Stabilizing a High-Voltage Lithium-Rich Layered Oxide Cathode with a

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Stabilizing High Voltage Lithium-Rich Layered Oxide Cathode with a Novel Electrolyte Additive JIanlian Lan, Qinfeng Zheng, Hebing Zhou, Jianhui Li, Lidan Xing, Kang Xu, Weizhen Fan, Le Yu, and Weishan Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b07441 • Publication Date (Web): 17 Jul 2019 Downloaded from pubs.acs.org on July 19, 2019

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ACS Applied Materials & Interfaces

Stabilizing High Voltage Lithium-Rich Layered Oxide Cathode with a Novel Electrolyte Additive

Jianlian Lana, Qinfeng Zhenga, Hebing Zhouab, Jianhui Lia, Lidan Xingab, Kang Xu*c, Weizhen Fand, Le Yud, Weishan Li*ab

a

School of Chemistry and Environment, South China Normal University, Guangzhou 510006, China b

National and Local Joint Engineering Research Center of MPTES in High Energy and Safety LIBs, Engineering Research Center of MTEES (Ministry of Education), and Key Lab. of ETESPG(GHEI), South China Normal University, Guangzhou 510006, China c

Electrochemistry Branch, Sensor and Electron Devices Directorate, Power and Energy Division, U.S. Army Research Laboratory, Adelphi, MD 20783, USA. d

Guangzhou Tinci Material Technology Co., Ltd, Guangzhou 510760, China

ABSTRACT： We report a novel electrolyte additive, bis(trimethylsilyl)carbodiimide, that effectively stabilizes high voltage lithium-rich oxide cathode. Charge/discharge tests demonstrate that even trace amount of bis(trimethylsilyl)carbodiimide in a baseline electrolyte improves the cycling stability of this cathode significantly, either in Li-based half cells or graphite-based full cells, where the capacity retention after 200 cycles between 2 V and 4.8 V at 0.5 C is enhanced from 40% to 72% and 49% to 77%, respectively. Analyses using physical characterizations and theoretical calculations reveal that this additive not only builds a protective film on cathode, but also eliminates the detrimental hydrogen fluoride via its strong coordination with hydrogen fluoride or proton. KEYWORD: Lithium-rich layered oxide; Bis(trimethylsilyl)carbodiimide; Electrolyte additive; Protective film; Hydrogen fluoride. 1.

INTRODUCTION 1

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Lithium-ion batteries (LIBs) have become the most reliable rechargeable power sources since their commercialization in 1990’s, on account of their energy density and long cycle life compared with other rechargeable batteries.1-5 Thanks to their diversified electrode chemistries, LIBs are entering new fields

such

as

electric

vehicles

and

renewable

energy

storage.6-10

Lithium-rich

oxide,

xLi2MnO3·(1-x)LiMO2 (M = Ni, Co, Mn, LLO), is one of such chemistries that meets the stringent requirements of energy densities, with a promised specific capacity of over 250 mAh g-1,11-13 far higher than the conventional cathodes such as LiCoO2 (around 145 mAh g-1),14, 15 LiFePO4 (around 165 mAh g−1),16, 17 spinel LiMn2O4 (around 120 mAh g-1),18-21 and LiNi0.8Co0.15Al0.05O2 (around 180 mAh g-1).22, 23

However, LLO exhibits poor cycling stability, mainly originated from its unstable interface with

LiPF6-based carbonate electrolyte,9,

24-28

which are known for detrimental species such as hydrogen

fluoride (HF).29-32 To reinforce the LLO/electrolyte interface, various strategies have been adopted, including doping and coating.33-37 Comparatively, adding some electrolyte components is the most convenient and cost-efficient. It has been reported that some silicon-containing electrolyte additives, such as tris(trimethylsilyl)borate

(TMSB),39,

40

tris(trimethylsilyl)phosphite

(TMSP),33

or

lithium

trimethylsilyl)methanesulfonate (TMSOMs),41 can effectively improve the cycling stability of LLO by forming a protective film on LLO, which is generated by the preferential oxidation of the additive over the main components, salt and solvents. Additionally, these silicon-containing electrolyte additives are able to withstand high voltage.42, 43 Besides the gas generation, it has been known that hydrogen fluoride (HF), formed from thermal and electrochemical decomposition of the electrolyte salt, is especially detrimental to the cycling stability of transition metal oxide based cathodes. 32, 44, 45 It can potentially activate a series of harmful 2


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decompositions. The most detrimental among these parasitic reactions is the dissolution of transition metal ions from cathode lattice, which eventually deposit on anode, and consequently accelerate the sustained electrolyte decomposition and continuous interface resistance build-up. Therefore, HF-mitigation is of vital importance to LLO application. In this work, a novel electrolyte additive, bis(trimethylsilyl)carbodiimide (BTMSC) is reported to improve the cycling stability of LLO. Electrochemical measurements, theoretical calculations and physical characterizations certified that BTMSC has higher oxidative activity than other electrolyte solvents and can oxidize prior to those solvents creating a silicon-based as well as nitrogen-based cathode electrolyte interface (CEI) on LLO surface, which significantly improve the interface stability of LLO/electrolyte. What’s more, BTMSC containing nitrogen that has strong electron-drawing ability is capable of capturing proton or HF thus mitigating the activity of these fluoride species in the electrolyte solution. Charge/discharge tests show that the cyclic stability of LLO/Li half cells and LLO/graphite full cells has a dramatic improvement after applying 1 wt. % BTMSC-containing electrolyte. 2. EXPERIMENTAL SECTION 2.1 Electrode Preparation and Cell Assembly A typical LLO, Li1.2Mn0.55Ni0.15Co0.1O2, was selected in this work and prepared through coprecipitation method as described in previous reports.32, 46, 47 The LLO electrode slurry is composed of Li1.2Mn0.55Ni0.15Co0.1O2, poly(vinylidenedifluoride) (PVdF), and acetylene carbon black (AB) (8:1:1 in weight), while the ingredient of graphite electrode consists of artificial graphite, super-P and KS6 (conductive agents), and PVdF (89:2:4:5 in weight). The two electrodes were coated on the Al foil and Cu foil, respectively and dried under 120℃ for around 12 hours under vacuum condition. The loading 3



mass of the active material for LLO/graphite full cells was estimated according to the N/P value of 1.4, which N and P stand for the specific capacity of graphite anode (350 mAh g−1) and LLO cathode (200 mAh g−1), respectively. The BTMSC additive (98%) was purchased from Acros Industrial Inc, China. The standard electrolyte (baseline electrolyte) that dissolves 1.0 M LiPF6 in the solvents (diethyl carbonate (DEC) + ethylene carbonate (EC) + ethyl methyl carbonate (EMC) (2:3:5, in weight)) was obtained from Guangzhou Tinci Materials Technology Co. Ltd, China. The electrolyte additive was added into the baseline at varying concentrations (0.5%, 1%, 2% in weight). All electrolyte preparation process was conducted in a glovebox (MBraun, Germany) filled with high-purity Ar, where the contents of water vapor and oxygen were kept below 0.1 ppm. LLO/Li, LLO/graphite and graphite/Li 2025-coin cells with a Celgard 2400 separator were assembled in the glovebox. 2.2 Electrochemical and Physical Characterizations All charge/discharge tests were completed on a Land cell test system (Wuhan, China). The LLO/Li half cells and LLO/graphite full cells were conducted galvanostatically at 0.1 C (1 C = 200mAh g-1) for initial three cycles and subsequent cycles at 0.5 C respectively between 2 V and 4.8 V, whereas the graphite/Li was discharged to 0.005 V, and then charged to 2.5 V at the same current rate of 0.2 C. The linear sweep voltammetry (LSV) was conducted in a transparent V-type cells on a Solartro-1480 instrument (England), whose potential was swept from open-circuit voltage to 6 V(vs. Li/Li+) at a rate of 0.1 mV s-1. The chronoamperometry was conducted on LLO/Li half cells that were firstly activated for two cycles at 0.1 C, charged to 4.8 V at 0.5 C, and then held at a constant voltage of 4.8 V for 20 hours to record the corresponding current decay. The self-discharge of the LLO/Li half cells and LLO/graphite full cells were monitored, which were kept static for 30 days at room temperature and for 200 hours at 50℃, respectively, after cycling at 0.1 C for initial three cycles firstly 4


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and then charged at 0.5 C to 4.8 V to record the voltage decay with the time on the LAND cell test system. Electrochemical impedance measurement was performed at discharged state using a PGSTAT-30 electrochemical station (Autolab, Metrohm, Netherlands). The frequency range used is 105 -10-2 Hz, with a potential amplitude of 5 mV. All cycled electrodes used for physical characterizations were washed with DMC for three times to get rid of the residual electrolyte and LiPF6 salt, and then dried at lease 12h under vacuum at room temperature. X-ray diffraction (XRD, Bruker D8 ADVANCE, Germany) was used to testify the structural stability of LLO. Inductively coupled plasma–mass spectrometry using atomic emission spectrometer (ICP-AES) was used to monitor the dissolution of transitional metal from electrodes. The lithium electrodes recovered from the cycled cells were dissolved into the 4% HNO3 and then diluted to 50 mL. To evaluate the capability of BTMSC to sacrifice HF, electrolytes under different processing conditions (adding water or HF and storing under room temperature or 55℃) were analyzed with 19F NMR on spectrometer (Vavian 400, USA). The morphology observation was executed though scanning electron microscopy (SEM, JEM-6510, Japan) and transmission electron microscopy (TEM, JEM-2100HR, Japan). X-ray photoelectron spectrum (XPS, Thermo Fisher Scientific, UK, with a monochromatic Al Kα X-ray source (excitation energy = 1468.6 eV)) was used to analyze the surface chemistry. 2.3 Calculations Gaussian 09 package was employed to execute theoretical calculations. The geometric structures were all optimized with the B3LYP/6-311++G (d) and B3LYP/6-311++G (d, p) levels. The polarized continuum model (PCM) with a dielectric constant of 20.5 (acetone, which is close to that of carbonate-based electrolyte) was used to optimize the equilibrium state structures.48-50 Adiabatic 5



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ionization energy (AIE) was attained from the free energy (G), for an instance, AIE(EMC/EMC+) = [G(EMC+)-G(EMC)]. And the oxidation potential (Eox) and binding energy (Eb) were calculated as the following formula: 51 Eox(Li/Li+) = [G(M+)-G(M)]/F-1.4 V

1

Eb(EC-Li+) = [E(EC-Li+)-E(EC)-E(Li+)]

2

Where the G(M) and G(M+) stand for the free energy of the species M and its oxidized form M+ at 298.15K, respectively, and F is the Faraday constant. 3.

RESULTS AND DISCUSSION

3.1 Oxidation Activity of BTMSC-Containing Electrolyte An oxidation potential lower than the rest of the electrolyte components is a pre-requisite for a film forming electrolyte additive, which ensures the additive instead of the other electrolyte components dominates the film chemistry. 22 To assess the change of oxidation stability in electrolytes caused by BTMSC, LSV was conducted, which shows no characteristic peak associated to the presence of additive as compared with the base electrolyte. This absence of additive decomposition is not strange and has been observed previously with many effective additives, the most conspicuous example of which is vinylcarbonate (VC), because its decomposition kinetics is fast, and only trace amount of it is required to form a protective film. However, an obvious difference between the baseline and the additive-containing electrolyte starts to become conspicuous after 5 V (Figure 1(a)), with a much higher background current arising from the baseline electrolyte. Density functional theory (DFT) calculation shown (Figure 1(b)) predicts that the lowest oxidation potential of BTMSC makes it the preferential species to be oxidized, thus contributing to the major chemical sources for the protective film. The distance of Si-N bond increases from 1.75 Å to 1.81 Å after oxidation (Figure 1(c)), probably 6


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leading to the products with Si(CH3)3 and N=C=N radical terminal that potentially polymerizes with other radicals. In our previous work,44 we have found that the molecule’s oxidation activity is largely affected by the interaction between electrolyte solvents with PF6-. Figure 2 compares the AIE of various combinations of solvent- PF6-, solvent-solvents (Figure 2(b)) and solvent-PF6--solvent, which reveals that the combination of BTMSC and PF6- displays the lowest AIE, suggesting that this complex should oxidize before other solvents do. Meanwhile, PF6-, solvents and additive could also adsorb on the cathode surface, complicating the decomposition mechanism of additive or electrolyte, which confirms the diversified chemical species in cathode materials.52 An interaction exists between

solvents and Li+ during charge process, which enriches the complex with low combination energy at anode surface, while those having high combination energy will be enriched at cathode surface, leading to their preferential oxidation. Therefore the weak interaction between Li+ and additive is pivotal for the deposition of additives on the LLO cathode surface. Binding affinity is used to quantify the adsorption capacity that is related to the ability of oxidation.53 Figure 2(d) displays the optimized structures of the Li+-solvent combinations (EC, EMC, DEC, BTMSC). The Eb of BTMSC-Li+ (-11.34 KJ mol-1) is the highest as compared with EC-Li+ (-19.33 KJ mol-1), EMC-Li+ (-19.68 KJ mol-1), and DEC-Li+ (-20.5 KJ mol-1), which benefits the Li+-desolvation54 and assists in interphase formation. Summarizing the above experimental and computation results, we conclude that BTMSC can be easily oxidized. 3.2 Electrochemical Performances

Galvanostatic charge/discharge tests were conducted to demonstrate the effect of BTMSC on electrochemical performances of LLO/Li half cells (Figure 3(a)). There are many aspects that affect the cycling performances of LLO, including the increased interfacial impedance due to the accumulated 7



products from electrolyte decomposition, the decreased discharge voltage plateau due to phase transformation from layered to spinel, and the structural destruction due to the attack from HF.32 Thanks to the high charge voltage (4.8 V), all the cells deliver an initial capacity of as large as 250 mAh g-1 at 0.1 C, which is highly dependent of the composition of LLO.55-59 In the baseline electrolyte, the LLO behaves stable before 100 cycles, although minor capacity loss is observed. This initial capacity loss can be ascribed to the slow phase transformation that is inevitable for the samples enforced by doping56, coating59, or using electrolyte additive.57, 58 After the 130th cycle, however, the LLO cycled in baseline electrolyte suffers a sudden capacity fading, which can be ascribed to the

structural destruction.40, 60 In the BTMSC-containing electrolyte, the LLO behaves similarly to that in the baseline electrolyte, but stable up to 200 cycles, highlighting the contribution of BTMSC. The superior cycling stability of BTSMC-containing cells should originate from a stable interface between electrode and electrolyte formed by BTMSC, which not only preferentially oxidizes but also removes harmful HF. This conclusion would be further confirmed in the following research. Among all additive concentrations used, 1wt. % BTMSC seems optimum, which was selected for the following studies. Figure 3(b) shows the initial charge/discharge profile of LLO/Li half cells cycled in baseline and 1wt. % BTMSC-containing electrolyte, where the peak near 4.0 V stands for the delithiation process accompanied with the oxidization of Ni and Co (from Ni2+ , Ni3+ to Ni3+ , Ni4+ and Co3+ to Co4+), and Li2MnO3 activation occurs at around 4.5V. It is clearly visible that the coulombic efficiency (CE) for 1st cycle of the LLO/Li cells in presence of BTMSC is slightly lower, which may be associated with the BTMSC oxidation prior to other solvents. However, the CE for LLO/Li half cells with BTMSC is always higher than baseline electrolyte except the first cycle shown in Figure 3(a), indicating that BTMSC has the ability to stabilize the interface of LLO/electrolyte. The improvement in interfacial 8


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stability between LLO and electrolyte should also be visualized in the chronoamperometry (Figure 3(c)). Higher residual current for the LLO electrode in the baseline electrolyte reflects severe electrolyte oxidative decomposition during constant voltage holding process at 4.8 V, confirming the oxidative stability of BTMSC-containing electrolyte is improved. The improved interfacial stability of LLO with additive, BTMSC, can also be proved by impedance spectra (Figure S1), which consist of two overlapped semicircles and a sloped line. For LLO/Li half cells. The two overlapped semicircles represent the interfacial resistance from cathode film (Rfilm) and the charge-transfer process (Rct), while a sloped line stands for the diffusion of lithium ion (Wf) in the LLO electrode.60 The sum of interfacial resistances (Rfilm + Rct) increases with cycling in the baseline electrolyte, while BTMSC stabilizes it with cycling (Figure S1(c)), as a result of suppressing sustained decomposition of electrolyte components. Self-discharge behaviors of the half cells using electrolytes with and without additive were also investigated (Figure 3(d)). The voltage slowly decays at the beginning in baseline electrolyte. However, after about 18 days, this voltage rapidly drops to around 1.2 V. Again, BTMSC stabilizes such voltage decay, obviously supporting the argument that a BTMSC-based film protects the carbonate electrolyte from decomposing. 3.3. Effect of BTMSC on LLO Structure To reveal the structural damage of the cycled electrodes, X-ray diffraction (XRD) was performed on the recovered electrode after 200 cycles (Figure 4a), showing that the intensity of all peaks becomes significantly lower if cycled in the baseline electrolyte, indicating that LLO structure is seriously compromised in the baseline electrolyte after 200 cycles, while the cycled electrodes with BTMSC mitigate such delirious effect. The content of dissolved metal ions from LLO on anode surface, which may be mainly caused by HF generated from electrolyte, was also analyzed using ICP-AES (Figure 9



4(b)). The deposition content of nickel, cobalt, manganese as detected on Li plate is obviously lower from electrolyte with additive. Hence, a cathode film from BTMSC provides strong protection for both cathode and electrolyte. In addition, discharge profiles at varying cycles and the corresponding differential capacity for LLO electrodes reveal significant difference induced by electrolytes (Figure S2). Three main reduction process are detected: the peak around 4.5V (Re 1) stands for Li occupation in octahedral sites, Re2 at 3.7 V for Li occupation in octahedral sites associated with the Ni4+/Ni2+ and Co4+/Co3+, and the peak at < 3.5 V (Re 3) is Li occupation in octahedral sites related to Mn4+ /Mn3+.61 In this particular case, comparing Figure S2(c) with Figure S2(d) reveals that all the reduction peaks move to the left. However the extent of shift depends on electrolyte, with the baseline most serious, whose Re1 and Re3 peaks almost disappear. Meanwhile, the presence of additive maintains these peaks at distinct intensities, confirming that BTMSC indeed protects LLO from destroying. 3.4. Morphology and Composition on the Surface of LLO Electrode with and without Additive SEM and TEM images were collected from the cycled electrodes. Comparing Figure 5(a) with (b) and (c), the electrode cycled in the presence of additive is obviously similar with the fresh electrode, while the electrode recovered from the baseline electrolyte is covered with significant amount of electrolyte decomposition products during the 200 cycles. It can be found by comparing the fresh electrode (figure 5(d)), a thin (~ 6nm) and uniform polymeric film is detected on the LLO electrode recovered from BTMSC-based electrolyte (Figure 5(f)), while the interface of LLO electrode recovered from baseline electrolyte seems irregular in thickness ( Figure 5(e)). Both SEM and TEM suggest the protective film generated by additive greatly can control the continuous electrolyte decomposition. Chemical analysis via XPS identified variety of decomposition products from electrolyte components as well as from additive. C-C at 284.6eV correlates with conductive carbon black. C-H and C-F located 10


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at 285.5ev and 291eV, respectively, correspond to PVdF6, 62 and C-O (286.5eV). C=O (288.6eV) and Li2CO3 (289.9eV, 531eV shown in O1s spectra) should be assigned to the lithium alkyl carbonate and Li2CO3. The peaks at 533.1eV, 531.9eV and 529.5eV are ascribed to C-O, C=O and a metal oxide in LLO. 41, 63, 64 PVdF is located at 688eV. LiF is generated possibly due to the reaction of HF with Li ions (such as HF + Li2CO3 = LiF + H2O + CO2).31 Comparison of XPS reveals that much less electrolyte decomposition products were produced in presence of additive, as evidenced by the lower abundances of C1s, O1s, F1s, and P2p peaks (Figure 6). The reduction in peak intensity of LiF (684.5eV) by BTMSC suggests that it may get rid of HF. The additive also reduces the abundance of NiF2 at 685.2eV, which is produced by the reaction between Ni2+ and HF, and whose generation indicates the loss of active materials and the disintegration of cathode structure.65 Additionally, NiF2 as insulating material is also responsible for the increase of resistance.66 The similar mitigation effect of BTMSC was also observed on peak intensity of P-F species, which are visible in both P2p and F1s spectra as LixPOyFz and LixPFy.21,

37, 67

On the other hand, the appearance of N1s, and Si2p peaks directly

associates the additive decomposition to the mitigation of electrolyte decomposition. 3.5. HF Elimination by Additive. PF6- has been well established as source of fluorides when exposed to moisture (LiPF6 + H2O = 2HF + POF3 + LiF). It is also thermodynamically unstable, and decomposes into a strong Lewis acid PF5 that would trigger a series of reactions eventually producing HF or other P-F species, all of which will accelerate transitional metal dissolution.68 BTMSC containing N-Si bond can be considered as a novel HF scavenger, whose elimination of the initial HF can be demonstrated by quantitatively monitoring the change in HF-concentration in the electrolytes after being stored at high temperature for 60 h or with 1% (in volume) water for 12h to induce HF generation. 19F NMR spectra of both baseline 11



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and BTMSC-containing electrolytes undergoing the above protocols identify the one doublet peaks at lower than 80 ppm, attributed to PF6- rooted in LiPF6 (Figure 7). An offset occurs to these peaks at different experimental conditions, which should be ascribed to the various compositions of the electrolytes. The peaks at 83 and 84 ppm correspond to PO2F2- from thermal decomposition,28, 69 and singlet at 192 ppm to HF. Though these peaks can hardly be identified(Figure 7(a, c)), HF can be obviously seen as being eliminated upon the addition of BTMSC (Figure 7(b, d)). To further confirm the scavenging ability of BTMSC toward HF, 600ppm HF was deliberately added to the baseline as well as BTMSC-containing electrolyte, respectively, which were then stored for 12 hours. The peaks at 72 ppm and 73 ppm, attributed to PF6- and PO2F2- produced by hydrolysis of LiPF6, can be seen in both baseline and BTMSC-containing electrolytes31, 41, 70 (Figure S3). However, the peak at 192 ppm (HF) can only be seen in the baseline. This reduction of HF due to the scavenging capability of BTMSC directly leads to the reduction of transition metal dissolution (Figure 4(b)). As indicated by the blue circles in Figure 2(a), the oxidation of the solvent-PF6- complexes yields the destructive HF, which ultimately influences the cycling stability,44 while additive does not. The calculation using 6-311++G(d) basis set (Figure S4) shows the optimized structures and binding energy between X (X=BTMSC, DEC, EMC, EC) and Y (Y=HF, 2HF, H+, 2H+, F-), which conclude that the binding energy between BTMSC and HF and 2HF is lower than solvents. The binding energy between H+ dissociated from HF with BTMSC and solvents is compared (Figure S4(a ， b)), suggesting BTMSC preferentially combines with H+ over its interaction with F-. A noteworthy feature of this interaction is that there is a strong interaction between BTMSC and H+ or 2H+ to prevent the decomposition of solvents. Similar conclusion can be drawn when the calculation was performed by using (6-311++G(d, p)) basis set, as shown in Figure S5. According to the new peak shown in 12


19F

NMR spectra arising

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from the addition of water, HF or high temperature treatment, a reaction between additive and HF was speculated. In order to expound feasibility of the reaction, the energy (ΔG) for the reaction between BTMSC and HF was explored. From Figure S4(f), the estimated ΔG is -142 KJ mol−1, showing that the formation of a Si-F bond is easier energetically. LLO/Li half cells with HF-containing electrolytes were performed with cycling to establish the correlation between HF and electrochemical performances. When cycling in the 600ppm HF-containing electrolyte (Figure S6(a)), a sharp capacity drop occurs with baseline electrolyte, together with significant loss of materials from the electrode (inset of Figure S6 (a)), confirming that LLO structure suffers severe damage in the presence of HF. Besides, low and fluctuating coulombic efficiencies also ensue. In sharp contrast, when cycling in BTMSC-containing electrolyte, both capacity and coulombic efficiency of the half cells maintain stability, further backing up the argument that BTMSC indeed removes HF. 3.6. Cycling Stability of Graphite/Li and LLO/Graphite Cells Effect of BTMSC on the cycling performance of graphite/Li half cells and LLO/graphite full cells was also examined (Figure 8). Obviously, the first two charging/discharging curves of graphite/Li cells bear close resemblance (Figure 8(a, b)). The short reduction potential platform in the first discharging process is ascribed to the solid electrolyte interphase (SEI) generation of the EC-based electrolyte BTMSC displays a negligible effect on graphic/Li half cells, which can be confirmed by cycling performance shown in Figure 8(c). The (SEI) generation is responsible for the lower coulombic efficiency (Figure 8(d)).The effect of BTMSC can be verified again in the cycling stability of LLO/graphite full cells (Figure 8(e, f)), which improves the capacity retention from 49% to 77%, clearly benefitted from film formed by BTMSC and the elimination of HF. Besides ， the high temperature storage performance of LLO/graphite full cells with and without BTMSC was evaluated at 13



50 ℃ for 200 hours (Figure S7). The voltage of LLO/graphite full cells declines sharply in baseline electrolyte, while remains relative stable in BTMSC-containing electrolyte, indicating that BTMSC-derived film can effectively stabilize LLO. 4.

CONCLUSION Lithium-rich oxide suffers from an interfacial instability when it is cycled in LiPF6/carbonate

electrolytes. We address this issue by applying bis(trimethylsilyl)carbodiimide (BTMSC) as an electrolyte additive, which can be easily oxidized. Besides, nitrogen substructure belonging to BTMSC exhibits capability to scavenge H+ or HF. These capabilities enable BTMSC to form a protective film containing silicon and nitrogen-based on the cathode surface while mitigate the detrimental effect caused by HF species on transition metal dissolution from LLO. These features, as supported by experimental and calculated results, contribute to the significantly improved cycling stability of LLO in both Li-based half cell and graphite-based full cell.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Electrochemical impedance spectra of LLO/Li cells after 3, 200 cycles; Discharge curves and corresponding dQ/dV profiles of LLO/Li half cells;

19F

NMR spectra of baseline and

BTMSC-containing electrolytes with 600ppm; Optimized structures and binding energy (Eb, KJ mol-1) of X-HF, X-2HF-, X-H+, X-2H+, X-F- (X=BTMSC, EC, EMC, DEC) by 6-311++G(d) and 6-311++G(d, p), possible reaction between BTMSC and HF; Cycling stability and photos of lithium electrode after cycling for 150 cycles and corresponding coulombic efficiency of LLO/Li half cells in 14


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the 600 ppm HF-containing electrolyte; Self-discharge profiles of LLO/graphite full cells at 50℃. AUTHOR INFORMATION Corresponding Authors * E-mail: [email protected] * E-mail: [email protected] * E-mail: [email protected]

NOTES The authors declare no competing financial interest.

ACKNOWLEGEMENTS This work is financially supported by the National Natural Science Foundation of China (Grant No. 21872058) and the Key Project of Science and Technology in Guangdong Province (Grant No. 2017A010106006).

15



REFERENCES (1) Armand, M.; Tarascon, J.-M. Building Better Batteries. Nature 2008, 451, 652-657. (2) Andre, D.; Kim, S.-J.; Lamp, P.; Lux, S. F.; Maglia, F.; Paschos, O.; Stiaszny, B. Future Generations of Cathode Materials: An automotive Industry Perspective. J. Mater. Chem A 2015, 3, 6709-6732. (3) Choi, J. W.; Aurbach, D. Promise and Reality of Post-Lithium-Ion Batteries with High Energy Densities. Nat. Rev. Mater. 2016, 1, 16013. (4) Dunn, B.; Kamath, H.; Tarascon, J.-M. Electrical Energy Storage for the Grid: A Battery of Choices. Science 2011, 334, 928-935. (5) Nitta, N.; Wu, F.; Lee, J. T.; Yushin, G. Li-Ion Battery Materials: Present and Future. Mater. Today 2015, 18, 252-264. (6) Wang, L.; Ma, Y. L.; Li, Q.; Zhou, Z. X.; Cheng, X. Q.; Zuo, P. J.; Du, C. Y.; Gao, Y. Z.; Yin, G. P. 1,3,6-Hexanetricarbonitrile as Electrolyte Additive for Enhancing Electrochemical Performance of High Voltage Li-Rich Layered Oxide Cathode. J. Power Sources 2017, 361, 227-236. (7) Marom, R.; Amalraj, S. F.; Leifer, N.; Jacob, D.; Aurbach, D. A Review of Advanced and Practical Lithium Battery Materials. J. Mater. Chem. A 2011, 21, 9938-9954. (8) Wei, Y.; Zheng, J. X.; Cui, S. H. ; Song, X. H.; Su, Y. T.; Deng, W. J.; Wu, Z. Z.; Wang, X. W.; Wang, W. D.; Rao, M. M.; Lin, Y.; Wang, C. M.; Amine, K.; Pan, F. Kinetics Tuning of Li-Ion Diffusion in Layered Li(NixMnyCoz )O2. J. Am. Chem. Soc. 2015, 137, 8364-8367. (9) Yu, X. Q.; Lyu, Y. C.; Gu, L.; Wu, H. M.; Bak, S.-M.; Zhou, Y. N.; Amine, K.; Ehrlich, S N.; Li, H.; Nam, K.-W.; Yang, X.-Q. Understanding the Rate Capability of High-Energy-Density Li-Rich Layered Li1.2Ni 0.15Co0.1Mn0.55O2 Cathode Materials. Adv. Energy Mater. 2014, 4, 1300950. 16


Page 16 of 35

Page 17 of 35 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


(10) Li, D.; Wang, H. Q.; Zhou, T. F.; Zhang, W. C.; Liu, H. K.; Guo, Z. P. Unique Structural Design and Strategies for Germanium-Based Anode Materials toward Enhanced Lithium Storage. Adv. Energy Mater. 2017, 7, 1700488. (11) Martha, S. K.; Nanda, J.; Veith, G. M.; Dudney, N. J. Surface Studies of High Voltage Lithium Rich Composition: Li1.2Mn0.525Ni0.175Co0.1O2. J. Power Sources 2012, 216, 179-186. (12) Zheng, X. W.; Wang, X. S.; Cai, X.; Xing, L. D.; Xu, M. Q.; Liao, Y. H.; Li X. P.; Li, W. S. Constructing a Protective Interface Film on Layered Lithium-Rich Cathode Using an Electrolyte Additive with Special Molecule Structure. ACS Appl. Mater. Interfaces 2016, 8, 30116-30125. (13) Xiang, X. D.; Knight, J. C.; Li, W. S.; Manthiram, A. Understanding the Effect of Co3+ Substitution on the Electrochemical Properties of Lithium-Rich Layered Oxide Cathodes for Lithium-Ion Batteries. J. Phys. Chem. C 2014, 118, 21826-21833. (14) Etacheri, V.; Marom, R.; Elazari, R.; Salitra G.; Aurbach, D. Challenges in the Development of Advanced Li-Ion Batteries: A Review. Energy Environ. Sci. 2011, 4, 3243-3262. (15) Zhu, Y. M.; Luo, X. Y.; Zhi, H. Z.; Yang, X. R.; Xing, L. D; Liao, Y. H.; Xu, M. Q.; Li, W. S. Structural Exfoliation of Layered Cathode under High Voltage and Its Suppression by Interface Film Derived from Electrolyte Additive. ACS Appl. Mater. Interfaces 2017, 9, 12021-12034. (16) Li, B. Z.; Wang, Y.; Xue, L.; Li, X. P.; Li, W. S. Acetylene Black-Embedded LiMn0.8Fe0.2PO4C Composite as Cathode for Lithium Ion Battery. J. Power Sources 2013, 232, 12-16. (17) Cai, Z. P.; Liang, Y.; Li, W. S.; Xing, L. D.; Liao, Y. H. Preparation and Performances of LiFePO4 Cathode in Aqueous Solvent with Polyacrylic Acid as A Binder. J. Power Sources 2009, 189,547-551. (18) Zhu, Y. M.; Rong, H. B.; Mai, S. W.; Luo, X. Y.; Li, X. P.; Li, W. S. Significantly Improved Cyclability of Lithium Manganese Oxide under Elevated Temperature by an Easily Oxidized 17



Electrolyte Additive. J. Power Sources 2015, 299, 485-491. (19) Lin, H. B.; Huang, W. Z.; Rong, H. B.; Hu, J. N.; Mai, S. W.; Xing, L. D.; Xu, M. Q.; Li, X. P.; Li, W. S. Surface Natures of Conductive Carbon Materials and Their Contributions to Charge/Discharge Performance of Cathodes for Lithium Ion Batteries. J. Power Sources 2015, 287, 276–282. (20) Lin, H. B.; Hu, J. N.; Rong, H. B.; Zhang, Y. M.; Mai, S. W.; Xing, L. D.; Xu, M. Q.; Li, X. P.; Li, W. S. Porous LiMn2O4 Cubes Architectured with Single-Crystalline Nanoparticles and Exhibiting Excellent Cyclic Stability and Rate Capability as Cathode of Lithium Ion Battery. J. Mater. Chem. A 2014, 2, 9272-9279. (21) Chen, M.; Chen, D. R.; Liao, Y. H.; Zhong, X. X.; Li, W. S.; Zhang, Y. G. Layered Lithium-Rich Oxide Nanoparticles Doped with Spinel Phase: Acidic Sucrose-Assistant Synthesis and Excellent Performance as Cathode of Lithium Ion Battery. ACS Appl. Mater. Interfaces 2016, 8, 4575-4584. (22) Zheng, Q. F.; Xing, L. D.; Yang, X. R.; Li, X. F.; Ye, C. C; Wang, K.; Huang, Q. M.; Li, W. S. N-Allyl-N,N-Bis(trimethylsilyl)amine as a Novel Electrolyte Additive to Enhance the Interfacial Stability of a Ni-Rich Electrode for Lithium-Ion Batteries. ACS Appl. Mater. Interfaces 2018, 10, 16843-16851. (23) Liu, L. L.; Du C. J.; Wang, S. l.; Chen, S. M. Three New Bifunctional Additives for Safer Nickel-Cobalt-Aluminum Based Lithium Ion Batteries. Chinese Chem. Lett. 2018, 29, 1781-1784. (24) Ito, A.; Li, Sato, D. C.; Y. C.; Arao, M.; Watanabe, M.; Hatano, M.; Horie, H.; Ohsawa, Y. Cyclic Deterioration and Its Improvement for Li-Rich Layered Cathode Material Li[Ni0.17Li0.2Co0.07Mn 0.56]O2.

J. Power Sources 2010, 195, 567-573.

(25) Tu, W. Q.; Xing, L. D.; Xia, P.; Xu, M. Q; Liao, Y. H.; Li, W. S. Dimethylacetamide as a 18


Page 18 of 35

Page 19 of 35 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


Film-Forming Additive for Improving the Cyclic Stability of High Voltage Lithium-Rich Cathode at Room and Elevated Temperature. Electrochim. Acta 2016, 204, 192-198. (26) Zheng, J. M.; Gu, M.; Xiao, J.; Zuo, P. J.; Wang, C. M.; Zhang, J.-G. Corrosion/Fragmentation of Layered Composite Cathode and Related Capacity/Voltage Fading during Cycling Process. Nano Lett. 2013, 13, 3824-3830. (27) Xu, B.; Fell, C. R.; Chi, M. F.; Meng, Y. S. Identifying Surface Structural Changes in Layered Li-Excess Nickel Manganese Oxides in High Voltage Lithium Ion Batteries: A Joint Experimental and Theoretical Study. Energy Environ. Sci. 2011, 4, 2223-2233. (28) Choi, N.-S.; Han, J.-G.; Ha, S.-Y.; Park, I.; Back, C.-K. Recent Advances of the Electrolytes for Interfacial Stability of High-Voltage Cathodes in Lithium-Ion Batteries. RSC Adv. 2015, 5, 2732-2748. (29) Song, B. H.; Liu, Z. W.; Lai, M. O.; Lu L. Structural Evolution and the Capacity Fade Mechanism upon Long-Term Cycling in Li-Rich Cathode Material. Phys. Chem. Chem. Phys. 2012, 14, 12875-12883. (30) Wagner, R.; Korth, M.; Streipert, B.; Kasnatscheew, J.; Gallus, D. R.; Brox, S.; Amereller, M.; Cekic-Laskovic, I.; Winter, M. Impact of Selected LiPF6 Hydrolysis Products on the High Voltage Stability of Lithium-Ion Battery Cells. ACS Appl. Mater. Interfaces 2016, 8, 30871-30878. (31) Wotango, A. S.; Su, W.-N.; Leggesse, E. G.; Haregewoin, A. M.; Lin, M.-H.; Zegeye, T. A.; Chen J.-H.;

Hwang,

B.-J.

Improved

Interfacial

Properties

of

MCMB

Electrode

by

1-

(Trimethylsilyl)imidazole as New Electrolyte Additive to Suppress LiPF6 Decomposition. ACS Appl. Mater. Interfaces 2017, 9, 2410-2420. (32) Ye, C. C.; Tu, W. Q.; Yin, L. M.; Zheng, Q. F.; Wang, C.; Zhong, Y. T.; Zhang, Y. G.; Huang, Q. M.; Xu, K.; Li, W. S. Converting Detrimental HF in Electrolyte into a Highly-Fluorinated Interphase 19



on Cathode. J. Mater. Chem. A 2018, 6, 17642-17652. (33) Han, J. G.; Lee, S. J.; Lee, J.; Kim, J.-S.; Lee, K. T.; Choi, N.-S. Tunable and Robust Phosphite-Derived Surface Film to Protect Lithium-Rich Cathodes in Lithium-Ion Batteries, ACS Appl. Mater. Interfaces 2015, 7, 8319-8329. (34) Liu, H.; Du, C. Y.; Yin, G. P.; Song, B. P.; Zuo, J.; Cheng X. Q.; Ma, Y. L.; Gao, Y. Z. An Li-Rich Oxide Cathode Material with Mosaic Spinel Grain and a Surface Coating for High Performance Li-Ion Batteries. J. Mater. Chem. A 2014, 2, 15640-15646. (35) Xie, D. J.; Li, G. S.; Li, Q.; Fu, C. C.; Fan, J. M.; Li, L. P. Improved Cycling Stability of Cobalt-Free Li-Rich Oxides with a Stable Interface by Dual Doping. Electrochim. Acta 2016, 196, 505-516. (36) Yu, R. B.; Lin, Y. B.; Huang, Huang, Z. G. Investigation on the Enhanced Electrochemical Performances of Li1.2Ni0.13Co0.13Mn0.54O2 by Surface Modification with ZnO. Electrochim. Acta 2015, 173, 515-522. (37) Li, Q.; Li, G. S.; Fu, C. C.; Luo, D.; Fan, J. M.; Li, L. P. K+-Doped Li1.2Mn0.54Co0.13Ni0.13O2: A Novel Cathode Material with an Enhanced Cycling Stability for Lithium-Ion Batteries. ACS Appl. Mater. Interfaces 2014, 6, 10330-10341. (38) Zhang, X. F.; Belharouak, L.; Li, L.; Lei, Y.; Elam, J. W.; Nie, A.; Chen, X. Q.; Yassar, R. S.; Axelbaum, R. L. Structural and Electrochemical Study of Al2O3 and TiO2 Coated Li1.2Ni0.13Mn 0.54Co0.13O2

Cathode Material Using ALD. Adv. Energy Mater. 2013, 3, 1299-1307.

(39) Zhu, Y. M.; Luo, X. Y.; Xu, M. Q.; Zhang, L. P.; Yu, L.; Fan, W. Z.; Li, W. S. Failure Mechanism of Layered Lithium-Rich Oxide/Graphite Cell and Its Solution by Using Electrolyte Additive. J. Power Sources 2016, 317, 65-73. 20


Page 20 of 35

Page 21 of 35 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


(40) Li, J. H.; Xing, L. D.; Zhang, R. Q.; Chen, M.; Wang, Z. S.; Xu, M. Q.; Li, W. S. 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. (41) Lim, S. H.; Cho, W.; Kim, Y.-J.; Yim, T. Insight into the Electrochemical Behaviors of 5V-Class High-Voltage Batteries Composed of Lithium-Rich Layered Oxide with Multifunctional Additive. J. Power Sources 2016, 336, 465-474. (42) Yan, C.; Xu, Y.; Xia J. R.; Gong, C. R.; Chen, K. R. Tris(trimethylsilyl)borate as an Electrolyte Additive for High-Voltage Lithium-Ion Batteries Using LiNi1/3Mn1/3Co1/3O2 Cathode. J. Energ. Chem. 2016, 25, 659-666. (43) Wu, F.; Zhou, H.; Bai, Y.; Wang, H. L.; Wu, C. Toward 5 V Li-Ion Batteries: Quantum Chemical Calculation and Electrochemical Characterization of Sulfone-Based High-Voltage Electrolytes. ACS Appl. Mater. Interfaces 2015, 7, 15098−15107. (44) Yang, X. R.; Chen, J. W.; Zheng, Q. F.; Tu, W. Q.; Xing, L. D.; Liao, Y. H.; Xu, M. Q.; Huang, Q. M.; Cao, G. Z.; Li, W. S. Mechanism of Cycling Degradation and Strategy to Stabilize a Nickel-Rich Cathode. J. Mater. Chem. A 2018, 6, 16149-16163. (45) Teng, X.; Zhan, C.; Bai, Y.; Ma, L.; Liu, Q.; Wu, C.; Wu, F.; Yang, Y. S.; Lu, J.; Amine, K. In-Situ Analysis of Gas Generation in Lithium Ion Batteries with Different Carbonate-Based Electrolytes. ACS Appl. Mater. Interfaces 2015, 7, 22751-22755. (46) Yi, T.-F.; Tao, W.; Chen, B.; Zhu, Y.-R.; Yang, S.-Y.; Xie, Y. High-performance xLi2MnO3. (1-x)LiMn1/3Co1/3Ni1/3O2 (0.1≤x≤0.5) as Cathode Material for Lithium-Ion Battery. Electrochim. Acta 2016, 188, 686-695. 21



(47) Liu, X. Q.; Guo, Z. M. Synthesis of Spherical Li1.167Ni0.2Co0.1Mn0.533O2 as Cathode Material for Lithium-Ion Battery via Co-precipitation. Prog. Nat. Sci-Mater. 2012, 22, 126-129. (48) Xing, L. D.; Borodin, O. Oxidation Induced Decomposition of Ethylene Carbonate from DFT Calculations-Importance of Explicitly Treating Surrounding Solvent. Phys. Chem. Chem. Phys. 2012, 14, 12838–12843. (49) Lin, Y. L.; Xu, M. Q. Wu, S. P.; Tian, Y. Y.; Cao, Z. G.; Xing, L. D. Li, W. S. Insight into the Mechanism of Improved Interfacial Properties between Electrodes and Electrolyte in the Graphite/LiNi 0.6Mn0.2Co0.2O2

Cell via Incorporation of 4-Propyl-[1, 3, 2]dioxathiolane-2, 2-dioxide (PDTD). ACS

Appl. Mater. Interfaces 2018, 10, 16400-16409. (50) Wu, S. P.; Lin, Y. L.; Xing, L. D.; Sun, G. Z.; Zhou, H. B. Xu, K.; Fan, W. Z.; Yu, L.; Li, W. S. Stabilizing LiCoO2/Graphite at High Voltages with an Electrolyte Additive. ACS Appl. Mater. Interfaces 2019, 11, 17940-17951. (51) Huang, W. N.; Xing, L. D.; Zhang, R. Q.; Wang, X. S.; Li, W. S. A Novel Electrolyte Additive for Improving the Interfacial Stability of High Voltage Lithium Nickel Manganese Oxide Cathode. J. Power Sources 2015, 293, 71-77. (52) Vatamanu, J.; Borodin, O.; Smith, G. D. Molecular Dynamics Simulation Studies of the Structure of a Mixed Carbonate/LiPF6 Electrolyte near Graphite Surface as a Function of Electrode Potential. J. Phys. Chem. C 2012, 11, 1114-1121. (53) Chen, J. H.; Zhang, H.; Wang, M. L.; Liu, J. H.; Li, C. H.; Zhang, P. X. Improving the Electrochemical Performance of High Voltage Spinel Cathode at Elevated Temperature by a Novel Electrolyte Additive. J. Power Sources 2016, 303, 41-48. (54) Park, M. H.; Lee, Y. S.; Lee, H. C.; Han, Y.-K. Low Li+ Binding Affinity: An Important 22


Page 22 of 35

Page 23 of 35 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


Characteristic for Additives to Form Solid Electrolyte Interphases in Li-Ion Batteries. J. Power Sources 2011, 196, 5109-5114. (55) Zhou, Z. X.; Ma, Y. L.; Wang, L.; Zuo, P. J.; Cheng, X. Q.; Du, C. Y.; Yin, G. P.; Gao, Y. Z. Triphenyl Phosphite as an Electrolyte Additive to Improve the Cyclic Stability of Lithium-Rich Layered Oxide Cathode for Lithium-Ion Batteries. Electrochim. Acta 2016, 216, 44-50. (56) Wang, D.; Huang, Y.; Huo, Z. Q.; Chen, L. Synthesize and Electrochemical Characterization of Mg-Doped Li-Rich Layered Li[Li0.2Ni0.2Mn0.6]O2 Cathode Material. Electrochim. Acta 2013, 107, 461-466. (57) Li, J. H.; Xing, L. D.; Wang, Z. S.; Tu, W. Q.; Yang, X. R.; Lin, Y. L.; Liao,Y. Q.; Xu, M. Q.; Li, W. S. Insight into the Capacity Fading of Layered Lithium-Rich Oxides and Its Suppression via a Film-Forming Electrolyte Additive. RSC Adv. 2018, 8, 25794-25801. (58) Zhuang, Y.; Du, F. H.; Zhu, L. L.; Cao, H. S.; Dai, H.; Adkins, J.; Zhou, Q.; Zheng, J. W. Trimethylsilyl(trimethylsiloxy)acetate as a Novel Electrolyte Additive for Improvement of Electrochemical Performance of Lithium-Rich Li1.2Ni0.2Mn0.6O2 Cathode in Lithium-Ion Batteries. Electrochim. Acta 2018, 290, 220-227. (59) Dannehl, N.; Steinmüller, S. O.; Szabó, D. V.; Pein, M.; Sigel, F.; Esmezjan, L.; Hasenkox, U.; Schwarz, B.; Indris, S.; Ehrenberg, H. High-Resolution Surface Analysis on Aluminum Oxide-Coated Li1.2Mn0.55Ni0.15Co0.1O2 with Improved Capacity Retention. ACS Appl. Mater. Interfaces 2018, 10, 43131-43143. (60) Tu, W. Q.; Xia, P. Xia,; Zheng, X. W. Zheng,; Ye, C. C.; Xu, M. Q.; Li, W. S. Insight into the Interaction between Layered Lithium-Rich Oxide and Additive-Containing Electrolyte. J. Power Sources 2017, 341, 348-356. 23



(61) Li, J. H.; Xing, L. D.; Zhang, L. P.; Yu, L.; Fan, W. Z.; Xu, M. Q.; Li, W. S. Insight into Self-Discharge of Layered Lithium-Rich Oxide Cathode in Carbonate-Based Electrolytes with and without Additive. J. Power Sources 2016, 32, 17-25. (62) Wang, C. Y.; Yu, L.; Fan, W. Z.; Liu, J. W.; Ouyang, L. Z.; Yang, L. C.; Zhu, M. 3, 3′-(Ethylenedioxy)dipropiononitrile as an Electrolyte Additive for 4.5 V LiNi1/3Co1/3Mn1/3O2/Graphite Cells. ACS Appl. Mater. Interface 2017, 9, 9630-9639. (63) Su, C.-C.; He, M. N.; Peebles, C.; Zeng, L.; Tornheim, A.; Liao, C.; Zhang, L.; Wang, J. Y.; Zhang, Z. C. Functionality Selection Principle for High Voltage Lithium-Ion Battery Electrolyte Additives. ACS Appl. Mater. Interface 2017, 9, 30686-30695. (64) Wang, Z. S.; Xing, L. D.; Li, J. H.; Xu, M. Q.; Li, W. S. Triethylborate as an Electrolyte Additive for High Voltage Layered Lithium Nickel Cobalt Manganese Oxide Cathode of Lithium Ion Battery. J. Power Sources 2016, 307, 587-592. (65) Han, J.-G.; Lee, J. B.; Cha, A.; Lee, T. K.; Cho, W.; Chae, S.; Kang, S. J.; Kwak, S. K.; Cho, J.; Hong, S. Y.; Choi, N.-S. Unsymmetrical Fluorinated Malonatoborate as an Amphoteric Additive for High-Energy-Density Lithium-Ion Batteries. Energy Environ. Sci. 2018, 11, 1552-1562. (66) Shi, Y.-L.; Shen, M.-F.; Xu, S.-D.; Qiu, X.-Y.; Jiang, L.; Qiang, Y.-H.; Zhuang, Q.-C.; Sun, S.-G. Electrochemical Impedance Spectroscopic Study of the Electronic and Ionic Transport Properties of NiF2/C Composites. Int. J. Electrochem. Sci. 2011, 6, 3399-3415. (67) Birrozzi, A.; Laszczynski, N.; Hekmatfar, M.; Zamory, J. V.; Giffin, G. A.; Passerini, S. Beneficial Effect of Propane Sultone and Tris(trimethylsilyl)borate as Electrolyte Additives on the Cycling Stability of the Lithium Rich Nickel Manganese Cobalt (NMC) Oxide. J. Power Sources 2016, 325, 525-533. 24


Page 24 of 35

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(68) Xu, G. J.; Liu, Z. H.; Zhang, C. J.; Cui, G. L.; Chen, L. Q. Strategies for Improving the Cyclability and Thermo-Stability of LiMn2O4-Based Batteries at Elevated Temperatures. J. Mater. Chem. A 2015, 3, 4092-4123. (69) Plakhotnyk, A. V.; Ernst, L.; Schmutzler, R. Hydrolysis in the System LiPF6-Propylene Carbonate-Dimethyl Carbonate-H2O. J. Fluorine Chem. 2005, 126, 27-31. (70) Song, Y.-M.; Han, J.-G.; Park, S.; Lee, K. T.; Choi, N.-S. A Multifunctional Phosphite-Containing Electrolyte for 5V-Class LiNi0.5Mn1.5O4 Cathodes with Superior Electrochemical Performance. J. Mater. Chem. A 2014, 2, 9506-9513.

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Figure captions Figure 1. LSV profiles of Pt electrode in the baseline and BTMSC-containing electrolytes (a); optimized structures and the corresponding oxidation potential (V, vs. Li /Li+) of BTMSC, EC, DEC, EMC (b); calculated bond length and corresponding optimized structures of BTMSC (c). Figure 2. Optimized structures and adiabatic ionization energy (AIE, KJ mol-1) of X-PF6-(a), BTMSC-X (b) and BTMSC-PF6--X (c) before and after one electron oxidation; Optimized structures and the relative binding energies (Eb, KJ mol-1) of X-Li+ (d). X = EC, EMC, DEC, and BTMSC. Figure 3. Cycling stability and coulombic efficiency (a), the initial charge-discharge profiles (b), chronoamperometric profiles at 4.8 V (c), and self-discharge profiles after three charge-discharge cycles (d) for LLO/Li coin cells in the baseline and BTMSC-containing electrolytes.

Figure 4. XRD patterns of LLO before and after 200 cycling (a) and contents of Ni, Co and Mn deposited on the lithium electrode after 200 cycles (b). Figure 5. SEM and TEM images of Li1.2Mn0.55Ni0.15Co0.1O2 before (a ， d) and after 200 cycles in electrolyte without (b，e) and with 1 wt. % BTMSC (c，f). Figure 6. XPS spectra of C1s, O1s, F1s, P2p, N1s, and Si2p of LLO after 200 cycles in electrolytes with and without BTMSC. Figure 7. 19F NMR spectra of baseline (blank line) and BTMSC-containing electrolytes (red line ) after storing for 60 hours (a, b) at 55℃ and adding 1 vol. % H2O for 12 hours (c, d) at room temperature. Figure 8. The first and second charging/discharging curves in electrolytes without (a) and with (b) BTMSC, cycling stability (c) and coulombic efficiency (d) for graphite/Li cells in electrolytes with and without BTMSC; Cycling stability (e) and coulombic efficiency (f) of Li1.2Mn0.55Ni0.15Co0.1O2/graphite full cells in electrolytes with and without 1 wt. % BTMSC.

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Figure 1. LSV profiles of Pt electrode in the baseline and BTMSC-containing electrolytes (a); optimized structures and the corresponding oxidation potential (V, vs. Li /Li+) of BTMSC, EC, DEC, EMC (b); calculated bond length and corresponding optimized structures of BTMSC (c).

27



Figure 2. Optimized structures and adiabatic ionization energy (AIE, KJ mol-1) of X-PF6- (a), BTMSC-X (b) and BTMSC-PF6--X (c) before and after one electron oxidation Optimized structures and the relative binding energies (Eb, KJ mol-1) of X-Li+ (d). X = EC, EMC, DEC, and BTMSC.

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Figure 3. Cycling stability and coulombic efficiency (a), the initial charge-discharge profiles (b), chronoamperometric profiles at 4.8 V (c), and self-discharge profiles after three charge-discharge cycles (d) for LLO/Li coin cells in the baseline and BTMSC-containing electrolytes.

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Figure 4. XRD patterns of LLO before and after 200 cycling (a) and contents of Ni, Co and Mn deposited on the lithium electrode after 200 cycles (b).

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Figure 5. SEM and TEM images of LLO before (a，d) and after 200 cycles in electrolyte without (b，e) and with 1 wt. % BTMSC (c，f).

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Figure 6. XPS spectra of C1s, O1s, F1s, P2p, N1s, and Si2p of LLO after 200 cycles in electrolytes with and without BTMSC.

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Figure 7. 19F NMR spectra of baseline (blank line) and BTMSC-containing electrolytes (red line ) after storing for 60 hours (a, b) at 55℃ and adding 1 vol. % H2O for 12 hours (c, d) at room temperature.

33



Figure 8. The first and second charging/discharging curves in electrolytes without (a) and with (b) BTMSC, cycling stability (c) and coulombic efficiency (d) for graphite/Li cells in electrolytes with and without BTMSC; Cycling stability (e) and coulombic efficiency (f) of LLO/graphite full cells in electrolytes with and without 1 wt. % BTMSC.

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Graphical abstract

35


Stabilizing a High-Voltage Lithium-Rich Layered Oxide Cathode with a

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