Effect of TiO2 coating on structure and electrochemical performance of LiNi0.6Co0.2Mn0.2O2 cathode material for lithium ion batteries

doi:10.21203/rs.3.rs-4859905/v1

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Effect of TiO₂ coating on structure and electrochemical performance of LiNi_0.6Co_0.2Mn_0.2O₂ cathode material for lithium ion batteries

https://doi.org/10.21203/rs.3.rs-4859905/v1

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Many efforts have been made to improve the electrochemical performance of Ni-rich cathode materials, such as metal ion doping, surface modification, and fabricating nanostructured materials. Here, to enhance the electrochemical performance of the LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cathode, NCM622 was coated by TiO₂ layers through the sol-gel process. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical tests have been applied for material characterizations and electrochemical measurements. Compared with the pristine NCM622 electrode, the cycling stability and rate performance of the TiO₂-coated NCM622 electrodes are significantly improved. Among all TiO₂-coated NCM622, the NCM622 cathode with TiO₂ coating content of 0.5% demonstrats a highest capacity retention of 89.3% and a discharge capacity of 163.9 mAh g^− 1, in contrast to 80.9% and145 mAh g^− 1 for the pristine NCM622 electrode, after 100 cycles at 0.3 C between 3-4.3 V. Under the high cutoff voltage of 4.6 V, the 5 wt% TiO₂-coated.

NCM electrode exhibit better electrochemical properties than bare NCM622 in terms of specific capacity and cyclability, similar to the results measured at a cut-off voltage of 4.3 V. The results prove that TiO₂ modification can lower the polarization of the material, effectively raising the cycling stability rate performance of the battery. It provides a reference path for the further progress of high capacity and stability ternary cathode materials.

LiNi0.6Co0.2Mn0.2O2

TiO2 coating

Lithium ion batteries

Modification

With the increasing consumption of fossil fuels, the development of a green industrial revolution and the use of clean renewable energy to achieve carbon substitution has become an inevitable trend, while the development and promotion of renewable energy is also inseparable from reliable energy storage devices [1]. As a cost-effective energy storage device, rechargeable lithium-ion batteries (LIBs), with the advantages of high energy density, small size, light weight, no memory effect, low self-discharge and long life compared with traditional secondary batteries, they have been widely used in portable electronics and electric vehicles [2–3]. The cathode material plays a crucial role in the electrochemical performance of LIBs, so there has to be developed high discharge specific capacity, high operating voltage, good stability, and low cost cathode material matching high performance LIBs [4–5].

Nickel-rich LiNi_xCo_yMn_zO₂ (NCM, x ≥ 0.6) cathode materials with high specific capacity and lower cost have attracted much attention due to the synergistic effect of Ni, Co, Mn. Among them, LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cathode material possesses moderate Ni content, which has higher specific capacity, better cycling stability, improved safety, lower cost and toxicity [6]. Therefore, it has been considered to be one of the most promising candidates for the high energy and long lifespan LIBs [6–9].

However, the migration of transition metal ions of the nickel-rich layer structure at higher voltages usually leads to its structural degradation, which means the transformation of NCM622 from layered to spinel and rock salt phases during cycling, resulting in poor cycling stability and weak thermal stability [8–9]. In addition, there are side reactions at the interface between NCM622 and electrolyte, which consume active components and reduce reversible capacity, including the dissolution of transition metal ions and the growth of cathode electrolyte interface (CEI), while the reaction between cathode material and electrolyte accelerates the structural degradation of the bulk [9–10]. The effect of lithium residues on the surface of particles such as LiOH and Li₂CO₃ on the impedance increase and rapid capacity decay is not negligible [10–11]. Furthermore, in the nickel-rich layered LiNi_{1 − x−y}Co_xMn_yO₂ system, another approach to increase the reversible capacity is raising the upper cutoff voltage. However, the structural stability, cycle stability and thermal stability all will decrease at the same time [8, 12].

Many efforts have been made to improve the electrochemical performance of Ni-rich cathode materials, such as metal ion doping, surface modification, and fabricating nanostructured materials [6–22]. Surface coating of cathode materials is considered as an effective modification strategy to improve the surface structural stability, avoid direct contact between cathode active materials and electrolyte, reduce the dissolution of transition metals, and hinder the decomposition of electrolyte, thus further optimizing the electrochemical performance and cycling stability of LIBs [6–8, 10–12]. Coating materials have proven to be significantly effective, including non-metallic C [13], metal oxides Al₂O₃[14], ZrO₂[15–17], fluorides AlF₃[18], LaF₃[19], and AlPO₄[20], Li₃PO₄[21], Mn₃(PO₄)₂ [22], etc. TiO₂ is a competitive cathode coating material due to its unique properties, including abundance, structural stability and electrochemical inertness[8, 12, 23–25]. Ran et al. reported that the surface coating of dual-conductive layers was implemented to optimize the electrochemical performance of LiNi_0.6Co_0.2Mn_0.2O₂ (NCM) under high cut-off voltage (4.5 V) by the integrated use of sol-gel method and in-situ chemical polymerization. The Li₃VO₄-PPy coated NCM electrode exhibits excellent cycling stability at 0.5 C under high cut-off voltage (4.5 V), with a retention rate of 93.7% compared to 73.6% for the pristine NCM after 100 cycles [12].

Nickel-rich LiNi_0.6Co_0.2Mn_0.2O₂ cathode material was coated with nano-sized anatase TiO₂ synthesized via hydrolyzation method to improve its electrochemical performance at high cutoff voltage of 4.5 V [8]. The 1.0 wt.% TiO₂-coated LiNi_0.6Co_0.2Mn_0.2O₂ exhibits a capacity retention of 88.7% after 50 cycles at 1 C and a discharge capacity of 135.8 mAh g^− 1 after 10 cycles at 5 C, comparing to those of the pristine LiNi_0.6Co_0.2Mn_0.2O₂ of only 78.1% and 85.4 mAh g^− 1. The improved electrochemical properties were mainly attributed to the suppression of the interface reaction between the cathode and electrolyte and the improvement of structural stability of the material by coating.

In this work, TiO₂ layer was introduced to modify LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cathode materials by sol-gel method. The synthesis process is simple and easy to implement, and a nanoscale more uniform TiO₂ protective layer was constructed on the surface of the material, and its electrochemical performance was significantly improved. The effects of different contents of TiO₂ coating on the structural and electrochemical performances of the LiNi_0.6Co_0.2Mn_0.2O₂ cathode materials in the cutoff voltage of 4.3 are investigated. At higher cutoff voltage of 4.6 V, the electrochemical performance of different TiO₂ coating of LiNi_0.6Co_0.2Mn_0.2O₂ cathodes were also studied comparatively.

2.1. Synthesis of LiNi _0.6 Co _0.2 Mn _0.2 O ₂ and TiO₂ -coated NCM622(TiO₂-NCM)

The pristine LiNi_0.6Co_0.2Mn_0.2O₂ was prepared by a solid state reaction method. First, the Ni_0.6Co_0.2Mn_0.2(OH)₂ precursor (Zhejiang Power New Energy Co., Ltd) was mixed with LiOH⋅H₂O thoroughly at a molar ratio of 1:1.02. Then, the mixture was heated at 480^◦C for 5 h followed by the calcination at 800 ^◦C for 10 h under the oxygen flow. The obtained sample was marked as NCM622.

The preparation process of TiO₂ -coated NCM622 is shown in Fig. 1. 2 g of NCM622 powder was added into 20 mL ethyl alcohol and stirred for another 2 h, then Tetrabutyl titanate (TBOT) (0.2557 g, 0.6393 g and 1.0655 g corresponds to 2.0, 5.0, and 8.0 wt % TiO₂) was added into the mixed solution and stirred for 1 h. 0.4 mL ammonium hydroxide (NH₃⋅H₂O) were slowly added into the solution under a fixed duration and stirred for 1.5 h. Afterwards, the residual powder was collected by centrifugation and washed with deionized water and ethyl alcohol for several times, then dried under vacuum at 100 ^◦C for 10 h. The final product was obtained by annealing the dried powder in a muffle furnace at 500 ^◦C for 4 h. The obtained samples were marked as 2.0 wt %, 5.0 wt %, and 8.0 wt %TiO₂-NCM622, respectively, according to the addition content of TiO₂.

2.2. Characterizations

The crystal structures of NCM622 and TiO₂-coated NCM600 samples were characterized by X-ray powder diffraction (XRD) (Bruker AXS, D8 diffractometer, Gemany) using a Cu-Kα source from 10 to 70°. The morphology and microstructure of the samples were observed by transmission electron microscopy (TEM) (Thermo Scientific Talos F200S G2 200kV), and scanning electron microscopy (SEM) (JEOL JSM-7100F, Japan), X-ray (EDX) detector (Oxford Instruments, INCA). The chemical states of Ni, Co, Mn, O, Ti and C were characterized by X-ray photoelectron spectroscopy (XPS) (VGESCA-LABMK II).

1.3. Electrochemical measurements

Electrochemical performance of the samples (NCM622 and TiO₂ coated NCM622 samples) was evaluated using CR2025 coin-type half-cells. The electrodes were prepared by mixing the NCM622 and TiO₂ coated NCM samples (80 wt.%), carbon black (BP2000) (10 wt.%) and polyvinyldifluoride (PVDF) (10 wt. %) with moderate amount of NMP and pasting onto Al foil. The electrolyte was 1 mol L^− 1 LiPF₆ in a mixture of diethyl carbonate (DEC), ethylidene carbonate (EC) and dimethyl carbonate (DMC) (1:1:1 by volume). The coin-type cells were assembled in an Ar-filled glove box using metal Li foil as counter electrode, diaphragm as the separator. For the charge and discharge test, an automatic battery test system (Neware, China) with the different voltage ranges of 3.0 ~ 4.3 V and 3.0 ~ 4.6 V was used. Electrochemical impendance spectroscopy (EIS) and cyclic voltammetry (CV) measurements of the cells were performed on an electrochemical workstation (CHI 660E, China).

Figure 2 shows the XRD patterns of the synthetic pristine NCM622 and TiO₂ coating of NCM622 samples. For all the prepared anode samples, 10 strong diffraction peaks were observed in the XRD spectra from 10º to 70º, which correspond to the characteristic peaks (003), (101), (006), (102), (104), (105), (107), (108), (110) and (113) of the typical hexagonal crystalline α-NaFeO₂ structure of the R3 space group. No other peaks of impurities was detected, indicating that the addition of TiO₂ does not change the phase structure of NCM622 material. The absence of diffraction peaks of TiO₂ may be due to the samll amount of TiO₂ coating. Sharp and distinct splits between the two sets of split peaks (006)/(102) and (108)/(110) show that the as-prepared samples have a well-developed layered structure. This suggests that the crystal structure of NCM622 is not affected by the TiO₂ coating.

Table 1 shows the computed lattice parameters, as well as the intensity ratio of I₀₀₃/I₁₀₄. Obviously, with the increase of coating content of TiO₂, a and c axes show slightly expansion. The c/a values of all five samples are over 4.9, which indicate that the all obtained NCM622 samples have a layered structure. The larger value of c/a not only represents the better crystallinity of the material, but the 5 wt% TiO₂-NCM622 has the largest c/a value and also has the most excellent electrochemical properties.

In addition, the I₍₀₀₃₎/I₍₁₀₄₎ values of bare MCM622, 2%wt, 5%wt, 8%wt TiO₂-NCM622 are 1.65, 1.81, 1.83, 1.88, respectively, shown in Table 1. It reveals that as the coating amount of TiO₂ increases, the degree of cation mixing in the material increases. Generally, the ratio of I₍₀₀₃₎/I₍₁₀₄₎ indicates the cation mixing of layered structure; when the I₍₀₀₃₎/I₍₁₀₄₎ ratio > 1.2, the materials have a good layered structure with small cation mixing [21, 24].

Table 1

The lattice parameters (a and c) and I₍₀₀₃₎/I₍₁₀₄₎ of the NCM622 and TiO₂-coated NCM622 samples
Sample	Lattice parameters			I₍₀₀₃₎/I₍₁₀₄₎
Sample	a (Å)	c (Å)	c/a	I₍₀₀₃₎/I₍₁₀₄₎
NCM622	2.8619	14.1927	4.9592	1.65
2wt% TiO₂-NCM	2.8642	14.2036	4.9590	1.81
5wt% TiO₂-NCM	2.8726	14.2497	4.9606	1.83
8wt% TiO₂-NCM	2.8769	14.2623	4.9575	1.88

The structural and elemental analysis of the 5wt%TiO₂-coated NCM622 sample was performed by XPS testing. In Fig. 3(a), the XPS full spectrum of the 5 wt% TiO₂-NCM622 sample shows the presence of Ni, Co, Mn, C, O, and Ti elements. As shown in Fig. 3(b), the three peaks at 284.8, 286.4, and 289.3 eV in the C 1s spectrum correspond to C-C, O-C, and O-C = O, respectively, and the XPS spectrum was corrected by the C-C peak (284.8 eV). From the O 1s spectra of Fig. 3(c), it can be seen that there are three distinct peaks located near 529.3, 531.6 and 532.5 eV, which correspond to lattice oxygen, C-O and oxygen in C = O, respectively. Figure 3(d-f) shows the XPS spectra of the elements Ni, Co, and Mn. The peaks located at 855.08 and 872.68 eV correspond to Ni 2p_3/2 and Ni 2p_1/2, respectively, and the peaks located at 861.58 and 879.18 eV are their satellite peaks, respectively. In the XPS spectrum of element Co, the Co 2p_3/2 peak is 780.28 e V and the Co 2p_1/2 peak is 795.18 eV, indicating that the valence state of Co is + 3. The main peak of Mn 2p_3/2 at 642.58 eV and the Mn 2p_1/2 peak observed at 653.98 eV point to the valence state of Mn being + 4. In the spectrum of Ti 2p (Fg.3g) at the binding energies of 458.2, 463.9, and 472 eV correspond to the satellite peaks of Ti 2p_3/2, Ti 2p_1/2, and TiO₂, respectively, suggesting that Ti may exist in the form of TiO₂ in the TiO₂-coated NCM622 sample [26–27].

Figure 4(a-d) shows the SEM images of the four samples, which all display uniform secondary spherical particles with the size of about 6–8 µm, indicating that the TiO₂ coating don’t change the morphology of the samples. Figure 4(e,f) shows the high-resolution TEM of 5 wt% TiO₂-NCM, and more uniform TiO₂ coating layer on the individual particles can be observed. The sol-gel method can form the uniform layer of TiO₂ on the surface of NCM622. The thickness of TiO₂ layer is about 5 nm. This nanoscale uniform coating layer can isolate the direct contact between the electrolyte and the active material, reduce the side reactions, and thus improve the electrochemical stability. Moreover, the coating layer can alleviate the structural collapse of the active material due to the volume change caused by delithiation/lithiation during the charging and discharging process, and improve the stability of the layered structure. The EDS results of the 5 wt% TiO₂-NCM622 indicte that the distribution of nickel, cobalt, manganese, oxygen, and titanium elements on the sample surface, shown in Fig. 4(g).

Figure. 5 shows the cyclic voltammetry (CV) curves of 5 wt% TiO₂-NCM622 samples in the voltage range of 2.5–4.5 V with a scan rate of 0.1 mV/s. The samples with different capping contents have similar CV curves. The oxidation peak appearing near 3.9 V and the reduction peak near 3.6 V correspond to the redox reaction of Ni²⁺/Ni⁴⁺, and the redox peak located in the first-cycle corresponds to the plateau appearing in the first charge/discharge curve. In addition, the oxidation peak moves from the high-voltage position in the first turn to the low-voltage direction in the second and third turns, indicating that the first charging and discharging process is an electrochemical activation process for the material to carry out in order to make the cation arrangement more orderly. Thus is advantageous for the detachment and embedding of lithium ions in the subsequent charging and discharging process, which is manifested by the subsequent decrease in the oxidation peak voltage in the second and third turns [28–30].

The constant current charge-discharge curves, cyclic stability, rate performance of pristine NCM622, 2 wt%, 5 wt% and 8 wt% TiO₂-NCM samples are shown in Fig. 6(a-d). In Fig. 6(a-d), apparently, all samples exhibit a plateau region in the first discharge curve, related to the redox reaction between Ni²⁺/Ni⁴⁺, Co³⁺/Co⁴⁺ brought about by deintercalate and intercalate of Li⁺ ions in the crystal lattice. The first cyclic discharge capacity of the 5 wt% TiO₂-NCM622 at 0.3 C is 183.5 mAh g^-1, which is higher than that of the pristine NCM622 of 179.2 mAh g^-1, and the average Coulombic efficiency (CE) of 5 wt% TiO₂-NCM622 can reach 100%. After 100 cycles, the pristine NCM622 show a discharge capacity of 145 mAh g^-1, whereas 5 wt% TiO₂-NCM622 can maintain a dischaege capacity of 163.9 mAh g^-1. The above results indicate that the 5 wt% TiO₂-NCM622 has excellent reversible specific capacity than the pristine NCM622.

Figure 6e shows the cycling stability of the pristine NCM622, 2 wt%, 5 wt% and 8 wt% TiO₂-NCM samples after 100 cycles at 0.3 C. The cycling stability after 100 cycles at 0.3 C is shown in Table 2, where the 5 wt% TiO₂-NCM622 consistently maintains higher capacity and better cycling stability. For the NCM622 electrode, the reversible specific capacity decreases to 145 mAh g^-1 after 100 cycles, whereas the 5 wt% TiO₂-NCM electrode, still release a reversible specific capacity of 163.9 mAh g^-1 after 100 cycles, with a total capacity retention rate of 89.3%.

The multiplicity performance of the samples is shown in Fig. 6(f). In general, the TiO₂-NCM electrodes exhibit better rate performance, compared with bare NCM622. The 5 wt% TiO₂-NCM622 sample exhibits best multiplicity performance, with a discharge specific capacity of average 70 mAh g^-1 at a rate of 10.0 C, compared with ~ 35 mAh g^-1 for bare NCM. The 8 wt% TiO₂-NCM622 sample exhibits worst rate performance, indicating larger coating content of TiO₂ is dverse to the enhancement of electrochemical performance. The appropriate TiO₂ coating of NCM622 has lowest cation mixing and highly ordered lamellar structure, which is conducive to the dislodgement and embedding of Li-ions, and the diffusion kinetics of Li-ion is faster, thus the sample has best rate performance. The as-synthesized 5 wt% TiO₂-NCM622 exhibits best electrochemical performance compared with other TiO₂-coated NCM622 electrodes, as shown in Table 2.

Table 2

The discharge specific capacity and coulombic efficiency of NCM622 and TiO₂-coated NCM samples at 0.3 C.
Sample	Discharge Specific Capacity (mAh g^− 1)		Columbic Efficiency (%)
Sample	1st	100th	Columbic Efficiency (%)
NCM622	179.2	145	80.9
2 wt% TiO₂-NCM	181.9	151	83.0
5 wt% TiO₂-NCM	183.5	163.9	89.3
8 wt% TiO₂-NCM	178.7	135.3	75.7

To verify the electrochemical performance of the modified material under higher voltage, the cyclic performance of NCM622 and 5 wt% TiO₂ NCM622 electrodes was tested under the cutoff voltage of 4.6 V at a higher rate of 0.5 C, as shown in Fig. 7. The initial discharge capacities of NCM and 5 wt% TiO₂-NCM622 electrodes are ~ 200 and 205 mAh g^-1, respctively. The cycling performance of the 5 wt% TiO₂ NCM622 electrode is improved, compared with bare NCM622. After 150 cycles, the 5 wt% TiO₂-NCM622 electrode shows a specific capacity of 107.3 mAh g^-1, which is higher than that of 80.8 mAh g^-1 of the bare NCM622. Therefore, after TiO₂ coating, the harmful effects of the modified material under higher voltage are also suppressed to a certain extent, similar to the reslts measured at a cut-off voltage of 4.3 V. However, under the higher cutoff voltage, the capacity retention of NCM622 and TiO₂ coating of NCM622 after 150 cycles is unsatisfied, indicating only TiO₂ coating of NCM622 cannot totally suppress the interface reaction between the cathode and electrolyte and reduce the interface resistance[8, 31].

To further investigate the electrochemical kinetics of the samples, the electrochemical impedance spectroscopy (EIS) tests were performed in the range of 0.01 Hz-100 KHz. As shown in Fig. 8(a), the Nyquist plots of pristine NCM622, 2 wt%, 5 wt%, and 8 wt% TiO₂-NCM622 samples all contain two cross-sections, which are the high-frequency region and low-frequency region cross-sections, respectively. The semicircle in the high-frequency region corresponds to the charge transfer resistance (R_st), and the larger the diameter of the semicircle is, the larger the charge transfer resistance is. The specific R_st values are shown in Table 4. It can be found that the 5 wt% TiO₂-NCM622 electrode has the smallest charge transfer resistance. The straight line in the low-frequency region corresponds to the Warburg resistance (A_w) of the diffusion of Li-ion inside the electrode, and the larger the slope is, the larger is the Warburg resistance, as in Fig. 8(b). The Warburg coefficients of the three electrodes, NCM622, 2 wt% TiO₂-NCM, 5 wt% TiO₂-NCM, and 8 wt% TiO₂-NCM, are 38.29, 28.71, 23.93, and 52.65 Ω s^-1/2, respectively, by fitting, which proves that the 5 wt% TiO₂-NCM622 has a faster electrochemical kinetics.

Table 4

The Charge transfer resistance (R_st) of NCM and TiO₂-coated NCM samples
Sample	NCM622	2 wt% TiO₂-NCM	5 wt% TiO₂-NCM	8 wt% TiO₂-NCM
EIS(Ω)	191	142	113	258

Table 5 shows a comparison of the partial electrochemical performance of TiO₂-coated NCM with the previously reported electrochemical performance of partial coating NCM cathodes in LIBs.

Table 5

Comparison of electrochemical performances of part of coated LiNi_0.6Co_0.2Mn_0.2O₂ (NCM) with previously work reported for LIBs.
Samples	Rate (C) / Cutoff voltage (V)	Cycles	Capacity (mAh g^–1) / Retention (%)
ZrO₂ modified NCM [17]	0.1 / 2.8–4.5	100	154.8 / 82.5
TiO₂-modified NCM [23]	1.0 / 2.5–4.3	100	163.6 / 85.9
Li₂SnO₃ coating NCM [26]	1.0 / 3.8–4.5	100	136.2 / 85.94
AlPO₄ coating NCM [20]	1.0 / 2.8–4.3	50	135.5 / 86.2
Mn₃(PO₄)₂ coating NCM [22]	0.5 / 3-4.3	50	149 / 93.3
5wt% TiO₂-NCM (This work)	0.3 / 3-4.3	100	163.8 / 89.3
5wt% TiO₂-NCM (This work)	0.5 / 3-4.6	150	107.3/53.5

In summary, TiO₂-coated NCM622 material was successfully synthesized by sol-gel method, and a uniform nanolayer-scale TiO₂ coating layer was formed on the surface of TiO₂-NCM material. When the TiO₂-NCM material was used as the positive electrode of LIB, it showed better electrochemical performance, and the 5 wt% TiO₂-NCM material had a discharge capacity of 163.9 mAh g^-1, and at a large multiplicity condition of 10 C, the discharge capacity still has about 50 mAh g^-1. The 5 wt% TiO₂-NCM material exhibits satisfactory electrochemical performance, which is mainly attributed to the homogeneous cladding layer attenuating the side reactions between the material and the electrolyte, as well as providing a more stable structure. This study provides an effective method for the synthesis and modification of high-performance NCM622 for lithium ions battery applications.

CRediT authorship contribution statement

Lin Li: Visualization, Methodology, Investigation, Formal analysis, Data curation. Zhongyu Li: Visualization, Methodology, Investigation, Formal analysis, Data curation. Zhifan Kuang: Investigation, Data curation. Minjian Yang: Investigation, Data curation. Jianwen Liu: Writing – review & editing, Supervision, Resources, Funding acquisition. Shiquan Wang: Writing – review & editing, Supervision, Resources, Funding acquisition. Hongying Liu: Investigation, Data curation. Lin Li: Writing – review & editing, Supervision, Resources, Funding acquisition.

Acknowledgements

This work was financially supported by the Project of the Three Gorges Laboratory of Hubei Province (No. SK211005), Key Laboratory for Research and Development of new lithium-ion battery materials (2023-028), the Joint Foundation Project of Bijie City Science and Technology Burean and Guizhou University of Engineering Science (BiKeLianhe[2023]39), and Joint Fund of Bijie City and Guizhou University of Engineering Science (BiKeLianhe [2023] 12^th)

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Effect of TiO₂ coating on structure and electrochemical performance of LiNi_0.6Co_0.2Mn_0.2O₂ cathode material for lithium ion batteries

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Introduction

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2.2. Characterizations

1.3. Electrochemical measurements

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