Electrochemical Performance Of LiNi0 Research Articles

Boosting Electrochemical Performances of High-Voltage NCA/LTO Cells by Cathode Electrolyte Interface Nano Film Formation in Ionic Liquid Electrolyte

LiTFSI/EMITFSI ionic liquid was applied in this study as an electrolyte to enhance electrochemical performances of LiNi0.8 Co0.15 Al0.05 O2 /Li4 Ti5 O12 (NCA/LTO) batteries at a high charging cutoff voltage of 3.2 V. Li-EMITFSI electrolyte generated extremely stable and uniform cathode electrolyte interface (CEI) nano film on the cathode surface. This CEI film not only inhibited the continuous decomposition of electrolyte, but also stabilized the high operating voltage of NCA/LTO batteries, resulting in enhanced discharge gravimetric specific capacity (Cg) and cyclic stability of NCA/LTO batteries. With Li-EMITFSI electrolyte, the NCA/LTO batteries achieved higher C g of 172 mAhg –1 at 0.1 C and good capacity retention of 75% over 50 cycles at 1.4 ~ 3.2 V, compared to traditional commercial electrolytes.

Influence of the Li/TM Ratio on Electrochemical Properties of LiNi0.9Co0.1O2 Cathodes

The layered Nickel-rich LiNixMyO2 (Ni ≥60%) cathodes have attracted much attention owing to their high energy density, promising cycle property and low cost. Nevertheless, their electrochemical performances greatly depend on the synthesis conditions, especially for the ratio of lithium to transition metal (Li / TM). Herein, we have systematically investigated the influence of Li/TM on structure and electrochemical performance of LiNi0.9Co0.1O2 cathodes. The optimized LiNi0.9Co0.1O2 (Li/TM is 1.02) exhibits highest initial capacity of 189.8mAh g−1 at 1 C and much better capacity retention of 82.19% after 100 cycles between 2.8 and 4.35 V at 1 C.

Influence of Ti doping on microstructure and electrochemical performance of LiNi0.5Mn1.5O4 cathode material for lithium-ion batteries

LiNi0.5Mn1.5O4 cathode material has been synthesized by a combined coprecipitation-hydrothermal method followed by high-temperature calcination. Ti doping was achieved via acetic acid glacial assisted sol-gel method by using titanium(IV) butoxide as Ti source. The effects of different Ti doping contents on the structure, morphology and electrochemical properties of LiNi0.5Mn1.5O4 materials were systematically investigated. The as-synthesized samples were characterized by XRD, FT-IR, SEM, TEM, XPS, EIS and constant-current charge/discharge test. It is found that although Ti doping can effectively inhibit the formation of LixNi1-xO impurity phase, excessive Ti doping results in the appearance of Li2TiO3 secondary phase. SEM observation shows that Ti doping can improve the crystallinity of particles, and particle size shows a gradual increasing trend with Ti doping content. LiNi0.5Mn1.5O4 material doped with 3% Ti shows high phase purity and crystallinity, appropriate Mn3+ content and particle size with uniform distribution, thereby leading to its optimal electrochemical performance. Its discharge capacity at 10 C rate can reach 127.3 mA h g−1, and capacity retention rate can reach 91.7 % after 200 cycles at 1C and 25 °C. Post-mortem analysis shows that appropriate Ti doping can efficiently ameliorate electrolyte decomposition and other side reactions, thus leading to the formation of thinner SEI/CEI layer on electrode surface, and then better cycling performance achieved.

Effects of Si doping on structural and electrochemical performance of LiNi0.5Mn1.5O4 cathode materials for lithium-ion batteries

LiNi0.5Mn1.5O4 spinels were prepared by coprecipitation-hydrothermal method followed by high-temperature calcination. Si doping was achieved by acetic acid glacial-assisted sol-gel method using TEOS as Si source. The effect of Si doping contents on the structure, morphology and electrochemical performance of LiNi0.5Mn1.5O4 material was investigated. Si doping can inhibit the formation of LixNi1-xO impurity, but excessive Si doping results in the appearance of Li2SiO3 secondary phase. Si doping can reduce particle size and improve distribution. Electrochemical tests show that Si doping has a positive impact on rate and cycling performances, due to the increased structural stability resulting from stronger SiO bond, and the enhanced Li+ ion diffusion coefficient. Post-mortem analysis shows that Si doping can mitigate the transition metal dissolution and side reactions, thus leading to the enhanced electrochemical performance of Si-doped samples. Among them, LiNi0.5Mn1.5O4 with 6% Si doping exhibits the optimal electrochemical performance.

Effects of the Mixing Sequence on Making Lithium Ion Battery Electrodes

Slurry making is a critical step that can irrevocably affect the subsequent steps in battery manufacturing. Many experimental parameters, including the mixing sequence, must be considered in making the slurry. In this work, we investigated the effects of the two main industry-used mixing sequences on the rheological behavior of the slurry, and the relation of the slurry rheology to structural, mechanical, and electrochemical performance of LiNi0.33Mn0.33Co0.33O2 (NMC) electrodes. We show that: (1) mixing carbon black (CB) with polyvinylidene fluoride (PVDF) solution before adding NMC can facilitate the formation of a gel-like slurry; (2) porous clusters of CB/PVDF can form around NMC after drying the gel-like slurry, providing a high C-rate capability; (3) dry powder mixing of CB and NMC can facilitate the binding of the CB to the NMC surfaces, reducing the amount of CB in the PVDF and resulting in a liquid-like slurry; (4) after drying of the liquid-like slurry, a dense CB/PVDF layer can form on the NMC surfaces; and (5) this dense layer can provide high binding strength but may block ionic transport and weaken the electronic connection, reducing the C-rate capability. Thus, it is critically important to understand the effects of mixing sequence in electrode manufacturing.

Effects of Graphite Heat-Treatment Temperature on Single-Crystal Li[Ni5Mn3Co2]O2/Graphite Pouch Cells

In this work, the effect of the heat-treatment temperature of synthetic (artificial) graphite on the electrochemical performance of LiNi0.5Mn0.3Co0.2O2/graphite pouch cells was explored and compared with cells utilizing commercial-grade artificial and natural graphite materials. Two optimized electrolyte additive blends, 2% VC + 1% DTD and 1% LiPO2F2, were used in the cells tested. Physical properties of the different graphite electrodes, such as morphology, pore-size, crystallinity and thermal stability were investigated. Then, cells with each graphite material were tested with a variety of electrochemical techniques: ultra-high precision coulometry, long-term cycling, high-rate cycling, isothermal microcalorimetry, operando pressure tests and open circuit storage tests. Marginal benefits were found in electrochemical tests for cells with graphite materials that had been heat-treated to lower temperatures. However, in all tests, cells with synthetic graphite had superior performance compared to natural graphite.

Synthesis and electrochemical performances of LiNi0.5Mn1.5O4 spinels with different surface orientations for lithium-ion batteries

LiNi0.5Mn1.5O4 materials with three different particle shapes, including octahedron composed of {111} surface, truncated octahedron with {111} and {100} surfaces, and chamfered polyhedron with {111}, {100}, and {110} surfaces, have been synthesized via a combined coprecipitation-hydrothermal method followed by three different calcination processes. The materials were characterized by XRD, FT-IR, SEM, EIS, XPS, and galvanostatic charge/discharge tests. All samples have a main disordered structure and similar primary particle size. Electrochemical results show the rate capability degrades in the order of chamfered polyhedron > truncated octahedron > octahedron, while the cycling stability deteriorates in the order of truncated octahedron > octahedron > chamfered polyhedron. It can be concluded that the particle shape, more specifically, surface orientations, exerts great influence on the electrochemical performance of LiNi0.5Mn1.5O4 material. Therefore, appropriate tailoring of surface orientations can simultaneously satisfy power capability and long cycle life. The particle shape design is of significance to LiNi0.5Mn1.5O4 material.

Impact of evolution of cathode electrolyte interface of Li(Ni0.8Co0.1Mn0.1)O2 on electrochemical performance during high voltage cycling process

Abstract In this work, the electrochemical performance of LiNi0.8Co0.1Mn0.1O2 (NCM811) has been investigated after cycling with various upper cutoff voltages. Noteworthily, electrochemical impedance of NCM811 declined with the increasing cycle number to high voltages. It was found that the decline of charge transfer impedance could be related to the structural and compositional change of cathode electrolyte interphase (CEI) of NCM811 when charging to high voltages, based on the characterization of electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The corresponding mechanism has also been proposed in this study. Specifically, due to the increasing roughness of cathode surface, the bottom of CEI film and cubic phase on cathode surface form a transition region mainly at high voltages, leading to the nonobvious boundary. This newly formed transition region at high voltages could promote the Li ion diffusion from electrolyte to cathode, then reducing charge transfer impedance. Additionally, the decrease of LiF on the surface of the cathode could also make a contribution to lower the interface impedance. This study delivers a different evolution of CEI on NCM811, and the impact of CEI evolution on electrochemical performance when charging to a high voltage.

Effect of Mg2+/F− co-doping on electrochemical performance of LiNi0.5Mn1.5O4 for 5 V lithium-ion batteries

Mg2+/F− co-doped LiNi0.5Mn1.5O4 cathode material was synthesized by a facile one-step solid-state process. The effect of Mg2+/F− co-doping on grain morphology, phase structure, and electrochemical properties was studied by a series of characterizations. Scanning-electron-microscopy images show that Mg2+/F− co-doped LiNi0.5Mn1.5O4 (denoted LNMO-MF) particles grow larger than pure LiNi0.5Mn1.5O4 particles. X-ray diffraction, Raman spectra, Fourier transformation infrared spectroscopy, X-ray photoelectron spectroscopy, and cyclic-voltammetry tests indicate that all samples mainly display a Fd-3m space group and more Mn3+ ions in the LNMO-MF sample after Mg2+/F− co-doping, which is conducive to increasing the cationic disorder degree and enhancing the electronic conductivity of electrode material. Results show that the LNMO-MF cathode material delivers an excellent rate performance with discharge capacities of 142, 144, 140 136, 132, 124, 115, and 100 mAh g−1 at 0.2, 0.5, 1, 2, 3, 5, 7, and 10C (1C = 140 mAh g−1), respectively. Remarkably, LNMO-MF also shows cycling stability with a capacity retention of 86.2% at 5C after 400 cycles, which is much higher than that of pure LiNi0.5Mn1.5O4 (67.7%). The improvement of LNMO-MF's electrochemical properties could be ascribed to the Mg2+/F− co-doping, delivering a more stable structure, better crystallinity, the highest Li+ diffusion coefficient, and the lowest charge-transfer resistance.

Improving the cycling performance of LiNi0.8Co0.15Al0.05O2 cathode materials via zirconium and fluorine co-substitution

High-nickel layered transition-metal oxides with large reversible capacity typically suffer from crystal instability and fast capacity decay during cycling. Herein, we report a co-substitution strategy using traditional solid state sintering technology to incorporate zirconium (Zr) and fluorine (F) into LiNi0.8Co0.15Al0.05O2 cathode materials. The effects of the substitution on the crystal structure, morphology and electrochemical performance of LiNi0.8Co0.15Al0.05O2 were investigated by the combinations of XRD, SEM, EDS, XPS, CV, galvanostatic charge-discharge tests and EIS. The results show that F substitution stabilizes the crystal structure. However, it increases the degree of the cation mixing and degrades the reversible capacity. Zr substitution effectively stabilizes the crystal structure and reduces the cation mixing due to the strong bond dissociation energy of Zr–O. Our study suggests that the Zr and F co-substitution facilitates the transport of lithium ions, mitigates the electrochemical polarization and significantly enhances the structural stability. The Zr and F co-doped sample shows capacity retention of 90.5% after 200 cycles at 1 C, while that of bare sample remained only 75.8%. This work sheds lights on understanding the effects of multi-ion substitution on improving electrochemical performance of high-nickel layered cathodes.

Synthesis and Electrochemical Performances of the High Nickel Content Layer-Structured Cathode Materials for High-Energy Libs

Among the various cathode candidate, layer structured Li(Ni,Co,Mn)O2 (NCM) has been regarded as the most attractive alternative to LIBs owing to relatively modest volume change (LiCoO2), high specific capacity (LiNiO2) and good thermal stability (LiMn2O4). Although Li(Ni1/3Co1/3Mn1/3)O2 has been successfully commercialized as a battery cathode, researches on Ni-rich NCM (LiNixCoyMn1−x−yO2, x > 0.5) have been spotlighted due to its superior capacity (> 200 mAh/g, at 4.6 V vs. Li/Li+) [10]. Therefore, the future of NCM for high energy LIBs strongly depends on Ni-rich NCM materials. It is reported that crystallinity and morphology, influenced by the sintering temperatures, all play important roles in the electrochemical performances. In this paper, we report the synthesis of LiNi0.91Co0.06Mn0.03O2 cathode materials with different sintering temperatures. Also the relationship between the sintering temperatures and the electrochemical performances is investigated. The sintering temperatures affect a crystallinity and morphology, which play an important role in electrochemical performances of LiNi0.91Co0.06Mn0.03O2. The electrochemical performances have improved with increasing sintering temperatures. The LiNi0.91Co0.06Mn0.03O2 sintered at 720 oC shows remarkably excellent performance: initial discharge capacity: 100 mAh/g, cycle performance: 98 % retention after 100 cycles (at 0.5 C) and rate capability: 88 % (at 2 C). These results indicate that LiNi0.91Co0.06Mn0.03O2 can be regarded as a next generation cathode for high-performance lithium ion batteries.

Synergistic effect of surface plane and particle sizes on the electrochemical performance of LiNi0.5Mn1.5O4 cathode material via a facile calcination process

A series of LiNi0.5Mn1.5O4 cathode samples with different morphologies was synthesized via a template method and facile post-calcination process. Rod-like and truncated octahedral particles with {111} surface are obtained through increasing the calcination temperature. The exposed surface of as-prepared materials is mainly detected by SEM and TEM images. Detailed characterization of electrochemical performance of samples reflects that the T-775 cathode sample displays superior rate capability, and the discharge capacity reaches 108.2 mAh g−1 at 100C. The energy density of full cells, T-775 sample as the cathode material and commercial graphite as the anode material, retain 534.9 Wh kg−1 after 100 cycles. These improvements might be due to the synergistic effect of the {111} surface and smaller particle sizes, which improves interfacial stability and reduces the diffusion distance of Li+ during the interaction/deinteraction process.

Preparation and electrochemical performances of Ni-rich LiNi0.91Co0.06Mn0.03O2 cathode for high-energy LIBs

Abstract One important challenge of lithium ion batteries is to improve the energy density while maintaining long-term cyclability. The energy density is strongly dependent on the Ni content in LiNi1-x-yCoxMnyO2. Herein, Ni-rich LiNi0.91Co0.06Mn0.03O2 has been synthesized as a high energy cathode material by co-precipitation method and the electrochemical performance of the LiNi0.91Co0.06Mn0.03O2 has been investigated. The granule morphology LiNi0.91Co0.06Mn0.03O2 with high crystallinity is obtained and which delivers a discharge capacity of 208.3 mA h g−1 with cyclability of 61.9%, after 100 cycles and rate performance of 85.6%, at 2 C. These findings indicate that LiNi0.91Co0.06Mn0.03O2 is one of the promising candidate cathode for high-energy lithium ion batteries.

Effects of lithium excess and SnO2 surface coating on the electrochemical performance of LiNi0.8Co0.15Al0.05O2 cathode material for Li-ion batteries

Four LiNi0.8Co0.15Al0.05-based Li-ion-battery cathode materials, i.e., the pristine LiNi0.8Co0.15Al0.05, Li-excess Li1+xNi0.8Co0.15Al0.05, SnO2-coated LiNi0.8Co0.15Al0.05 and SnO2-coated Li-excess Li1+xNi0.8Co0.15Al0.05 are prepared via a facile oxalate coprecipitation route, and are studied with respect to the effects of Li excess and SnO2 coating on the structure and electrochemical properties. X-ray diffraction and X-ray photoelectric spectroscopy demonstrate that a small amount of Li+ and/or Sn2+ ions are incorporated into the transition-metal slabs of the modified materials, and hence reduce the cationic disorder of Li+/Ni2+. High-resolution transmission electron microscopy and scanning electron microscopy confirm the formation of a SnO2 surface layer that prevents the growth and aggregation of the primary particles during high-temperature solid reaction, and therefore results in formation of the SnO2-coated materials with nano/submicron sphere-like morphology. Lithium excess and SnO2 coating enhance the electrochemical performance. The SnO2-coated Li-excess Li1+xNi0.8Co0.15Al0.05 exhibits not only higher specific capacity and better rate capability but also excellent cycling stability. After 400 cycles at 1C rate, the capacity is decreased from 123.7 to 86.7 mAh g−1, giving capacity retention of 70.1%. Li excess is believed to decrease the cationic mixing and SnO2 modification is deemed to restrict the undesirable side reaction between the active material and electrolyte.

Effect of metal ion concentration in precursor solution on structure and electrochemical performance of LiNi0.6Co0.2Mn0.2O2

LiNi0.6Mn0.2Co0.2O2 (622NCM) cathode materials are synthesized by a carbonate co-precipitation process. We decomposed Co and Mn carbonates to form porous CoMnO3 precursors, which were impregnated with Ni and Li salts to form final materials. To provide better hosts for the Ni and Li salts, we design the co-precipitation solutions with different total metal ion concentrations to achieve precursors with stable structures and appropriate porosity. We obtained 622NCM with hierarchical and porous properties, which shortened the lithium ion transmission distance and improved the electrolyte infiltration rate and rate capability. Furthermore, our 622NCM cathode materials showed no loss of thermodynamic or electrochemical stability during cycling. The most suitable concentration was determined to be 0.03 mol L−1 and the as-prepared 622NCM (0.03–622NCM) cathode material exhibited good cycle reversibility, a high capacity, and good rate capability, delivering a discharge capacity of 152 mA h g−1 at 0.2 C. A capacity of more than 100 mA h g−1 was achieved at a high rate of 5 C. This study provides guidance for preparing nickel-rich ternary cathode materials for high-performance lithium-ion batteries.

Structure and electrochemical performance of LiNi0.6Co0.1Mn0.2Fe0.1O2 tetrad cathode material for Li-battery

In the study, the (Ni0.6Co0.1Mn0.2Fe0.1)C2O4 precursor was synthesized according to the oxalate co-precipitation method under different pH values and then layered Ni-rich LiNi0.6Co0.1Mn0.2Fe0.1O2 (6121) materials were prepared by calcinating the mixture of oxalate precursor and LiOH·H2O in an oxygen atmosphere. The crystal structure, morphology, chemical compositions, and electrochemical behaviors of the tetrad cathode materials were explored respectively by XRD, SEM, HRTEM, EDS, and electrochemical charge–discharge tests. The XRD results revealed that the ratios of c/a and I(003)/I(104) respectively increased from 4.989 to 1.47 to 5.000 and 1.61 after Fe substituted Co in LiNi0.6Co0.2Mn0.2O2 (622). SEM images showed that spherical particles were more uniform and that the particle diameter decreased from 15 µm to 10 µm after the introduction of Fe. The results of charge/discharge tests indicated that the LiNi0.6Co0.1Mn0.2Fe0.1O2 sample had the lower polarization (10% at 0.1 C), the higher cycling retention (86% after 100 cycles at 1 C), and the enhanced rate performance. The LiNi0.6Co0.1Mn0.2Fe0.1O2 sample showed the better reversibility, smaller impedance parameters and a larger Li+ diffusion coefficient in CV and EIS analyses. This study provides a promising tetrad cathode material with the better crystal structure, higher columbic efficiency and better cycle performance. The new tetrad cathode material is expected to become part and parcel of cathode materials.

Enhanced electrochemical performance of Li3PO4 modified Li[Ni0.8Co0.1Mn0.1]O2 cathode material via lithium-reactive coating

Residue lithium is recognized as one of the critical factors affecting the electrochemical performances of LiNiO2-based cathode materials. In this paper, Li3PO4-modified LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material is successfully synthesized via a wet coating followed by a heat treatment. As a consequence, the contents of surface residual lithium are significantly reduced as confirmed by neutralization titration, which can be ascribed to the formation of a Li3PO4 coating layer by the reaction between surface residual lithium and (NH4)2HPO4. The effects of Li3PO4 coating on the surface states, crystal structure and electrochemical performances of LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material are studied in detail. After 100 cycles, the capacity retention of Li3PO4-coated NCM811 is 92.6% at 25 °C at 1C, whereas the bare NCM811 is only 86.1%. Besides, the Li3PO4-coated NCM811 delivers a better rate property of 159.4 mAh·g−1 at 8C compared with 144.4 mAh·g−1 for NCM811. The prominent improvements in electrochemical performances are attribute to the fact that the formation of Li3PO4 coating layers help to remove the surface residual lithium, facilitate lithium ion diffusion, lower the level of HF and H2O in the electrolyte and suppress the deleterious side reactions between the electrolyte and active materials.

Ti3C2(OH)2 coated Li(Ni0.6Co0.2Mn0.2)O2 cathode material with enhanced electrochemical properties for lithium ion battery

Ti3C2(OH)2 coated nickel-rich LiNi0.6Co0.2Mn0.2O2 cathode material is prepared with wet coating process. The effects of the Ti3C2(OH)2 concentration on the structure and electrochemical performance of LiNi0.6Co0.2Mn0.2O2cathode materials are investigated. The microanalyses show that Ti3C2(OH)2 is successfully coated on the surface of LiNi0.6Co0.2Mn0.2O2 cathode material. All cathode materials display the excellent hexagonal ordering and the low ratio of I(006+102)/I(101). Furthermore, the Ti3C2(OH)2 coated cathode materials presents excellent cycling capability and rate capability. Among them, the 3.0 wt.% Ti3C2(OH)2 coated LiNi0.6Co0.2Mn0.2O2 displays the highest discharge capacity of 124.5 mAh/g with the capacity retention of 86.4% after 200 cycles at 0.5 C, and the best rate performance at high current density. So Ti3C2(OH)2 coating is good promising material for LiNi0.6Co0.2Mn0.2O2 to improve the long-life and rate capability.

Effects of polyvinyl alcohol on the electrochemical performance of LiNi0.8Co0.15Al0.05O2 cathode material

In view of the close relationship between the morphology of LiNi0.8Co0.15Al0.05O2 (NCA) and its electrochemical performance, polyvinyl alcohol (PVA) was added to control the NCA morphology. And thus a new NCA cathode material modified by PVA (NCA-PVA) was prepared. The morphology and structure of the obtained samples were characterized by X-ray diffraction, scanning electron microscopy, and laser diffraction. The electrochemical performance was characterized with electrochemical workstation and cell tester by assembling into CR2032 coin-type half-cell. The results show that the obtained NCA-PVA has a better layer structure and smaller cation mixing degree, smaller particle size, and more uniform particle size distribution than the pristine NCA without adding PVA. The electrochemical performance is also improved: the initial discharge capacity increases from 143.36 to 184.84 mAh g−1. And the charge-discharge efficiency increases from 78.25 to 86.42%. The specific discharge capacities of NCA-PVA are all higher than that of the NCA (about 50 mAh g−1) at all testing rates (0.1, 0.2, 0.5, 1.0, 2.0, and 5.0 C).

Resynthesis and electrochemical performance of LiNi0.5Co0.2Mn0.3O2 from spent cathode material of lithium-ion batteries

LiNi0.5Co0.2Mn0.3O2 (LNCM) was resynthesized by a novel metallurgical approach coupled with solid-state sintering using cathode materials from spent lithium-ion batteries (LIBs) as starting materials. A combination of reduction roasting, two-step leaching, co-precipitation, and solid-state reaction was applied to recover valuable metals and regenerate cathode materials. The prepared LNCM was characterized by a series of physical and electrochemical measurements for comparison with commercial LNCM. X-ray diffraction and scanning electron microscopy results indicate that the resynthesized LNCM exhibits good layered structure and a sphere of approximately 6 μm. The electrochemical tests indicate that the resynthesized LNCM has an initial discharge capacity of 172.9 mA h g-1 (0.2 C) between 2.5 and 4.3 V; the discharge capacity is 160.9 mA h g-1 (0.2 C) after 50 cycles, in which the capacity retention is 93.8%. Cyclic voltammograms and electrochemical impedance spectra detected that resynthesized LNCM has good structural reversibility and conductivity, similar to commercial LNCM. This method is feasible for regenerating the spent cathode material of LIBs, which can contribute to both resource recycling and environmental protection.