationary. The calculated oxidation potential was converted from the free-energy cycle for the oxidation reaction. Detailed information about materials characterization and electrochemical measurements can be found in the Supporting Information.



RESULTS AND DISCUSSION

Figure S1a and S1b in the supporting information show the charge-discharge profiles and cycle performance of Li/LiFePO4 batteries at 25 oC in the different

7



electrolyte E0, E1, E2, E3, respectively. As can be seen, the capacity of the battery with E0 electrolyte has a slight loss from 150 mAh·g-1 to 148 mAh·g-1, a capacity retention of 98% after 100 charge-discharge cycles. Meanwhile the capacity retentions of batteries with electrolytes E2 and E3 are 93% and 79% respectively, while battery with electrolyte E1 hardly has a capacity attenuation with an almost 99% capacity retention. In the cyclic voltammetry (CV) curves, the initial CV curves of batteries in the electrolyte E0, E1 and E2 can be seen in Figure S1c and S1d in the supporting information. E0 and E1 have the same peaks of oxidation at 3.6 V and reduction at 3.3 V (both vs. Li+/Li), which are ascribed to the same redox reaction of Fe3+/Fe2+. Moreover, no other redox peaks are found on the CV curves, indicating that the addition of DMF does not lead to the existence of a new redox system, which are beneficial for battery performance at room temperature. Based on the above battery performance and CV results, therefore, the following research will take 1 wt.% DMF as the research objectives. The charge and discharge curves of half battery (vs Li/Li+) in the electrolyte without and with DMF additive under high temperature can be observed in Figure 1a and 1b. In the first 50 cycles, charge and discharge performance remain stable regardless of the addition of additive, indicating that in the early stages of battery cycle under high temperature, the electrode materials have not been eroded and destroyed, even high temperature can accelerate the transfer speed of lithium ion and maintain high utilization rate of lithium capacity. From

8


Page 8 of 33

Page 9 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the 50th cycle on, it is obvious that the battery charge capacity is far greater than the discharge capacity for the electrolyte without DMF additive, and this difference is further increased until 150 cycles. It must be pointed out that the electrochemical polarization of the battery during charge and discharge is aggravated in the high temperature environment, resulting in the severe loss of the battery capacity. This may also be due to increased irreversible capacity of the battery resulting from increased temperature and electrolyte decomposition. Figure 1c and 1d display the charge and discharge curves of full battery (vs graphite) in the electrolyte without and with DMF additive under high temperature. The charge and discharge trends appear much the same as the half battery (vs Li/Li+), that is, the capacity attenuation becomes severe in the electrolyte without DMF additive since the initial 50 cycles on. As represented in Figure 1e, the Li/LiFePO4 half battery with 1 wt.% DMF delivers superior discharge capacities of 163.3, 139.4, 117.5, 97.1 and 74.0 mAh.g-1 at 0.2, 0.5, 1, 2 and 5 C, respectively, which are all higher than 161.5, 132.9, 110.9, 81.5 and 41.4 mAh.g-1 for the Li/LiFePO4 electrodes without additive at corresponding current rates. It reveals that adding DMF is also beneficial for the high rate performance of the battery at high temperature. Figure 1f shows the comparison of battery cycle performance with and without additive at 60 oC. Before the 50 cycles no matter whether additive is added or not, the battery cycle capacity has basically no difference with the same capacity retention rate, close to 94%. However, from the 50 cycle on, the discharge capacity of the battery with no

9



additive begins to decay rapidly, and the capacity retention remains 73% at the 100 cycle, and the capacity remains only 58% at the 150 cycle. In contrast, the battery with additive also appears discharge capacity attenuation, but the attenuation trend is relatively mild, that is, the cycle capacity retention is maintained 86% at 100 cycle and 85% at 150 cycle respectively. The cycle performance of graphite/LiFePO4 full battery at 60 oC shown in Figure 1g and 1h indicates that the full battery in the electrolyte with DMF additive exhibits more stable cycling than that with no additive whatever at 0.2 C or 1 C. Figure S2a in the supporting information displays the comparison of battery coulombic performance with and without additive at 60 oC. Similarly, there is no difference between the batteries with and without additive before 50 cycles. Even the battery without additive shows better coulombic efficiency compared to the battery with additive. From the 50 cycle on, the coulombic efficiency of the battery without additive drops sharply. After 100 cycles, the coulombic efficiency of the battery decreases to 50%, and drops to nearly 10% when 150 cycles are reached.

10


Page 10 of 33

Page 11 of 33

(b)

3.2

1st 50th 100th 150th

2.8 2.4

0

100 200 300 400 500 -1 Specific Capacity (mA h g )

4.0

E0

3.6 3.2


2.8 2.4

0

40 80 120 -1 160 Specific Capacity (mA h g )

0.2C

1C 2C 5C

80 40

60 oC Half cell

E0 E1 0

(g)

5

10 15 20 25 Cycle numbers

30

120 80 40

E1 E0 60 oC; Full cell; 0.2 C

0 0

40 80 Cycle Numbers

120

Discharge Capacity (mA h g-1)

0.2C 0.5C

120

0

3.2


2.8 2.4

0

40 80 120 160 -1 Specific Capacity (mA h g )

E1

4.0 3.6 3.2


2.8 2.4

0

40 80 120 -1 Specific Capacity (mA h g )

160

(f) 160

60 oC; Half cell; 0.2 C

120 80

E1 E0

40 0

40 80 Cycle Numbers

(h) Discharge Capacity (mA h g-1)

160

3.6

(d)

(e) Discharge Capacity (mA h g-1)

E1

4.0

+

3.6

(c) Voltage (V vs Graphite)

Voltage (V vs Li/Li )

E0

4.0

Voltage (V vs Graphite)

Voltage (V vs Li/Li+)

(a)

Discharge Capacity (mA h g-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


120

100 80 60 E1 E0

40 20

60 oC; Full cell; 1 C

0 0

Figure 1. The charge/discharge profiles at 60

40 80 Cycle Numbers o

120

C of half battery in the

11



electrolyte (a) without and (b) with DMF additive, full battery (c) without and (d) with DMF additive at 1st, 50th, 100th, 150th cycles; (e) rate performance at 60 oC of half battery in the electrolyte with and without DMF additive from 0.2 to 5 C; the cycling performance at 60 oC of (f) half battery at 0.2 C, full battery at (g) 0.2 C and (h) 1 C.

In order to verify the cause of above performance, related theoretical calculation was first carried out using the Gaussian 09 package. Figure 2a presents the highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energies of DMF, with a comparison with solvents EC, DEC and DMC. Apparently, the HOMO energy of DMF (-0.30909 au.) is less negative than EC (-0.38411 au.), DEC (-0.37276 au.), and DMC (-0.37839 au.), revealing that DMF experiences preferential oxidation before the base electrolyte. It appears that the exclusive decomposition products from DMF oxidation leads to the formation of a stable interphase, as DMF has a lowest oxidation potential than EC, DEC and DMC, as shown in Figure S3 in the supporting information. To understand the mechanism of the improved thermal stability of the electrolyte, theoretical calculations on binding ability between the PF5 gas and DMF, solvents EC, DEC, DMC were performed. Figure 2b displays the calculated relative binding energy (ΔE) of the complexes of PF5 in the solution based on the reaction PF5 + S = PF5－S, where S represents solvents EC, DEC, DMC or DMF. The relative energies of PF5-EC, PF5-DEC,

12


Page 12 of 33

Page 13 of 33

PF5-DMC and PF5-DMF are -50.9, -60.6, -54.6 and -107.1 kJ.mol-1, respectively, suggesting the PF5-DMF are much more stable than PF5-EC, PF5-DEC and PF5-DMC.

HOMO (au.)

-0.30

(a) ♦ HOMO= -0.3091

-0.32

DMF

LUMO= -0.0092

-0.34 -0.36

♦

EC

-0.38

♦

-0.40

-0.015

(b)

♦

HOMO= -0.3784 DMC LUMO= -0.0014

-0.010 -0.005 LUMO (au.)

• ΔΕ (KJ mol-1)

HOMO= -0.3728 LUMO= -0.0027 DEC

HOMO= -0.3841 LUMO= -0.0139

More reactive

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


•

-60

0.000

•

-80 -100

• PF5-EC • PF5-DMC • PF5-DEC • PF5-DMF

•

Figure 2. (a) HOMO/LUMO energies (au.) and optimized structures of EC, DEC, DMC and DMF; (b) Relative energies and optimized structures of PF5-DMF, PF5-EC, PF5-DEC and PF5-DMC.

13



To ascertain the phase changes of electrode materials before and after cycles, XRD patterns can be observed in Figure 3. The characteristic diffraction peaks of LiFePO4 before and after the battery cycles are both displayed, for example at 21.2o, 26.1o, 29.8o, 35.5o, et al. 2-theta position. But it is obvious that the relative intensity of the characteristic diffraction peaks is weakened after 150 cycles, indicating that the crystal structure has been changed. Meanwhile the impurity peaks of LiF both appear in the electrode materials cycled in the electrolyte with and without additive, demonstrating that the decomposition of electrolyte cannot be avoided under high temperature, especially the LiF peak intensity of the electrode materials without additive is more notable. Moreover, the electrode material without additive obviously appears Fe2O3, FePO4 and other impurity peaks. It means that electrode materials without additive cannot be prevented from erosion and destruction under high temperature conditions, thus forming new impurity phases, which is extremely unfavourable for the battery cycle performance.

14


Page 14 of 33

(222) (402)

(112)

(311)

(020)

(111) (201)

(101)

Intensity (A.U.)

(a) (b) (c) (d) (e)

15

Fe2O3

20 25 30 35 2-Theta (Degree)

40

LiF

60

70

(222) (402)

(112)

(311)

(121) (410)

(301)

P2O5

40 50 2-Theta (Degree)

Intensity (A.U.)

FePO4

30 (020)

(210) (011) (111) (201)

(101)

20

(200)

10

Intensity (A.U.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(200)

Page 15 of 33

LiF

40 45 50 55 60 65 70 2-Theta (Degree)

Figure 3. XRD patterns of (a) pristine LiFePO4 and LiFePO4 cathodes after 150 cycles in the electrolytes (b) without DMF and (c-e) with DMF under the temperature of 60 oC.

From the SEM and TEM images of LiFePO4 cathodes after 150 cycles in the electrolytes without and with DMF additive shown in the Figure 4, the surface morphologies of the electrode materials with and without additive show

15



significantly different. There are some obvious solid deposits on the electrode surface without DMF additive, while no deposits can be observed on the electrode surface with DMF additive. These deposits can be visually identified as many disordered particle accumulations about 200-1000 nm (in Figure 4b and d). Formation of these deposits may be derived from the decomposition of electrolyte, the reaction between electrolyte and electrode material, which can be explained as schematic diagram of deposits on the LiFePO4 electrodes after cycles shown in Figure 4e. In comparison, a thin and uniform cathode electrolyte interfaces (CEI) of about 20 nm can be obviously observed for the electrode with DMF additive in Figure 4c, which can form a protective interface for the improved cycling stability under the temperature of 60 oC. In order to clearly convince the compositions of electrodes and deposits, the HRTEM and EDS images can be observed in the Figure S4 in the supporting information. The lattice structure can be calculated from lattice fringe through Digital-Micrograph software analysis. They are shown as 1.601 Å and 2.364 Å respectively in the images, corresponding to the (521) crystal surface of LiFePO4 and the (104) crystal surface of FePO4, which proves that the impurity deposits FePO4 were generated when cycled in the electrolyte without DMF additive. It is also obvious from the EDS results that the elements of Fe, O, P display uniform distribution in the electrode cycled in the electrolyte with DMF additive.

16


Page 16 of 33

Page 17 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(a)

(b)

No deposits

Deposits

1 μm

1 μm

(d)

(c)

Deposits

500 nm

20 nm

(e)

Adding DMF LiFePO4

No Adding LiFePO4

LiFePO4

Deposits

CEI film

Figure 4. SEM and TEM images of LiFePO4 cathodes after 150 cycles in the electrolytes (a,c) with DMF and (b,d) without DMF additive under the temperature of 60 oC; (e) Schematic diagram of CEI film and deposits on the LiFePO4 electrodes after cycles in the electrolytes with and without DMF additive.

To verify the impedance characteristics of the as-generated deposit interface,

17



the impedance performance of the battery was tested. Figure 5 presents the electrochemical impedance spectra before and after 150cycles when the cathodes from the spent batteries were disassembled and used to assemble fresh batteries for impedance testing. It is obvious that the resistance of electron transport Rct in the intermediate frequency region has much difference for the batteries without additive before and after the cycles whatever the half battery or full battery, the Rct value of the half battery without additive is increased from 161 Ω to 612 Ω, and from 126 Ω to 498 Ω for full battery, reflecting the increased electron transfer impedance and decreased electrochemical kinetic performance due to the as-generated deposits. Therefore, the intercalation and de-intercalation of lithium ion in the electrode material becomes more difficult. The decrease of the kinetic performance weakens the active materials involved in the discharge process, which makes lithium ions more difficult to diffuse from the electrode surface to the internal, greatly affecting the cycle performance of the battery. 38-40 However the Rct has no significant difference for the batteries with DMF additive before and after the cycles whatever the half battery or full battery. Figure S5 in the supporting information shows the photographs of electrolyte samples without and with DMF additive after stored under the temperature of 60 oC for 1 day and 7 days respectively. Obvious precipitation was observed in the base electrolyte without DMF after storage at high temperature for 7 days, while this phenomenon was not detected in the electrolyte with DMF additive. Additionally, the photographs of electrolyte with

18


Page 18 of 33

Page 19 of 33

and without DMF additive stored for 1 month and 6 months at room temperature can also be observed. It is obvious that there are both no deposits and precipitations in the electrolytes, which proves that the electrolyte with DMF additive can maintain long-term stability.

(c)

(a)

100

E0 E1

-Z'' (ohm)

60 oC; Half cell; 80 Before cycling

40 0 0

40

60 oC; Full cell; Before cycling

40

80 120 Z' (ohm)

160

200

0 0

E0 E1

60 oC; Half cell; After cycling

200

250

100

50 100 Z' (ohm)

(d)

300

300

0 0

60

20

(b) 400

E0 E1

80

-Z'' (ohm)

-Z'' (ohm)

120

-Z'' (ohm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


E0 E1

200

150

60 oC; Full cell; After cycling

150 100 50

200

400 Z' (ohm)

600

800

0 0

100

200 300 Z' (ohm)

400

500

Figure 5. Electrochemical impedance spectra of LiFePO4 (a, b) half battery and (c, d) full battery in the electrolytes with and without DMF additive before and after 150 cycles at 60 oC.

To further identify the chemical composition, element content and valence states of the electrode surface in the electrolytes with or without additive, the XPS measurements were performed after 150 cycles and the results was presented in the Figure 6. First as shown in Figure 6g and 6h, compared to the 19



Page 20 of 33

electrode in electrolyte without DMF additive, the concentrations of C, F, Fe, P and N increase, only the concentration of O decreases for the cycled LiFePO4 electrode in electrolyte with DMF additive. In the C1s spectra, four main peaks appear on the electrode in the electrolyte with or without additive, corresponding to hydrocarbons (C-H, C-C at 284.8 eV), C-O-C bonds (286-287 eV), C=O bonds (286.5 eV for R-CH2OCO2-Li and 288-290 eV for Li2CO3) and C-F2 from PVDF (291 eV), respectively.

41

The significant difference

mainly lies in the C=O peaks at 289.6 eV for Li2CO3, that is, the electrode without additive shows much stronger C=O peak. The O1s spectra are composed of three peaks belonging to C-O and C=O bonds (531.5 eV, 532.1 eV for Li2CO3) and C-O-P (532.8 eV), respectively.

42

Similarly, the electrode

without additive displays a little stronger C-O and C=O peaks from Li2CO3. As we know Li2CO3 is one of the main decomposition products of carbonate-based electrolyte,

therefore

the

addition

of

DMF

can

effectively

prevent

carbonate-based electrolyte decomposition. In the F1s spectra three main peaks can be seen: C-F2 from PVDF (688 eV), LixPOyFz (687 eV) and LiF (685.5 eV), and obviously the electrode without additive appear much higher peaks from F-O-P and LiF. LixPOyFz and LiF are the main by-products of electrolyte decomposition, once LixPOyFz and LiF are generated too much, the intercalation and de-intercalation of Li ion during charge and discharge will be seriously affected, mainly due to the poor conductivity and increased interface impedance.

43,44

These results reveal that the addition of additive inhibit the

20


Page 21 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


formation of the by-products and promote the transportation of Li ion in the electrolyte. The Fe2p spectra show much difference on iron content of electrodes, illustrating that the iron dissolution of electrode without additive is significant due to the erosion and dissolution of the electrode material under high temperature. Quantitative determination of the iron element was also carried out by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The cycled LiFePO4 electrodes were rinsed with dimethylacetamide (DMAC) and dissolved in 5 ml of 3% HNO3, and the solution was diluted to 20 mL for analysis. From Figure S6 in the Supporting Information the results show that the dissolution of iron is rather severe in the solution without additive, especially after 50 cycles. In the P2p spectra, the main peak is observed at 133.2 eV for P-O bond, which can be found it all in the three electrodes resulting from LiFePO4 materials. However, an additional peak only appears on electrode without additives at 136.7 eV for LixPOyFz and LixPFz, which are the decomposition by-products from LiPF6 and carbonic ester. This results also demonstrate that the formation of by-products is more severe under high temperature in base electrolyte than that in DMF-containing electrolyte. 45 Meanwhile, an obvious peak of C-N (400.3 eV) appears only on electrode with additives in N1s spectra, indicating that addition of DMF participate in the electrochemical reaction between electrolyte and electrodes.

21



(a) C1s

C=O

C-C,C-H

(b) F1s

C-O-C

E0

(c) Fe2p

F-P

C-F2

E1

E1

Fresh

(d) P2p

E0

E0

E1

E1

LiF

E0

P-O

Fresh

Fresh Fresh

C-O-C

292 290 288 286 284 282 692 690 688 686 684 Binding energy (eV) Binding energy (eV)

(e) O1s E0

C=O C-O

(f) N1s E1

534 532 530 528 Binding energy (eV)

Fresh E0 E1

40 20

E1 C-O-P 536

(g) 60

C-N



735 730 725 720 715 710 705 Binding energy (eV)

0

C

O Elements

F

Concentration (%)

C-F2

P-O P-F

C-F2

C-C,C-H

Concentration (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 33

(h)

Fresh E0 E1

3 2 1 0

P

Fe Elements

N

Figure 6. XPS spectra and concentrations of C, F, Fe, P, O, N of fresh LiFePO4 and LiFePO4 cathodes after 150 cycles in the electrolytes with and without DMF additive at 60 oC.

Further to say, the thermal decomposition products of the electrolytes with and without DMF additive before and after storage at 60 oC for 168 hours were analyzed through FTIR and NMR test. As presented in Figure S7 in the supporting information, the characteristic FTIR absorption peaks of DMF before and after storage at high temperature display no significant difference, indicating that the DMF itself maintains the basic stability. The FTIR absorption peaks of electrolyte with and without DMF additive before storage also display no much difference, revealing that the addition of DMF do not cause much change in composition or structure for electrolyte. In addition, many strong peaks located at 1805, 1744, 1658, 1490, 1400, 1302 cm-1 are mainly derived from carbonate solvents themselves (EC, DEC, DMC), 22


Page 23 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the reaction product between the solvents and electrolyte salts (Li2CO3, ROCO2Li), or the decomposition of electrolyte (LixPOyFz, LixPFy), etc (in Figure S6c and S6d). 31,36,44-48

Among them, LixPOyFz and LixPFy are the main by-products of electrolyte

decomposition, and other components are the main sources for the formation of electrode SEI film due to the electrolyte decomposition. In the presence of DMF, the FTIR spectra of the electrolyte before and after storage displayed no conspicuous difference. The peak centered at 1302 cm-1, corresponding to the characteristic of LixPOyFz was detected in the electrolyte without DMF, revealing that the side reactions of the electrolyte are significantly occurred at high temperature. In the

31

P

NMR spectra shown in Figure 7, the peaks at -130 ~ -160 ppm are attributed to the saturated phosphorus of PF6-, which can be all seen in the four NMR spectra. Only in the base electrolyte without DMF additive after storage at 60 oC, three small peaks are obvious to be observed. The peaks at -10 ~ -30 ppm labeled as i in the inset of Figure 7c represent the PO2F2- groups, which reveal that the base electrolyte is severely decomposed under the high temperature. The same results are also displayed in the 19

F NMR spectra shown in Figure 7g.

23



(a)

(b)

-

PF6

-40

(c)

-80 -120 δ (ppm)

-160

0

-40

-

-30

-30 -25 -20 -15 -10 δ (ppm)

(e) PF

-80 δ (ppm)

-120

-160

PF6

-

PF6

i

-40

-120

EC:DEC:DMC = 1:1:1 + 1 wt.% DMF o after storage at 60 C for 30 days

i

0

-80 δ (ppm)

(d)

EC:DEC:DMC = 1:1:1 after storage o at 60 C for 30 days

i

-

PF6 EC:DEC:DMC = 1:1:1 + 1 wt. % DMF

EC:DEC:DMC = 1:1:1

0

Page 24 of 33

0

-160

-20

-15

δ (ppm)

-40

(f) PF

-

6

-25

-10

-80 δ (ppm)

-120

-160

-

6

EC:DEC:DMC = 1:1:1 + 1 wt. % DMF

EC:DEC:DMC = 1:1:1

-80

-120 δ (ppm)

(g)

-160

-80

(h)

EC:DEC:DMC = 1:1:1 after storage o at 60 C for 30 days iii

-120 δ (ppm)

-160

EC:DEC:DMC = 1:1:1 + 1 wt.% DMF o after storage at 60 C for 30 days

-

PF6

-

ii

PF6

ii

-154

-155

δ (ppm)

-156

-80 -82 -84 -86 -88 δ (ppm)

-80

-120 δ (ppm)

-80

-160

24


-120 δ (ppm)

-160

Page 25 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. 31P NMR spectra of (a) base electrolyte and (b) electrolyte with DMF additive before storage and (c) base electrolyte and (d) electrolyte with DMF additive after storage at 60 oC (signal i is assigned to PO2F2-);

19

F NMR spectra of

(e) base electrolyte and (f) electrolyte with DMF additive before storage and (g) base electrolyte and (h) electrolyte with DMF additive after storage at 60 oC (signals ii and iii are assigned to PO2F2- and HF, respectively).

Based on the FTIR, NMR, XRD, XPS and SEM/TEM results and related calculation, the mechanism behind the electrolyte decomposition and changes is first described as the “blocking mechanism”, as shown in Figure 8. Firstly, the decomposition of LiPF6 on the electrode’s surface at elevated temperature can easily cause the generation of harmful gas PF5 and insulated LiF due to the poor thermal stability of traditional LiPF6-based electrolytes, as shown in the route (1). Then the as-generated PF5 can be rapidly reacted with trace protic impurities such as ROH or H2O in the electrolyte and subsequently to form by-products HF and POF3. POF3 will further accelerate the generation of by-products LixPOyFz and LixPOFy, while HF can constantly react with the intermediate product FePO4 during the intercalation/de-intercalation process, resulting in the formation of by-products Fe2O3 and FeF3, as shown in the route (2). Consequently, the electrode materials will be corroded and dissolved continuously. As shown in route (3), with the addition of DMF into the base electrolyte, the lewis base can rapidly capture the lewis acid PF5, therefore

25



effectively blocking the further occurrence of side reactions and the corrosion of electrode materials. It must be pointed out that the molecular of DMF with a pair lone electron can be integrated with the unelectronic structure of PF5 in the electrolyte, which can be defined as "blocking mechanism".

Figure 8. The blocking mechanism of DMF for decomposition of LiPF6, the generation of by-products, and dissolution of LiFePO4 electrode during charge and discharge.



CONCLUSIONS

A novel type of electrolyte additive DMF used at high temperature was proposed in this work. The addition of DMF can improve the storage properties of the electrolyte at high temperature, and meanwhile inhibit the decomposition of electrolyte during

26


Page 26 of 33

Page 27 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the high temperature cycle. The formation of CEI film derived from the addition of DMF is also beneficial to prevent the dissolution of lithium iron phosphate cathodes. These features allow the batteries to exhibit excellent cycle performance (125.8 mAh.g-1 after 150 cycles) and rate performance (74.0 mAh.g-1 at 5 C) at high temperature (60 oC). The "blocking mechanism" is also proposed based on theoretical calculations, where DMF as a lewis base can capture lewis acidic PF5 from the decomposition of LiPF6, therefore effectively blocking the occurrence of side reactions and the corrosion of electrode materials. The discovery of this DMF additive is of great significance for promoting the application of lithium ion batteries at high temperature in large scale applications.



ACKNOWLEDGEMENTS

The authors gratefully acknowledge the financial support from National Natural Science Foundation of China (No. 21706055). The authors would like to thank the Analytical and Testing Center of Hubei University for providing the facilities to fulfill the experimental measurements and Hubei Nuobang Chemical Company Co, Ltd for providing technical support. Meanwhile we also gratefully thank Professor Zaiping Guo from University of Wollongong for providing guidance and help for the experimental design and article writing.



SUPPORTING INFORMATION

Supplementary data associated with this article can be found in the online version.

27





REFERENCES

(1) Nitta, N.; Wu, F.; Lee, J.T.; Yushin, G. Li-ion battery materials: present and future. Mater. Today 2015, 18, 252-264. (2) Rodrigues, M.T.F.; Babu, G.; Gullapalli, H.; Kalaga, K.; Sayed, F.N.; Kato, K.; Joyner, J.; Ajayan, P.M. A materials perspective on Li-ion batteries at extreme temperatures. Nat. Energy 2017, 2, 2017108. (3) Etacheri, V.; Marom, R.; Ran, E.; Salitra, G.; Aurbach, D. Challenges in the development of advanced Li-ion Batteries: A review. Energ. Environ. Sci. 2011, 4, 3243-3262. (4) Lu, J.; Chen, Z.; Ma, Z.; Pan, F.; Curtiss, L.A.; Amine, K. The role of nanotechnology in the development of battery materials for electric vehicles. Nature Nanotech. 2017, 12, 90-95. (5) Zhang, X.; Cheng, F.; Yang, J.; Chen, J. LiNi0.5Mn1.5O4 porous nanorods as high-rate and long-life cathodes for Li-ion batteries. Nano Lett. 2013, 13, 2822-2825. (6) Sujith, K.; Moonsu, Y.; Minki, J.; Liu, H.K.; Dou, S.X.; Jaephil, C.; Guo, Z.P. Feasibility of cathode surface coating technology for high-energy lithium-ion and beyond-lithium-ion batteries. Adv. Mater. 2017, 29, 1605807. (7) Liu, J.Y.; Pang, W.K.; Zhou, T.; Chen, Long.; Wang, Y.G.; Vanessa, K.P.; Yang, Z.Q.; Guo, Z.P.; Xia, Y.Q. Li2TiSiO5: a low potential and large capacity Ti-based anode material for Li-ion batteries. Energ. Environ. Sci. 2017, 10, 1456-1464. (8) Liu, Y.J.; Tai, Z.X.; Zhou, T.F.; Sencadas, V.; Zhang, J.; Zhang, L.; Konstantinov, K.; Guo, Z.P.; Liu, H.K. An all-integrated anode via interlinked chemical bonding between double-shelled– yolk-structured silicon and binder for lithium-ion batteries. Adv. Mater. 2017, 29, 1703028. (9) Berckmans, G.; Messagie, M.; Smekens, J.; Omar, N.; Vanhaverbeke, L.; Mierlo, J.V. Cost projection of state of the art lithium-ion batteries for electric vehicles up to 2030. Energies 2017, 10, 1314-1323. (10) Scrosati, B.; Garche, J. Lithium batteries: status, prospects and future. J. Power Sources 2010, 195, 2419-2430. (11) Haregewoin, A.M.; Wotango, A.S.; Hwang, B.J. Electrolyte additives for lithium ion battery electrodes: progress and perspectives. Energ. Environ. Sci. 2016, 9, 1955-1988. 28


Page 28 of 33

Page 29 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(12) Wang, J.; Yuki, Y.; Keitaro, S.; Hua, C.C.; Yoshitaka, T.; Atsuo, Y. Superconcentrated electrolytes for a high-voltage lithium-ion battery. Nat. Commun. 2016, 7, 12032. (13) Kim, J.H.; Pieczonka, N.P.; Yang, L. Challenges and approaches for high-voltage spinel lithium-ion batteries. Chemphyschem 2014, 15, 1940-1954. (14) Yuan, L. X.; Wang, Z.H.; Zhang, W.X.; Hu, X.L.; Chen, J.T.; Huang, Y.H.; Goodenough, J.B. Development and challenge of LiFePO4 cathode materials for Li-ion batteries. Energ. Environ. Sci. 2011, 4, 269-284. (15) Wang, J.; Sun, X. Understanding and recent development of carbon coating on LiFePO4 cathode materials for lithium-ion batteries. Energ. Environ. Sci. 2012, 5, 5163-5185. (16) Li, W.; Song, B.; Manthiram, A. High-voltage positive electrode materials for lithium-ion batteries. Chem. Soc. Rev. 2017, 46, 3006-3059. (17) Osada, I.; De, V.H.; Scrosati, B.; Passerini, S. Ionic-liquid-based polymer electrolytes for battery applications. Angew. Chem. Int. Ed. 2016, 55, 500-513. (18) Liu, Y.H.; Takeda, S.; Kaneko, I.; Yoshitake, H.; Yanagida, M.; Saito, Y.; Sakai, T. An approach of evaluating the effect of vinylene carbonate additive on graphite anode for lithium ion battery at elevated temperature. Electrochem. Commun. 2015, 61, 70-73. (19) Song, X.; Tang, H.; Liang, C.; Long, H.L.; Zhou, L.; Song, W.; You, L.; Wu, Z.S.; Liu, J.W. Direct regeneration of cathode materials from spent lithium iron phosphate batteries using a solid phase sintering method. RSC Adv. 2017, 7, 4783-4790. (20) Safari, M.; Delacourt, C. Simulation-based analysis of aging phenomena in a commercial graphite/LiFePO4 cell. J. Electrochem. Soc. 2011, 158, A1436-A1447. (21) Lin, X.; Salari, M.; Arava, L.M.; Ajayan, P.M.; Grinstaff, M.W. High temperature electrical energy storage: advances, challenges, and frontiers. Chem. Soc. Rev. 2016, 45, 5848-5887. (22) Guo, Z.; Chen, Z.; High-temperature capacity fading mechanism for LiFePO4/graphite soft-packed cell without Fe dissolution. J. Electroanal. Chem. 2015, 754, 148-153. (23) Zheng, J.; Engelhard, M.H.; Mei, D.; Jiao, S.; Polzin, B.J.; Zhang, J.G.; Xu, W. Electrolyte additive enabled fast charging and stable cycling lithium metal batteries. Nat. Energy 2017, 2, 17012. (24) Kim, H.S.; Jurng, S.; Sim, S.; Yoon, T.; Mun, J.; Ji, H.R.; Oh, S.M. An azamacrocyclic electrolyte additive to suppress metal deposition in lithium-ion batteries. Electrochem. Commun. 29



2015, 58, 25-28. (25) Suo, L.; Borodin, O.; Gao, T.; Olguin, M.; Ho, J.; Fan, X.; Luo, C.; Wang, C.; Xu, K. "Water-in-salt" electrolyte enables high-voltage aqueous lithium-ion chemistries. Science 2015, 350, 938-943. (26) Miao, R.; Yang, J.; Xu, Z.; Wang, J.; Nuli, Y.; Sun, L. A new ether-based electrolyte for dendrite-free lithium-metal based rechargeable batteries. Sci. Rep. 2016, 6, 21771. (27) Kimura, K.; Yajima, M.; Tominaga, Y. A highly-concentrated poly(ethylene carbonate)-based electrolyte for all-solid-state Li battery working at room temperature. Electrochem. Commun. 2016, 66, 46-48. (28) Lécuyer, M.; Gaubicher, J.; Barrès, A.L.; Dolhem, F.; Deschamps, M.; Guyomard, D.; Poizot, P. A rechargeable lithium/quinone battery using a commercial polymer electrolyte. Electrochem. Commun. 2015, 55, 22-25. (29) Wang, R.H.; Li, X.H.; Wang, Z.X.; Zhang, H. Electrochemical analysis graphite/electrolyte interface in lithium-ion batteries: p-Toluenesulfonyl isocyanate as electrolyte additive. Nano Energ. 2017, 34, 131-140. (30) Wongittharom, N.; Wang, C.H.; Wang, Y.C.; Fey, T.K.; Li, H.Y.; Wu, T.Y.; Lee, T.C.; Chang, J.K. Charge-storage performance of Li/LiFePO4 cells with additive-incorporated ionic liquid electrolytes at various temperatures. J. Power Sources 2014, 260, 268-275. (31) Li, B.; Wang, Y.; Rong, H.; Wang, Y.; Liu, J.; Xing, L.; Xu, M.; Li, W. A novel electrolyte with the ability to form a solid electrolyte interface on the anode and cathode of a LiMn2O4/graphite battery. J. Mater. Chem. A 2013, 1, 12954-12961. (32) Xu, M.; Zhou, L.; Dong, Y.; Chen, Y.; Demeaux, J.; Macintosh, A.D.; Garsuch, A.; Lucht, B.L. Development of novel lithium borate additives for designed surface modification of high voltage LiNi0.5Mn1.5O4 cathodes. Energ. Environ. Sci. 2016, 9, 308-1319. (33) Chang, C.C.; Lee, K.Y.; Lee, H.Y.; Su, Y.H.; Her, L.J. Trimethyl borate and triphenyl borate as electrolyte additives for LiFePO4 cathode with enhanced high temperature performance. J. Power Sources 2012, 217, 524-529. (34) Chang, C.C.; Pan, P.I.; Wu, C.M.; Kao, H.J. Mixture of ionic liquid and organic carbonate as an electrolyte for LiFePO4 battery. Int. J. Electrochem. Sci. 2016, 11, 5327-5341. (35) Li, Q.; Jiao, S.; Luo, L.; Ding, M.S.; Zheng, J.; Cartmell, S. S.; Wang, C.M.; Xu, K.; Zhang, 30


Page 30 of 33

Page 31 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


J.G.; Xu, W. Wide-temperature electrolytes for lithium-ion batteries. ACS Appl. Mater. Interfaces 2017, 9, 18826. (36) Zhu, Y.; Rong, H.; Mai, S.; Luo, X.; Li, X.; Li, W. Significantly improved cycle ability of lithium manganese oxide under elevated temperature by an easily oxidized electrolyte additive. J. Power Sources 2015, 299, 485-491. (37) Cai, Z.; Liu, Y.; Zhao, J.; Li, L.; Zhang, Y.; Zhang, J. Tris(trimethylsilyl) borate as electrolyte additive to improve performance of lithium-ion batteries. J. Power Sources 2012, 202, 341-346. (38) Padhi, A. K.; Goodenough, J. B.; Nanjundaswamy, K. S. Phospho-olivines as positive-electrode materials for rechargeable lithium batteries. J. Electrochem. Soc. 1997, 144, 1188-1194. (39) Levi, M. D.; Salitra, G.; Markovsky, B.; Teller, H.; Aurbach, D.; Heider, U.; Heider, L. Solid-state electrochemical kinetics of Li-ion intercalation into Li1- xCoO2: simultaneous application of electroanalytical techniques SSCV, PITT, and EIS. Cheminform. 1999, 30, 1279-1289. (40) Lu, Y.; Xu, S.; Shu, J.; Aladat, W.I.A.; Archer, L.A. High voltage LIB cathodes enabled by salt-reinforced liquid electrolytes. Electrochem. Commun. 2015, 51, 23-26. (41) Lee, H.; Han, T.Y.; Cho, K.Y.; Ryou, M.H.; Lee, Y.M. Dopamine as a novel electrolyte additive for high-voltage lithium-ion batteries. ACS Appl. Mater. Interfaces 2016, 33, 21366. (42) Liu, J.W.; Song, X.; Zhou, L.; Wang, S.Q.; Feng, C.Q.; Guo, Z.P. Fluorinated Phosphazene Derivative - a Promising Electrolyte Additive for High Voltage Lithium Ion Batteries: From Electrochemical Performance to Corrosion Mechanism. Nano Energ. 2018, 46, 404-414. (43) Lu, Y.Y.; Tu, Z.Y.; Jonathan, S.; Lynden, A.A. Stable lithium electro-deposition in salt-reinforced electrolytes. J. Power Sources 2015, 279, 413-418. (44) Rong, H.; Xu, M.; Xie, B.; Lin, H.; Zhu, Y.; Zheng, X.; Huang, W.; Liao, Y.; Xing, L.; Li, W. A novel imidazole-based electrolyte additive for improved electrochemical performance at elevated temperature of high-voltage LiNi0.5Mn1.5O4 cathodes. J. Power Sources 2016, 329, 586-593. (45) Li, J.; Xing, L.; Zhang, R.; Chen, M.; Wang, Z.; Xu, M.; Li, W. Tris (trimethylsilyl) borate as an electrolyte additive for improving interfacial stability of high voltage layered lithium-rich oxide cathode/carbonate-based electrolyte. J. Power Sources 2015, 285, 360-366. 31



(46) Xu, M.Q.; Zhou, L.; Hao, L.S.; Xing, L.D.; Li, W.S.; Lucht, B.L. Investigation and application of lithium difluoro(oxalate)borate (LiDFOB) as additive to improve the thermal stability of electrolyte for lithium-ion batteries. J. Power Sources 2015, 196, 6794-6801. (47) Morigaki, K.I.; Otha, A. Analysis of the surface of lithium in organic electrolyte by atomic force microscopy, Fourier transform infrared spectroscopy and scanning auger electron microscopy. J. Power Sources 1998, 76, 159-166. (48) Zhu, Y.M.; Luo, X.Y.; Zhi, H.Z.; Liao, Y.H.; Xing, L.D.; Xu, K.; Li, W.S. Diethyl (thiophen-2-ylmethyl) phosphonate: a novel multifunctional electrolyte additive for high voltage batteries. J. Mater. Chem. A 2018, 6, 10990

32


Page 32 of 33

Page 33 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


505x390mm (300 x 300 DPI)


N,N-Dimethylformamide Electrolyte Additive Via a ... - ACS Publications

Recommend Documents