Improving Electrochemical Performances of Li-Rich Layered Mn

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Improving Electrochemical Performances of Li-rich Layered Mnbased Oxide Cathodes through K2Cr2O7 Solution Treatment Xiaohui Zhang, Shuang Cao, Ruizhi Yu, Cheng Li, Yan Huang, Yu Wang, Xianyou Wang, and Gairong Chen ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.8b02178 • Publication Date (Web): 08 Jan 2019 Downloaded from http://pubs.acs.org on January 13, 2019

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ACS Applied Energy Materials

Figure 1. SEM images of (a, e) LMNCO, (b, f) LMNCO-0.05M, (c, g) LMNCO-0.1M, and (d, h) LMNCO-0.2M samples.

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Figure 2. (a) XRD patterns of pristine LMNCO and treated materials such as LMNCO-0.05M, LMNCO-0.1M, and LMNCO-0.2M; (b-d) Enlarged regions; (e) Raman spectra of pristine LMNCO and treated with 0.1 mol L-1 K2Cr2O7 of LMNCO-0.1M materials; the crystal structures of (f) layered LiMO2, (g) monoclinic Li2MnO3, and (h) spinel LiM2O4; the XRD patterns and Rietveld analysis plots of (i) LMNCO and (j) LMNCO-0.1M materials.


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Figure 3. TEM images, HRTEM of the circled regions and corresponding FFT patterns of (a, c and d) LMNCO, (b, e and f) LMNCO-0.1M samples; (g-j) the elemental mapping of LMNCO-0.1M sample.



Figure 4. (a) XPS survey spectrum and core-level spectra for (b) Mn 2p, (c) Ni 2p, (d) Co 2p, (e) O 1s, (f) Cr 2p of the LMNCO, LMNCO-0.05M, LMNCO-0.1M and LMNCO-0.2M samples.


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Figure 5. (a) Initial charge-discharge profiles of untreated LMNCO and LMNCO treated with 0.05, 0.1 and 0.2 mol L-1 K2Cr2O7 solution at 0.1 C, (b) corresponding dQ/dV profiles, (c) cycle performances at 0.5 C and (d) rate capabilities of four samples.



Figure 6. (a) cycle performances of LMNCO and LMNCO-0.1M samples at 1 C, the charge-discharge curves of (b) LMNCO and (c) LMNCO-0.1M electrodes at specific circles (1st, 25th, 50th, 75th, 100th, 125th and 150th) and corresponding differential capacity versus voltage curves (dQ/dV vs V) of (d) LMNCO and (e) LMNCO-0.1M at 1 C.


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Figure 7. The GITT curves of (a) LMNCO and (b) LMNCO-0.1M electrodes versus time

between 2.0 V and 4.6 V; (c) dE/dx, (d) dE/dt1/2, and (e) the calculated DLi  values for the LMNCO and LMNCO-0.1M electrodes versus the voltage.



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Improving Electrochemical Performances of Li-rich Layered Mn-based Oxide Cathodes through K2Cr2O7 Solution Treatment Xiaohui Zhanga, Shuang Caoa, Ruizhi Yua, Cheng Lia, Yan Huanga, Yu Wanga, Xianyou

Wanga，

Gairong Chenb (a: National Base for International Science & Technology Cooperation, National Local Joint Engineering Laboratory for Key Materials of New Energy Storage Battery, Hunan Province Key Laboratory of Electrochemical Energy Storage & Conversion, School of Chemistry, Xiangtan University, Xiangtan 411105, Hunan, China b: Chemistry & Chemical Engineering School, Xinxiang College, Henan 453003, China)

ABSTRACT: The chemical pre-treatment is usually an efficient strategy for improving the electrochemical performance and reducing the voltage fading of the Li-rich Mn-based materials. Herein the different concentration K2Cr2O7 solution pre-treatment and subsequent annealing processes are applied in the modification of the layered porous Li-rich Mn-based Li1.2Mn0.54Ni0.13Co0.13O2. The changes of the structure and electrochemical properties of the sample before/after modification are investigated by Raman spectrometer, transmission electron microscopy, powder X-ray diffractometer and Galvanostatic charge/discharge tests. It has been found that K2Cr2O7 solution treatment and subsequent annealing can not only form the spinel phase on the surface of the layered porous Li-rich Mn-based particles, but also lead Cr doping on the surface of Li1.2Mn0.54Ni0.13Co0.13O2, and thus distinctly improving the cyclic stability and the rate capability of the sample. Especially, the layered porous Li-rich Mn-based Li1.2Mn0.54Ni0.13Co0.13O2 after 0.1 mol L-1 K2Cr2O7 treatment represents a distinctly high initial Coulombic efficiency of 91%, the enhanced rate capability of 129.3 mAh g−1 even at a rate of 10 C and the good cyclic stability with capacity retention of 86% after 200 cycles at a rate of 0.5 C. KEYWORDS: Li-rich cathode; oxidant treating; spinel phase; Cr doping; cyclic stability

Corresponding

author: Xianyou Wang, Tel: +86 731 58293377; E-mail: [email protected] 1


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INTRODUCTION Because of the growing environmental pollution and global warming caused by the overuse of fossil fuels, people are urgently looking for the green and renewable energy resources.1 Lithium-ion batteries (LIBs) have been received great attention as one of the most appropriate energy storage device for electric vehicles and renewable energy storage grids with a pretty long cyclic life and high energy density.2-4 However, as the increment of requirements to electrify transportation, portable electronic devices and smart grids, the great attention is now being payed to raise the performance of LIBs (e.g., energy density, power density, and cyclic life), and which is mainly depends on the electrode materials.5,

6

Hence, it is necessary to

unremittingly enhance the research in electrode materials especially cathode materials, which is predominant factor in restricting the performance of LIBs.7 At the present times, the common cathode materials principally encompass layered LiCoO2, olivine LiFePO4, spinel LiMn2O4, as well as layered LiNi1-2yCoyMnyO2, while these materials still undergo low specific capacity and voltage plateaus, which hinder their utilization in LIBs as the energy storage devices with high energy density.8-10 Recently, Li and Mn-rich layered oxides (LLOs), typically formulated as xLi2MnO3∙(1-x)LiMO2 (TM =Ni, Co, Mn, etc.), can provide exceptionally high reversible capacity (>250 mA h g-1) and wide voltage window (2.0–4.8 V), which have drawn great attention and have been regarded as cathodic candidate for transportation applications, such as EV, HEV and PHEV.2, 11, 12 However, LLOs still exist several issues. For instance, the migration of transition metal ions and irreversible phase transformation become more and more severe during the cycle, which will cause voltage decay and a rapid decrease in energy density.13,

14

Recently, there are many researches that have been made to mitigate

voltage decay. And doping with metal ions has been recognized as an effective method to stabilize the structure of the material. For instance, Nayak et al. reported that Mg2+ doped was beneficial in stabilizing the capacity and discharge voltage of Li-rich materials.15 Yan et al. adopted nucleation and post-solvothermal method to synthesize Al doped Li1.45Al0.05Mn0.675Ni0.1675Co0.1675O2, which could enhance the 2



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electron conductivity of layered material.16 In our previous work, besides, lanthanum doping was introduced into Mn site of lithium-rich layered oxide, which delivered outstanding electrochemical performance.17 In addition, Li-rich layered oxides with antimony doping and nanofiber architecture was synthesized, which possessed outstanding electrochemical properties.18 It is well known that LLOs exist a voltage plateau around 4.5 V corresponding to the activation of Li2MnO3 during the initial charge process. And the ultrahigh capacity of LLOs is usually associated with the participation of reversible anionic redox in the process of activation.19, 20 However, there is irreversible loss of oxygen in the electrochemical activation process of Li2MnO3, which not only results in large irreversible capacity loss, but also is related to surface structural transformation.21, 22 It has been reported that a chemical pre-treated method was a somewhat desirable strategy to reduce the large irreversible capacity loss. For example, Pan et al. adopted Na2S2O8 solution treatment and annealing to successfully form spinel phase on the surface of lithium-rich layered cathode material which delivered high initial coulombic

efficiency

of

93.2%.23

Hu

et

al.

used

NH4F

to

pretreat

Li[Li0.2Ni0.13Co0.13Mn0.54]O2 cathodes materials and obtained ultrahigh initial coulombic efficiency of 102.2%.13 In this study, K2Cr2O7 is used to pretreat the porous Li-rich layered Li[Li0.2Ni0.13Co0.13Mn0.54]O2. Since K2Cr2O7 is a strong oxidant similar to Na2S2O8, it can oxidize the part lattice oxygen to O 22 - species, while the O 22 - species will turn to O2 and release during annealing, which maybe cause some changes of crystal structure. Hence, a thin spinel phase layer can form on the surface of the materials after K2Cr2O7 solution treatment and calcination. The formed spinel phase with 3D Li+ channels can promote Li+ diffusion, moreover, the release of O2 from the surface of the material during cycling process can be suppressed, which can improve the rate performance of the material.13 Furthermore, differing from the reagents using in chemical pre-treated method, K2Cr2O7 treatment and subsequent annealing process can result in the Cr doping on the surface of particles, which can suppress lattice 3


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distortion during insertion and extraction of lithium, enhance surface structural stability and reduce the voltage decay.24-26 By the combination of surface treatment and doping, the changes in microstructure and electrochemical performance of Li[Li0.2Ni0.13Co0.13Mn0.54]O2 are investigated in detail.

EXPERIMENTAL SECTION Preparation of layered porous Li1.2Mn0.54Ni0.13Co0.13O2 (LMNCO). In order to composite the layered porous LMNCO, solvothermal method and high-temperature calcination were adopted. In a typical process of composition, 30 mL ethylene glycol was added to each of the two beakers. Secondly, analytical-grade chemicals include MnCl2·4H2O, NiCl2·6H2O, and CoCl2·6H2O (the molar ratio of them was 4: 1: 1) were added into one of the beakers and 18 mmol NH4HCO3 was added into the other one. Stirred continuously till the chloride salts and NH4HCO3 was completely dissolved, respectively. Mixed evenly chloride salts and NH4HCO3 solution and then the mixture was transferred into a 100 mL Teflon ware. Next, it was sealed in an autoclave and heated at 180 °C for 20 h. Then the obtained suspension after solvothermal reaction was filtrated and washed with deionized water and ethanol several times to end up with pink precursor powder. The filtered precursor powder was dried at 80 °C overnight, subsequently, the precursor powder after drying was calcined at 500 °C for 6 h to get oxide precursor. In the end, the obtained oxide precursor and Li2CO3 were uniformly ground with a molar ratio of Li: M (M= Mn, Ni, Co) = 1.50. The well-mixed powder was first preheated at 500 °C for 6 h and then calcined at 800 °C for 12 h in air to obtain the LMNCO. Then the synthesized LMNCO powders (0.4 g) were added into K2Cr2O7 solutions (0.05/0.1/0.2 mol L-1) and were continuously stirred 0.5 h, afterwards, the mixture was dried in an oven at 80°C after filtering and washing with distilled water. At last, the pretreated powders were calcined in a muffle furnace at 500°C for 3 h in air to obtain LMNCO, LMNCO-0.05M, LMNCO-0.1M, and LMNCO-0.2M materials respectively. Materials Characterizations. A field-emission scanning electron microscopy 4



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(FESEM, sihmaHD-01-61) was applied to view the morphology and size of untreated LMNCO and treated LMNCO materials. The crystallography phase of four samples was record by an X-ray Polycrytalling diffractometer (XRD, D8 Advance, Bruker) which is equipped with Cu Kα radiation. A Raman spectrometer (Thermo Scientific DXRxi) was applied to obtain Raman scattering and Nd-line was used as laser source. A transmission electron microscope (TEM, HT-7700, Hitachi) carried an energy-dispersive X-ray spectroscopy (EDS) detector was applied to characterize the detailed structural characterizations and elemental distribution of samples. Moreover, X-ray photoelectron spectrometer (XPS, ESCALAB 250, ThermoFisher SCIENTIFIC) was applied to analyze the surface elemental valence and chemical compositions of samples. Electrochemical Measurements. To manufacture the positive electrodes for electrochemical measurements, 80 wt% active material (LMNCO, LMNCO-0.05M, LMNCO-0.1M, and LMNCO-0.2M), 10 wt% PVDF binder (polyvinylidene fluoride) and

10

wt%

conductive

super

P

were

added

into

solvent

of

NMP

(N-methyl-2-pyrrolidone) to slurry and then it was evenly smeared on an aluminum foil current collector. After drying in vacuum oven overnight at 110°C to remove NMP and moisture, the aluminum foil was punched as discs with diameter of 10 mm. In a general way, the loading level of active material on disc was maintained around 5 mg·cm−2. In the next moment, the assembly of CR2025 coin cell was carried out in a glovebox filled with argon, in which Li metal was used as the anode, a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio1:1,) dissolved 1 mol·L−1 LiPF6 acted as the electrolyte, besides, porous membrane (Celgard 2325) was used as the separator. In order to investigate the electrochemical performance of pristine and treated materials, Galvanostatic charge and discharge tests were performed by a Neware (CT-3008) at room temperature and the voltage window of tests were between 2.0 and 4.6 V (vs Li+/Li).

RESULTS AND DISCUSSION 5


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The morphologies of the pristine material and the materials treated with three different concentration K2Cr2O7 solutions are characterized by a field-emission scanning electron microscopy (FESEM), which are displayed in Figure 1. As being seen, the four samples possess a semblable spherical morphology and the average size of four samples is about 1.2 μm, which verifies that treating by K2Cr2O7 solution and calcining process will not change the morphology and size of LMNCO.

Figure 1. SEM images of (a, e) LMNCO, (b, f) LMNCO-0.05M, (c, g) LMNCO-0.1M, and (d, h) LMNCO-0.2M samples.

The crystal structures of LMNCO, LMNCO-0.05M, LMNCO-0.1M, and LMNCO-0.2M samples are investigated by XRD, and the XRD patterns are shown in Figure 2a-2d. The main diffraction peaks of the pristine and treated materials are belong to hexagonal α-NaFeO2 structure with R3m space group.25,

27

In addition,

there are some weak superlattice diffraction peaks in the 2θ range of 20−25° which can be indexed as the (020) and ( 111 ) planes of monoclinic Li2MnO3 with C2/m symmetry and are characteristic of lithium-rich layered oxides.28, 29 Besides, several shoulder peaks (marked aside with rhombus) can be distinguished, which are assigned to spinel-type structure with space group

Fd3m

for LMNCO-0.1M and

LMNCO-0.2M samples in Figure 2b-2d.30 Moreover, the (003) peak gradually shifts to lower 2θ angle as the concentration of K2Cr2O7 solution increases in Figure 2b, which may be owing to the enlarged Li+ slab caused by surface spinel phase and Cr doping.31, 32 There is no peak of impurities, indicating that Cr is successfully inserted 6



into the lattice on the surface of materials rather than in other impure phases. Figure 2e shows the Raman spectra of the pristine and treated with 0.1 mol/L K2Cr2O7 materials. There are two broad peaks around 476 and 590 cm−1 in two materials, which are on behalf of the bending Eg and stretching A1g modes of the layered R 3m structure, respectively.33 In addition, some weak peaks between 300 cm−1 and 450 cm−1 belonging to monoclinic Li2MnO3 are observed. Furthermore, an shoulder band at 625 cm−1 appears and Raman peak around 590 cm−1 is blue shifted toward a short wave in the LMNCO-0.1M sample, which is associated with the formation of spinel LiM2O4 phase (M=Mn, Ni).30, 34 When pretreated with K2Cr2O7 solution, the part lattice oxygen on the surface of particles is oxidized by K2Cr2O7 to generate

O 22 - species and Cr3+ forms due to reduction at the same time. In the

following process of calcination, the generated

O 22 - species is unstable, which is

easily to converted to O2 and to release in process of calcination which maybe cause some changes of crystal structure and form spinel phase on the surface, meanwhile, Cr can be inserted into the lattice near the surface.35 The full Rietveld refinement of the XRD data are used to further analyze the crystalline structural details of the pristine and treated with 0.1 mol L-1 K2Cr2O7 materials, which are based on LiMO2 ( R3m ) and Li2MnO3 (C2/m) mixture phase, while for LMNCO-0.1M sample, additional LiM2O4 ( Fd3m ) phase is taken into account. The Rietveld refinement XRD data are shown in Figure 2i and 2g, and calculated lattice parameters are listed in Table 1. As can be seen, the contents of

R3m , C2/m and Fd3m phases for LMNCO-0.1 are about 74.62, 23.02, and 2.36%. Compared with LMNCO, the decrease in the contents of C2/m phase and the corresponding increase of Fd3m phase for LMNCO-0.1 mean that the formation of

Fd3m phase is mainly related with C2/m phase. The refinement results indicate that Cr is successfully inserted into the lattice, which may be because Cr3+ with an ionic radius of 0.0615 nm is larger than that of Mn4+ and Co3+ (0.053 and 0.0545 nm).26, 36 7


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Furthermore, the lattice parameters, especially the value of c increases, which indicate that the interslab spacing expands after treating with K2Cr2O7. Apparently, the expanding interslab spacing is conducive to Li+ diffusion and the surface doping can suppress the lattice distortion which is beneficial to enhance the stability of surface structure.25

8



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Figure 2. (a) XRD patterns of pristine LMNCO and treated materials such as LMNCO-0.05M, LMNCO-0.1M, and LMNCO-0.2M; (b-d) Enlarged regions; (e) Raman spectra of pristine LMNCO and treated with 0.1 mol L-1 K2Cr2O7 of LMNCO-0.1M materials; the crystal structures of (f) layered LiMO2, (g) monoclinic Li2MnO3, and (h) spinel LiM2O4; the XRD patterns and Rietveld analysis plots of (i) LMNCO and (j) LMNCO-0.1M materials. Table 1. Refined crystallographic parameters of LMNCO and LMNCO-0.1M materials

Lattice parameter

R3m phase

C2/m phase

Fd3m phase

LMNCO

LMNCO-0.1M

a

2.8496

2.8497

c

14.229

14.233

a

4.934

4.940

b

8.544

8.542

c

5.029

5.036

a

8.2541

Ni in Li (3a)

5.64%

Cr in Metal layer Percentage composition

5.09% 3.05%

R3m

73.401%

74.616%

26.599%

23.020%

phase C2/m phase 2.364%

Fd3m phase Reliability factors

Rwp

4.06%

3.66%

Rp

3.17%

2.91%

χ2

1.15%

1.06%

High-resolution TEM (HRTEM) examination is applied to provide the detailed structural information on the LMNCO and LMNCO-0.1M materials, and the TEM images and the corresponding Fast Fourier transform (FFT) patterns are shown in Figure 3. In Figure 3a, 3c and 3d of LMNCO sample, it can be noticed three sets of 9


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lattice spacing of 0.408, 0.366 nm and 0.317 nm, which match well with ( 111 ), (111) and (022) planes of monoclinic Li2MnO3, respectively. As for LMNCO-0.1M samples in Figure 3b, 3e and 3f, aside from (020), (200) and (220) planes of Li2MnO3 with corresponding lattice spacing of 0.426, 0.243 nm and 0.211 nm, there are new lattice spacing of 0.471 and 0.204 nm, which can be indexed to (111) and (400) planes of spinel LiM2O4 phase with Fd3m space group. In addition, the elemental mapping of LMNCO-0.1M sample in Figure 3j indicates that element of Cr exists. In addition, the element of Cr is evenly distributed throughout the secondary particles, and the result of which and the above analysis of XRD show that Cr are doped into the lattice of LMNCO.

Figure 3. TEM images, HRTEM of the circled regions and corresponding FFT patterns of (a, c and d) LMNCO, (b, e and f) LMNCO-0.1M samples; (g-j) the elemental mapping of LMNCO-0.1M sample. 10



To investigate the surface elemental valence and chemical compositions of four samples, XPS measurement is applied and the corresponding spectra of four samples are compared in Figure 4. Moreover, there is a Cr 2p for the treated materials, which confirms the presence of Cr element. The binding energies of all samples are corrected by the reference of C 1s peak at 284.7 eV. As seen in Figure 4b-4d, the binding energies of Mn 2p3/2 Ni 2p3/2 and Co 2p3/2 fit well with the Mn4+, Ni2+, and Co3+,37-39 and the treatment of K2Cr2O7 causes little change in the positions of peaks of the Mn, Ni, and Co, indicating that Cr tends to substitute for the 3a site in LMO2 to maintain charge balance of the system.40 As for the O 1s spectra in Fig. 4e, there are two peaks, one of which is at 529.6 eV belonging to O2- anions in crystalline network and the other is at 531.0 eV associated with surface species.41 The binding energies of Cr 2p3/2 and Cr 2p1/2 are about 576.80 and 586.35 eV, respectively, matching well with Cr3+.42

Figure 4. (a) XPS survey spectrum and core-level spectra for (b) Mn 2p, (c) Ni 2p, (d) Co 2p, (e) O 1s, (f) Cr 2p of the LMNCO, LMNCO-0.05M, LMNCO-0.1M and LMNCO-0.2M samples.

The initial charge-discharge curves of LMNCO and LMNCO treated with 0.05, 0.1 and 0.2 mol L-1 K2Cr2O7 solutions at 0.1 C (1 C = 200 mA g-1) between 2.0 and 11


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4.6 V as well as corresponding dQ/dV profiles are displayed in Figure 5a and 5b. It is easy to see that the initial charge-discharge feature of materials treated with K2Cr2O7 solution is similar to the pristine material, which coincides with representative profile of Li-rich layered cathode materials. There is a long platform around 4.5 V, which is linked to the activation of Li2MnO3 component accompanied by the irreversible oxygen release.43,

44

However, the platform around 4.5 V of samples treated with

K2Cr2O7 solution becomes shorter and a slight spinel voltage platform around 2.7 V forms (except LMNCO-0.05M) after treating with 0.1 and 0.2 mol L-1 K2Cr2O7 solution, suggesting the generation of chemical de-lithiation from the Li2MnO3 component and phase transformation after calcining. The generated spinel plateau can provide excess capacity which will be conducive to improve initial coulombic efficiency.13 The initial electrochemical data of LMNCO, LMNCO-0.05M, LMNCO-0.1M and LMNCO-0.2M samples at 0.1 C are shown in Table 2. It is pretty obvious that the initial coulombic efficiencies of treated materials are higher than that of the pristine material, which are 83, 86, 91 and 93% for LMNCO, LMNCO-0.05M, LMNCO-0.1M and LMNCO-0.2M, respectively. The cycling performances of untreated and treated samples at the rate of 0.5 C are displayed in Figure 5c. It is easy to see that the capacity retentions of the pretreated materials are superior to pristine one, the discharge capacity and capacity retention after 200 cycles at 0.5 C are 224.3 and 73%, 236.2 and 79%, 252.2 and 86% as well as 245.6 and 81% for LMNCO, LMNCO-0.05M, LMNCO-0.1M and LMNCO-0.2M, respectively. The improvement in cycling performances may be ascribed to the Cr surface doping, which can stabilize the surface structure of material. Apart from cycling performance, the rate capabilities of treated materials are also better than pristine materials, especially LMNCO-0.1M sample, which delivers a discharge capacity of 129.4 mAh g−1 at 10 C, obviously higher than LMNCO with a discharge capacity of 81.5 mAh g−1 at 10 C. The improvement in rate capability may mainly be due to the generation of spinel LiM2O4 phase with 3D Li+ diffusion channels and the expanding interslab spacing, which can obviously enhance Li+ diffusion rate. 12



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Figure 5. (a) Initial charge-discharge profiles of untreated LMNCO and LMNCO treated with 0.05, 0.1 and 0.2 mol L-1 K2Cr2O7 solution at 0.1 C, (b) corresponding dQ/dV profiles, (c) cycle performances at 0.5 C and (d) rate capabilities of four samples. Table 2. The initial electrochemical data at 0.1 C of LMNCO, LMNCO-0.05M, LMNCO-0.1M and LMNCO-0.2M samples

sample

Initial charge

Initial discharge

Irreversible

Coulombic

capacity

capacity (mAh

capacity loss

efficiency

(mAh g−1)

g−1)

(mAh g−1)

13


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LMNCO

348.9

290.8

58.1

83%

LMNCO-0.05M

337.5

289.4

48.1

86%

LMNCO-0.1M

315.8

286.8

29

91%

LMNCO-0.2M

302.8

282.3

20.5

93%

In addition, the cycle performances of LMNCO and LMNCO-0.1M samples after cycling 150 times at 1 C are displayed in Figure 6. As shown in Figure 6a, LMNCO-0.1M sample displays a discharge capacity of 236.1mAh g−1 and capacity retention of 78%, while the discharge capacity and capacity retention of LMNCO are 217.8mAh g−1 and 64%. The charge-discharge curves at 1st, 25th, 50th, 75th, 100th, 125th and 150th and corresponding differential capacity (dQ/dV) versus voltage curves at the rate of 1 C for pristine LMNCO and treated LMNCO-0.1M are shown in Figure 6b-6e. The Mn4+/Mn3+ reduction peak (Peak 1) of LMNCO-0.1M gradually shifts to 2.8 V during 150 cycles, while the Peak 1 of LMNCO rapidly decreases from 3.08 to 2.56 V, as shown in Figure 6d and 6e. Generally speaking, the lower shift of cathodic peak between 2.5 and 3.4 V is relative to the reduction of Mn4+/Mn3+,41 which is related with structural transformation from layered

R 3m

to spinel and cubic

rock-salt phases. The disordering rock-salt phase has an adverse effect on lithium diffusion because of higher activation energy and barrier produced by transition metal migrating in lithium layer, which may eventually cause capacity fading, voltage decay and severe polarization.45,

46

However, the shifts of the treated materials have been

obviously mitigated, which may be attributed to surface doping of Cr to promote the stability of surface structure.25

14



Figure 6. (a) cycle performances of LMNCO and LMNCO-0.1M samples at 1 C, the charge-discharge curves of (b) LMNCO and (c) LMNCO-0.1M electrodes at specific circles (1st, 25th, 50th, 75th, 100th, 125th and 150th) and corresponding differential capacity versus voltage curves (dQ/dV vs V) of (d) LMNCO and (e) LMNCO-0.1M at 1 C.

To further investigate the change in electrochemical performance caused by K2Cr2O7 solution treating and calcination, Galvanostatic intermittent titration technique (GITT) test is applied. GITT test is a dependable technology that can be used to assess Li+ chemical diffusion. Besides, a formula on the basis of Fick’s second

15


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law is used to calculate the Li+ chemical diffusion coefficient ( DLi  , cm2 s-1),47 which is shown below Equ.1: 2

D Li



2

L2 4  V   dE dx   I 0 m     t , D Li π  FS   dE / dt 1 / 2 

(1)

Where I0 is on behalf of the applied current, the unit of which is amperes (A); Vm (cm3 mol-1) refers to the molar volume deducing from crystallographic data of compound; F (C mol-1) stands for the Faraday constant; S (cm2) is the surface area of the electrode; and L (cm) represents the length of lithium diffusion; The values of dE/dx are determined from the Galvanostatic titration curve (dE/dx ≈ ∆E/∆x), which represents the slope of the coulometric titration curve; dE/dt1/2 represents the slope of the E versus square root of time curve.48 The LMNCO and LMNCO-0.1M electrodes were first activated at 0.05 C, then GITT test of LMNCO and LMNCO-0.1M electrodes was performed at 0.1 C between 2.0 and 4.6 V and the corresponding GITT patterns are shown in Figure 7. The plots of dE/dx and dE/dt1/2 versus the voltage in charge process are shown in Figure 7c and 7d. The DLi  is calculated based on the data from GITT tests and the above formula, and the corresponding pattern is shown in Figure 7e. It is clear that DLi  for the LMNCO-0.1M cell is much higher than that of the LMNCO cell, and the DLi  of LMNCO-0.1M cell fluctuates on a constant value of 1.44 × 10−10 cm2·s−1 between 3.8 V to 4.4 V, while that of LMNCO cell is around 6.57 × 10−11 cm2·s−1. The findings reveal that the rate performance of LMNCO-0.1M sample is superior to LMNCO, which can mainly be attributed to action of spinel LiM2O4 phase on the surface of the material and the expansion of interslab spacing.

16



Figure 7. The GITT curves of (a) LMNCO and (b) LMNCO-0.1M electrodes versus time

between 2.0 V and 4.6 V; (c) dE/dx, (d) dE/dt1/2, and (e) the calculated DLi  values for the LMNCO and LMNCO-0.1M electrodes versus the voltage.

CONCLUSIONS In summary, the porous layered Li-rich Mn-based oxide (LMNCO) is pretreated with different concentrations of K2Cr2O7 and calcined, which can results in the introduction of the thin spinel phase layer and Cr doping on the surface of materials. Due to combination action of the spinel phase with 3D Li+ channels and surface doping, the electrochemical performances of the material were obviously improved. Especially, the layered Li-rich Mn-based oxide treated with 0.1 mol L-1 K2Cr2O7 17


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solution showed an excellent electrochemical performance, which delivers initial discharge capacity of 286.8 mAh g−1 at 0.1 C with coulombic efficiencies of 91%. Spinel phase with 3D Li+ channels and the expanding interslab spacing can enhance Li+ diffusion rate, and the material treated with 0.1 mol L-1 K2Cr2O7 possesses higher Li+ chemical diffusion coefficient of 1.44 × 10−10 cm2·s−1 and better rate capability of 129.3 mAh g−1 at 10 C than that of pristine material (6.57 × 10−11 cm2·s−1 and 81.5 mAh g−1 at 10 C). Furthermore, Cr doping can further stabilize the surface structure of material in the cycle process, and hence the material treated with 0.1 mol L-1 K2Cr2O7 has much better capacity retention of 86% at 0.5 C after 200 cycles and the mitigated voltage decay at 1 C after 150 cycles compared to untreated material.

ACKNOWLEDGMENTS We acknowledge support from the Natural Science Foundation of Hunan Province (Nos. 2015JJ2137 and 2015JJ6103), Hunan Provincial Innovation Foundation for Postgraduate (No. CX2016B229), and Key Project of Strategic New Industry of Hunan Province (Nos. 2016GK4030 and 2016GK4005). REFERENCES (1) Xiong, D. Li, X. Bai, Z. Lu, S. Recent Advances in Layered Ti3C2Tx MXene for Electrochemical Energy Storage. Small 2018, 14, 1703419. (2) Nayak, P. K.; Erickson, E. M.; Schipper, F.; Penki, T. R.; Munichandraiah, N.; Adelhelm, P.; Sclar, H.; Amalraj, F.; Markovsky, B.; Aurbach, D. Review on Challenges and Recent Advances in the Electrochemical Performance of High Capacity Li- and Mn-Rich Cathode Materials for Li-Ion Batteries. Adv. Energy Mater. 2018, 8, 1702397. (3) Deng, M. Li, S. Hong, W. Jiang, Y. Xu, W. Shuai, H. Zou, G. Hu, Y. Hou, H. Wang, W. Ji, X. Octahedral Sb2O3 as high-performance anode for lithium and sodium storage. Mater. Chem. Phys. 2019, 223: 46-52. 18



(4) Hou, H. Banks, C.E. Jing, M. Zhang, Y. Ji, X. Carbon Quantum Dots and Their Derivative 3D Porous Carbon Frameworks for Sodium-Ion Batteries with Ultralong Cycle Life. Adv. Mater. 2015, 27, 7861-7866. (5) Hy, S.; Liu, H.; Zhang, M.; Qian, D.; Hwang, B.-J.; Meng, Y. S. Performance and design considerations for lithium excess layered oxide positive electrode materials for lithium ion batteries. Energy Environ. Sci. 2016, 9, 1931-1954. (6) Xiao, W. Wang, J. Fan, L. Zhang, J. Li, X. Recent Advances in Li1+xAlxTi2−x(PO4)3 Solid-State Electrolyte for Safe Lithium Batteries. Energy Storage Mater. 2018. (7) Gong, Z.; Yang, Y. Recent advances in the research of polyanion-type cathode materials for Li-ion batteries. Energy Environ. Sci. 2011, 4, 3223. (8) Wang, G.; Yi, L.; Yu, R.; Wang, X.; Wang, Y.; Liu, Z.; Wu, B.; Liu, M.; Zhang, X.; Yang, X.; Xiong, X.; Liu, M. Li1.2Ni0.13Co0.13Mn0.54O2 with Controllable Morphology and Size for High Performance Lithium-Ion Batteries. ACS Appl. Mater. Inter. 2017, 9, 25358-25368. (9) Xu, Q.; Lian, Q.; Wu, Y.; Ma, C.; Tan, P.; Xia, Q.; Zhang, J.; Ivey, D. G.; Wei, W. Li+-conductive Li2SiO3 stabilized Li-rich layered oxide with an in situ formed spinel nano-coating layer: toward enhanced electrochemical performance for lithium-ion batteries. RSC Adv. 2016, 6, 34245-34253. (10) Thackeray, M. M.; Wolverton, C.; Isaacs, E. D. Electrical energy storage for transportation—approaching the limits of, and going beyond, lithium-ion batteries. Energy Environ. Sci. 2012, 5, 7854. (11) Li, B.; Yan, H.; Ma, J.; Yu, P.; Xia, D.; Huang, W.F.; Chu, W.H.; Wu, Z. Manipulating 19


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 Electronic Structure of Li-Rich Manganese-Based Oxide Using Polyanions: Towards Better Electrochemical Performance. Adv. Funct. Mater. 2014, 24, 5112-5118. (12) Luo, K.; Roberts, M. R.; Hao, R.; Guerrini, N.; Liberti, E.; Allen, C. S.; Kirkland, A. I.; Bruce, P. G. One-Pot Synthesis of Lithium-Rich Cathode Material with Hierarchical Morphology. Nano Lett. 2016, 16, 7503-7508. (13) Hu, X.; Guo, H.; Wang, J.; Wang, Z.; Li, X.; Hu, Q.; Peng, W. Structural and electrochemical

characterization

of

NH4F-pretreated

lithium-rich

layered

Li[Li0.2Ni0.13Co0.13Mn0.54]O2 cathodes for lithium-ion batteries. Ceram. Int. 2018, 44, 14370-14376. (14) Hy, S.; Felix, F.; Rick, J.; Su, W.-N.; Hwang, B. J. Direct in situ observation of Li2O evolution on Li-rich high-capacity cathode material, Li[NixLi(1-2x)/3Mn(2-x)/3]O2 (0≤ x ≤0.5). J. Am. Chem. Soc. 2014, 136, 999-1007. (15) Nayak, P. K.; Grinblat, J.; Levi, E.; Levi, M.; Markovsky, B.; Aurbach, D. Understanding the influence of Mg doping for the stabilization of capacity and higher discharge voltage of Li- and Mn-rich cathodes for Li-ion batteries, Phys. Chem. Chem. Phys. 2017, 19, 6142-6152. (16) Yan, W.; Xie, Y.; Jiang, J.; Sun, D.; Ma, X.; Lan, Z.; Jin, Y. Enhanced Rate Performance of Al-Doped Li-Rich Layered Cathode Material via Nucleation and Post-solvothermal Method. ACS Sustainable Chem. Eng. 2018, 6, 4625-4632. (17) Yu, R.; Wang, G.; Liu, M.; Zhang, X.; Wang, X.; Shu, H.; Yang, X.; Huang, W. Mitigating voltage and capacity fading of lithium-rich layered cathodes by lanthanum doping. J. Power Sources 2016, 335, 65-75. 20



(18) Yu, R.; Zhang, Z.; Jamil, S.; Chen, J.; Zhang, X.; Wang, X.; Yang, Z.; Shu, H.; Yang, X. Effects of Nanofiber Architecture and Antimony Doping on the Performance of Lithium-Rich Layered Oxides: Enhancing Lithium Diffusivity and Lattice Oxygen Stability. ACS Appl. Mater. Inter. 2018, 10, 16561-16571. (19) Perez, A. J.; Jacquet, Q.; Batuk, D.; Iadecola, A.; Saubanère, M.; Rousse, G.; Larcher, D.; Vezin, H.; Doublet, M.-L.; Tarascon, J.-M.; Approaching the limits of cationic and anionic electrochemical activity with the Li-rich layered rocksalt Li3IrO4. Nat. Energy 2017, 2, 954-962. (20) Qiu, B.; Zhang, M.; Xia, Y.; Liu, Z.; Meng, Y. S. Understanding and Controlling Anionic Electrochemical Activity in High-Capacity Oxides for Next Generation Li-Ion Batteries. Chem. Mater. 2017, 29, 908-915. (21) Liu, S.; Liu, Z.; Shen, X.; Li, W.; Gao, Y.; Banis, M. N.; Li, M.; Chen, K.; Zhu, L.; Yu, R.; Wang, Z.; Sun, X.; Lu, G.; Kong, Q.; Bai, X.; Chen, L. Surface Doping to Enhance Structural Integrity and Performance of Li-Rich Layered Oxide. Adv. Energy Mater. 2018, 8, 1802105. (22) Clément, R. J.; Kitchaev, D.;Lee, J.; Ceder, G. Short-range order and unusual modes of nickel redox in a fluorine-substituted disordered rocksalt oxide lithium-ion cathode. Chem. Mater. 2018, 30, 6945-6956. (23) Pan, L.; Xia, Y.; Qiu, B.; Zhao, H.; Guo, H.; Jia, K.; Gu, Q.; Liu, Z. Synthesis and electrochemical performance of micro-sized Li-rich layered cathode material for Lithium-ion batteries. Electrochim. Acta 2016, 211, 507-514. (24) Song, B.; Zhou, C.; Wang, H.; Liu, H.; Liu, Z.; Lai, M.; Lu, L. Advances in Sustain 21


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


Stable Voltage of Cr-Doped Li-Rich Layered Cathodes for Lithium Ion Batteries. J. Electrochem. Soc. 2014, 161, A1723-A1730. (25) Pang, W.; Lin, H.-F.; Peterson, V. K.; Lu, C.-Z.; Liu, C.-E.; Liao, S.-C.; Chen, J.-M. Effects of Fluorine and Chromium Doping on the Performance of Lithium-Rich Li1+xMO2 (M = Ni, Mn, Co) Positive Electrodes. Chem. Mater. 2017, 29, 10299-10311. (26) Lee, E.; Park, J. S.; Wu, T.; Sun, C.-J.; Kim, H.; Stair, P. C.; Lu, J.; Zhou, D.; Johnson, C. S. Role of Cr3+/Cr6+ redox in chromium-substituted Li2MnO3·LiNi1/2Mn1/2O2 layered composite cathodes: electrochemistry and voltage fade. J. Mater. Chem. A 2015, 3, 9915-9924. (27) Chen, S.; Chen, Z.; Xia, M.; Cao, C.; Luo, Y. Toward Alleviating Voltage Decay by Sodium Substitution in Lithium-Rich Manganese-Based Oxide Cathodes. ACS Appl. Energy Mater. 2018, 1, 4065-4074. (28) Matsunaga, T.; Komatsu, H.; Shimoda, K.; Minato, T.; Yonemura, M.; Kamiyama, T.; Kobayashi, S.; Kato, T.; Hirayama, T.; Ikuhara, Y.; Arai, H.; Ukyo, Y.; Uchimoto, Y.; Ogumi, Z. Dependence of Structural Defects in Li2MnO3 on Synthesis Temperature. Chem. Mater. 2016, 28, 4143-4150. (29) Ye, D.; Zeng, G.; Nogita, K.; Ozawa, K.; Hankel, M.; Searles, D. J.; Wang, L. Understanding the Origin of Li2MnO3 Activation in Li-Rich Cathode Materials for Lithium-Ion Batteries. Adv. Funct. Mater. 2015, 25, 7488-7496. (30) Wu, B.; Yang, X.; Jiang, X.; Zhang, Y.; Shu, H.; Gao, P.; Liu, L.; Wang, X. Synchronous Tailoring Surface Structure and Chemical Composition of Li-Rich-Layered Oxide for High-Energy Lithium-Ion Batteries. Adv. Funct. Mater. 2018, 1803392. 22



(31) Feng, X.; Gao, Y.; Ben, L.; Yang, Z.; Wang, Z.; Chen, L. Enhanced electrochemical performance of Ti-doped Li1.2Mn0.54Co0.13Ni0.13O2 for lithium-ion batteries. J. Power Sources 2016, 317, 74-80. (32) Xue, Z.; Qi, X.; Li, L.; li, W.; Xu, L.; Xie, Y.; Lai, X.; Hu, G.; Peng, Z.; Cao, Y.; Du, K. Sodium Doping to Enhance Electrochemical Performance of Overlithiated Oxide Cathode Materials for Li-Ion Batteries via Li/Na Ion-Exchange Method. ACS Appl. Mater. Inter. 2018, 10, 27141-27149. (33) Yu, F.; Que, L.; Wang, Z.; Zhang, Y.; Xue, Y.; Liu, B.; Gu, D. Layered-spinel capped nanotube assembled 3D Li-rich hierarchitectures for high performance Li-ion battery cathodes. J. Mater. Chem. A 2018, 4, 18416-18425. (34) Croy, J.R. Kang, S.-H, Balasubramanian, M. Thackeray, M.M. Novel Cathode Structures from Li2MnO3 Precursors for Li-Ion Batteries. J. Electrochem. Soc. 2011, 12, 580-580. (35) Han, S.; Qiu, B.; Wei, Z.; Xia, Y.; Liu, Z. Surface structural conversion and electrochemical enhancement by heat treatment of chemical pre-delithiation processed lithium-rich layered cathode material. J. Power Sources 2014, 268, 683-691. (36) Li, H.; Guo, H.; Wang, Z.; Wang, J.; Li, X.; Chen, N.; Gui, W. Improving rate capability and decelerating voltage decay of Li-rich layered oxide cathodes by chromium doping. Int. J. Hydrogen Energy 2018, 43, 11109-11119. (37) Duraisamy, S.; Penki, T. R.; Kishore, B.; Barpanda, P.; Nayak, P. K.; Aurbach, D.; Munichandraiah, N. Porous, hollow Li1.2Mn0.53Ni0.13Co0.13O2 microspheres as a positive electrode material for Li-ion batteries. J. Solid State Electrochem. 2016, 21, 437-445. (38) Li, J.; Li, M.; Zhang, L.; Wang, J. General synthesis of xLi2MnO3·(1 − 23


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


x)LiNi1/3Co1/3Mn1/3O2 (x = 1/4, 1/3, and 1/2) hollow microspheres towards enhancing the performance of rechargeable lithium ion batteries. J. Mater. Chem. A 2016, 4, 12442-12450. (39) Liu, W. Li, X. Xiong, D. Hao, Y. Li, J. Kou, H. Yan, B. Li, D. Lu, S. Koo, A. Adair, K. Sun, X. Significantly improving cycling performance of cathodes in lithium ion batteries: the effect of Al2O3 and LiAlO2 coatings on LiNi0.6Co0.2Mn0.2O2. Nano Energy 2018, 44, 111-120. (40) Ding, Z.; Xu, M.; Liu, J.; Huang, Q.; Chen, L.; Wang, P.; Ivey, D.; Wei, W. Understanding the Enhanced Kinetics of Gradient-Chemical-Doped Lithium-Rich Cathode Material. ACS Appl. Mater. Inter. 2017, 9, 20519-20526. (41) Sathiya, M.; Rousse, G.; Ramesha, K.; Laisa, C. P.; Vezin, H.; Sougrati, M. T.; Doublet, M. L.; Foix, D.; Gonbeau, D.; Walker, W.; Prakash, A. S.; Hassine, M. B.; Dupont, L.; Tarascon, J. M. Reversible anionic redox chemistry in high-capacity layered-oxide electrodes. Nat. Mater. 2013, 12, 827-835. (42) Wu, C. Wu, F. Chen, L. Huang, X. X-ray diffraction and X-ray photoelectron spectroscopy analysis of Cr-doped spinel LiMn2O4 for lithium ion batteries. Solid State

Ionics 2002, 152, 335-339. (43) Yu, R.; Zhang, X.; Liu, T.; Yang, L.; Liu, L.; Wang, Y.; Wang, X.; Shu, H.; Yang, X. Spinel/Layered Heterostructured Lithium-Rich Oxide Nanowires as Cathode Material for High-Energy Lithium-Ion Batteries. ACS Appl. Mater. Inter. 2017, 9, 41210-41223. (44) Yu, R. Wang, X. Wang, D. Long, G. Shu, H. Yang, X. Self-assembly synthesis and electrochemical performance of Li1.5Mn0.75Ni0.15Co0.10O2+δ microspheres with multilayer shells. J. Mater. Chem. A 2015, 3, 3120-3129. (45) Oh, P.; Ko, M.; Myeong, S.; Kim, Y.; Cho, J. A Novel Surface Treatment Method and 24



New

Insight

into

Discharge

Voltage

Deterioration

Page 32 of 33

for

High-Performance

0.4Li2MnO3-0.6LiNi1/3Co1/3Mn1/3O2 Cathode Materials. Adv. Energy Mater. 2014, 4, 1400631. (46) Liu, W.; Oh, P.; Liu, X.; Lee, M. J.; Cho, W.; Chae, S.; Kim, Y.; Cho, J. Nickel-rich layered lithium transition-metal oxide for high-energy lithium-ion batteries. Angew. Chem. 2015, 54, 4440-4457. (47) Choi, Y. M.; Pyun, S. I. Determination of electrochemical active area of porous Li1−δCoO2 electrode using the GITT technique. Solid State Ionics 1998, 109, 159-163. (48) Shaju, K.M. Subba Rao, G.V. Chowdari, B.V.R. EIS and GITT studies on oxide cathodes, O2-Li(2/3)+x(Co0.15Mn0.85)O2 (x=0 and 1/3). Electrochim. Acta 2003, 48, 2691-2703.

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Improving Electrochemical Performances of Li-Rich Layered Mn

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