Surface Of LiNi0 Research Articles

Coupling-Agent-Coordinated Uniform Polymer Coating on LiNi0.6Co0.2Mn0.2O2 for Improved Electrochemical Performance at Elevated Temperatures.

The high-voltage Ni-rich LiNixCoyMnzO2 cathode materials attract attention due to their high capacity and relatively low cost. However, the undesired instability originating from side reactions with liquid electrolytes at elevated temperatures still hinders their practical application. This research aims to build a stable interface between cathode and electrolyte. We use the coupling agent KH570 to induce vinyl ethylene carbonate (VEC) monomers to in situ polymerize on the surface of LiNi0.6Co0.2Mn0.2O2 (NCM622) to form a uniform, ultrathin (∼12 nm), and highly ion-conductive poly(vinyl ethylene carbonate) (PVEC) solid polymer electrolyte layer. The modified cathode material exhibits significant improvement in rate performance and cycling stability up to 4.5 V at elevated temperatures. Scanning electron microscopy and X-ray diffraction techniques prove that the flexible polymer coating layer effectively suppresses the mechanical degradation and crystal structure changes during cycling.

Efficient preservation of surface state of LiNi0·82Co0·15Al0·03O2 through assembly of hydride terminated polydimethylsiloxane

Surface engineering of nickel-rich materials can efficiently prevent the materials from adsorbing water and CO2 in the atmosphere to restrain the formation of the insulating Li2CO3 on the surface of the materials. Herein, we report a facile approach to preserve the surface state of LiNi0·82Co0·15Al0·03O2 via surface self-assembly of hydride terminated polydimethylsiloxane. The hydride terminated polydimethylsiloxane can be tightly linked to the hydroxyl groups on the surface of LiNi0·82Co0·15Al0·03O2 through hydrogen bonding likely as a monolayer, endowing the surface of the material with strong hydrophobicity. Consequently, the LiNi0·82Co0·15Al0·03O2 material modified with the siloxane polymer after stored for 14 days exhibits electrochemical performance similar to that of the fresh pristine counterpart, whereas the stored pristine sample shows severely deteriorated performance due to the formation of the thick Li2CO3 layer insulating to lithium ion transportation at the electrode/electrolyte interface. Furthermore, the similarity in the initial discharge capacity, cyclability and rate capability of the fresh pristine and siloxane polymer-modified samples demonstrates that differing from coating of most inorganic materials, the modified layer is favorable to the lithium ion transportation, probably due to rich oxygens in the backbone of the siloxane polymer.

Enhancing the Stability of LiNi0.5Mn1.5O4 by Coating with LiNbO3 Solid-State Electrolyte: Novel Chemically Activated Coating Process versus Sol-Gel Method.

LiNbO3-coated LiNi0.5Mn1.5O4 spinel was fabricated by two methods: using hydrogen-peroxide as activating agent and sol-gel method. The structure of the obtained cathode materials was investigated using a scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and the electrochemical properties of the prepared cathodes were probed by charge-discharge studies. The morphology of the coating material on the surface and the degree of coverage of the coated particles were investigated by SEM, which showed that the surface of LiNi0.5Mn1.5O4 particles is uniformly encapsulated by lithium innovate coating. The influence of the LiNbO3 coating layer on the spinel’s properties was explored, including its effect on the crystal structure and electrochemical performance. XRD studies of the obtained coated active materials revealed very small expansion or contraction of the unit cell. From the capacity retention tests a significant improvement of the electrochemical properties resulted when a novel chemically activated coating process was used. Poorer results, however, were obtained using the sol-gel method. The results also revealed that the coated materials by the new method exhibit enhanced reversibility and stability compared to the pristine and reference ones. It was shown that the morphology of the coating material and possible improvement of communication between the substrates play an important role.

Enhanced electrochemical performance of Ni-rich cathode material by N-doped LiAlO2 surface modification for lithium-ion batteries

LiNi0.6Co0.2Mn0.2O2 (NCM) cathodes are regarded as prospective cathodes for high-performance Lithium ion batteries due to its low costs and high energy density. Nevertheless, poor electrochemical performance severely hinders its further commercial applications. In this study, an effective surface modification strategy to fabricate N-doped LiAlO2 was coated on the surface of LiNi0.6Co0.2Mn0.2O2, and electrochemical performance are greatly enhanced. The nitrogen (N)-doped LiAlO2 (LAO) coated LiNi0.6Co0.2Mn0.2O2 not only exhibit best cycling performance with capacity retention of 87 % after 450 cycles at 1 C (210 mA g−1) under voltage range of 2.7-4.5 V, but also approaches 167 and 154 mAh g−1 at 5 C and 10 C, respectively. The N-doped LiAlO2 surface modified LiNi0.6Co0.2Mn0.2O2 not only suppresses the occurrence of surface side reaction, structural degradation and intergranular cracks, but also remove residual lithium from the LiNi0.6Co0.2Mn0.2O2 surface. Most importantly, in constructed this N-doped LiAlO2 layer, the LiAlO2 with the similar layered structure as LiNi0.6Co0.2Mn0.2O2 can tightly immobilize on the LiNi0.6Co0.2Mn0.2O2 surface, and the N-doping could induce the formation of oxygen vacancies and Al-N bond on surface of the LiAlO2 as well as enlarge interslab distance for the migrating Li+ in the LiAlO2 lattices. These finding not only promoted the commercial application of Ni-rich material, but also provided a new idea for other layered structure cathode.

Suppressed Microcracking and F Penetration of Ni-Rich Layered Cathode via the Combined Effects of Titanium Dioxide Doping and Coating

To understand the effect of heat treatment of TiO2 modification for Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode, the TiO2 coating layer is formed on the surface of LiNi0.8Co0.1Mn0.1O2 cathode by heat treat...

Effects of aluminum substitution in nickel-rich layered LiNixAl1−xO2 (x = 0.92, 0.95) positive electrode materials for Li-ion batteries on high-rate cycle performance

Nano-scale Al-rich layers on the surface of LiNi0.92Al0.08O2 and substituted-Al in the crystal suppress both the surface degradation and bulk degradation, resulting in the excellent cycling performance Ni-rich electrode material.

Meticulous guard: The role of Al/F doping in improving the electrochemical performance of high-voltage spinel cathode

Spinel LiNi0.5Mn1.5O4, which is considered as one of the most attractive candidates for high energy density battery due to its high voltage platform over 4.7 V, suffers from the side reactions with electrolyte, strong oxidability of Ni4+ and therefore the complicated and frangible Solid Electrolyte Interfaces (SEI) layer that hinders the practical application of LiNi0.5Mn1.5O4. In this work, traditional co-precipitation method is applied and improved by anion and cation doping method to construct superior interface on the surface of LiNi0.5Mn1.5O4 to suppress side reactions especially at high temperature. Detailed properties including structure, morphology and electrochemical performance of pristine sample, single-doped and co-doped samples are probed. Physical characterizations reveal that the co-doped sample with regular octahedron has a moderate grain size and specific surface area between Al and F single doping, and holds the advantages of rate performance and capacity retention causing by Al doping and better stability under high temperature constructing by F. It exhibits the best capacity retention of 92% after 200 cycles under 55 °C, which is higher than that of the pristine sample (87%). Analysis of the electrode after cycling shows that doping reduces the thickness of the electrode interface film and the content of inorganic substances such as LiF to improve the interface characteristics and the high temperature cycling performance. This work has certain significance for the commercial application of LiNi0.5Mn1.5O4.

Dynamic Evolution of a Cathode Interphase Layer at the Surface of LiNi0.5Co0.2Mn0.3O2 in Quasi-Solid-State Lithium Batteries.

Intensive understanding of the surface mechanism of cathode materials, such as structural evolution and chemical and mechanical stability upon charging/discharging, is crucial to design advanced solid-state lithium batteries (SSLBs) of tomorrow. Here, via in situ atomic force microscopy monitoring, we explore the dynamic evolution process at the surface of LiNi0.5Co0.2Mn0.3O2 cathode particles inside a working SSLB. The dynamic formation process of the cathode interphase layer, with an inorganic-organic hybrid structure, was real-time imaged, as well as the evolution of its mechanical property by in situ scanning of the Derjaguin-Muller-Toporov modulus. Moreover, different components of the cathode interphase layer, such as LiF, Li2CO3, and specific organic species, were identified in detailat different stages of cycling, which can be directly correlated with the impedance buildup of the battery. In addition, the transition metal migration and the formation of new phases can further exacerbate the degradation of the SSLB. A relatively stable cathode interphase is key to improving the performance of SSLBs. Our findings provide deep insights into the dynamic evolution of surface morphology, chemical components and mechanical properties of the cathode interphase layer, which are pivotal for the performance optimization of SSLBs.

Surface Modification of LiNi0.8 Co0.15 Al0.05 O2 Particles via Li3 PO4 Coating to Enable Aqueous Electrode Processing.

The successful implementation of an aqueous‐based electrode manufacturing process for nickel‐rich cathode active materials is challenging due to their high water sensitivity. In this work, the surface of LiNi0.8Co0.15Al0.05O2 (NCA) was modified with a lithium phosphate coating to investigate its ability to protect the active material during electrode production. The results illustrate that the coating amount is crucial and a compromise has to be made between protection during electrode processing and sufficient electronic conductivity through the particle surface. Cells with water‐based electrodes containing NCA with an optimized amount of lithium phosphate had a slightly lower specific discharge capacity than cells with conventional N‐methyl‐2‐pyrrolidone‐based electrodes. Nonetheless, the cells with optimized water‐based electrodes could compete in terms of cycle life.

Constructing effective TiO2 nano-coating for high-voltage Ni-rich cathode materials for lithium ion batteries by precise kinetic control

In order to improve the performance of Ni-rich cathode materials for lithium-ion batteries at high cut-off voltage, a highly effective TiO2 nano-coating is constructed on the surface of LiNi0.8Co0.1Mn0.1O2 by precisely controlling the hydrolytic dynamics of Ti4+, and the effect of this coating layer is systematically studied, especially at high upper cut-off voltage. The continuous TiO2 nano-coating layer provides a complete protection for LiNi0.8Co0.1Mn0.1O2 particles and enhances the reversibility of the phase transition between hexagonal and hexagonal (H2→H3) during cycling, which guarantees an excellent cycling stability under high upper cut-off voltage up to 4.5 V. Electrochemical impedance spectroscopy results confirm a stable interface between electrolyte and electrode and the fast kinetics at the surface of the modified sample. High Resolution Transmission Electron Microscopy (HR-TEM) measurement for the cycled electrodes further verifies the slight structure decay of the coated sample comparing with the pristine one. Thus, the modified sample presents excellent cycling stability with capacity retention of 72.2% after 500 cycles and 63.4% after 1000 cycles with the upper cut-off voltage of 4.5 V and 4.3 V, respectively. This work provides a universal method to prepare conformal TiO2 nano-coating and also offer guidance to properly evaluate the function of a coating.

TiO2-coated LiNi0.9Co0.08Al0.02O2 cathode materials with enhanced cycle performance for Li-ion batteries

Ni-rich cathode material is one of the most promising materials for Li-ion batteries in electric vehicles. However, fading capacity, poor cyclic stability and high pH value are still major challenges, which suppress its practical application. In this study, spherical LiNi0.9Co0.08Al0.02O2 powders with 0.4 wt% TiO2 coating layer were prepared by impregnation–hydrolysis method. Scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) results show that TiO2 is uniformly coated on the surface of LiNi0.9Co0.08Al0.02O2 particle and slightly embedded into LiNi0.9Co0.08Al0.02O2 particles. After 100 cycles at 2.0C, 0.4 wt% TiO2-coated LiNi0.9Co0.08Al0.02O2 electrode delivers much higher discharge capacity retention (77.0%) than the pristine LiNi0.9Co0.08Al0.02O2 electrode (63.3%). The excellent cycling performance of 0.4 wt% TiO2-coated LiNi0.9Co0.08Al0.02O2 electrode at a high discharge ratio is due to a TiO2 coating layer which can effectively reduce the direct contact between cathode material and electrolyte, suppress the oxidation of electrolyte, improve electrical conductivity of the electrode and increase the stability of the structure. With the increase of current density, TCNC sample clearly exhibits enhanced cycling performance with higher capacity retention, and the capacity retention of TCNC increases by 22% at 2.0 C.

Improving Interfacial Problems between the Cathode and Solid-State Electrolyte by Coating ETPTA-PEG onto the Surface of LiNi0.8Co0.1Mn0.1O2

Improving Interfacial Problems between the Cathode and Solid-State Electrolyte by Coating ETPTA-PEG onto the Surface of LiNi0.8Co0.1Mn0.1O2

In situ formed Li5AlO4-coated LiNi0·8Co0·1Mn0·1O2 cathode material assisted by hydrocarbonate with improved electrochemical performance for lithium-ion batteries

LiNi0·8Co0·1Mn0·1O2 has become a promising candidate as a cathode material of lithium ion batteries (LIBs) because of their high specific capacity, while the poor cycling and rate performances limit its commercial application. Herein, a thin layer of Li5AlO4 was in situ formed on the surface of LiNi0·8Co0·1Mn0·1O2 through a slow deposition process assisted by NaHCO3 and solid phase co-lithiation sintering. By employing the optimal amount (3 wt %) of Li5AlO4 coating on LiNi0·8Co0·1Mn0·1O2 cathode material (denoted as 3-NCM), the capacity retention rate of 3-NCM after 100 cycles increased from 75.06% to 89.15% at 2.8–4.3 V, and it also shows the most significantly enhanced rate performance. The outstanding electrochemical performance can be attributed to that the Li5AlO4 coating can impede the contact between the active materials and electrolyte, stabilize the material structure and inhibit the dissolution of transition metals during repeated charge–discharge cycles. And the superior conductivity of Li5AlO4 can improve the lithium ion diffusion rate. All these results connote that Li5AlO4-coated LiNi0·8Co0·1Mn0·1O2 cathode material might be employed in advanced lithium-ion batteries.

Protective electrode/electrolyte interphases for high energy lithium-ion batteries with p-toluenesulfonyl fluoride electrolyte additive

Abstract High energy density lithium-ion batteries using Ni-rich cathode (such as LiNi0.6Co0.2Mn0.2O2) suffer from severe capacity decay. P-toluenesulfonyl fluoride (pTSF) has been investigated as a novel film-forming electrolyte additive to enhance the cycling performances of graphite/LiNi0.6Co0.2Mn0.2O2 pouch cell. In comparison with the baseline electrolyte, a small dose of pTSF can significantly improve the cyclic stability of the cell. Theoretical calculations together with experimental results indicate that pTSF would be oxidized and reduced to construct protective interphase film on the surfaces of LiNi0.6Co0.2Mn0.2O2 cathode and graphite anode, respectively. These S-containing surface films derived from pTSF effectively mitigate the decomposition of electrolyte, reduce the interphasial impedance, as well as prevent the dissolution of transition metal ions from Ni-rich cathode upon cycling at high voltage. This finding is beneficial for the practical application of high energy density graphite/ LiNi0.6Co0.2Mn0.2O2 cells.

Regulating Surface and Grain-Boundary Structures of Ni-Rich Layered Cathodes for Ultrahigh Cycle Stability.

The wide applications of Ni-rich LiNi1- x-y Cox Mny O2 cathodes are severely limited by capacity fading and voltage fading during the cycling process resulting from the pulverization of particles, interfacial side reactions, and phase transformation. The canonical surface modification approach can improve the stability to a certain extent; however, it fails to resolve the key bottlenecks. The preparation of Li(Ni0.4 Co0.2 Mn0.4 )1- x Tix O2 on the surface of LiNi0.8 Co0.1 Mn0.1 O2 particles with a coprecipitation method is reported. After sintering, Ti diffuses into the interior and mainly distributes along surface and grain boundaries. A strong surface and grain boundary strengthening are simultaneously achieved. The pristine particles are fully pulverized into first particles due to mechanical instability and high strains, which results in serious capacity fading. In contrast, the strong surface and the grain boundary strengthening can maintain the structural integrity, and therefore significantly improve the cycle stability. A general and simple strategy for the design of high-performance Ni-rich LiNi1- x - y Cox Mny O2 cathode is provided and is applicable to surface modification and grain-boundary regulation of other advanced cathodes for batteries.

Surface architecture decoration on enhancing properties of LiNi0·8Co0·1Mn0·1O2 with building bi-phase Li3PO4 and AlPO4 by Al(H2PO4)3 treatment

As a promising cathode material, LiNi0·8Co0·1Mn0·1O2 has merits of relatively low cost and high discharge specific capacity, but its shortcoming of poor cycle stability restricts its extensive application. To improve the electrochemical performance of LiNi0·8Co0·1Mn0·1O2, Al(H2PO4)3 is used for surface treatment. Al(H2PO4)3 can react with residual lithium on the surface of LiNi0·8Co0·1Mn0·1O2 to build bi-phase Li3PO4 and AlPO4 coating layer (abbreviated as “LNCM@ALP”). This co-coating layer with good Li+ conductivity and chemical stability against the electrolyte, which significantly improved the cycling stability and rate performance of the material. Based on a series of characterization methods, it is proved that bi-phase Li3PO4 and AlPO4 coating layer co-exist on the surface of LiNi0·8Co0·1Mn0·1O2, and stabilize the structure of surface-modified sample LiNi0·8Co0·1Mn0·1O2. The electrochemical test has shown the cycle and rate performance of the LNCM@ALP sample has been significantly improved. After 100 cycles, the capacity of 0.5 wt% co-coated LNCM@ALP decreases from 182.8 mAh g−1 to 167.8 mAh g−1with the retention rate of 91.79% compared with bare LiNi0·8Co0·1Mn0·1O2 of only 82.66%. And at the discharge capacity of 0.5 wt% coated-samples are 162.5 mAh g−1 and 150.2 mAh g−1 at 5C, 10C, which shows an excellently rate performance.

Near-Equilibrium Control of Li2TiO3 Nanoscale Layer Coated on LiNi0.8Co0.1Mn0.1O2 Cathode Materials for Enhanced Electrochemical Performance.

Ni-rich layered metal oxide of LiNi0.8Co0.1Mn0.1O2 is a promising cathode material for next-generation lithium ion batteries because of its capability to deliver a high capacity; however, intrinsic problems, especially the side reactions between Ni4+ ions and the electrolyte, adversely affect its electrochemical and thermal stability. Surface coating by a protective and Li+-conducting Li2TiO3 layer is a strategic approach to remit those problems. The normal deposition strategies depend on the hydrolysis of titanium alkoxides, making it difficult to control the reaction equilibrium. Herein we report a near-equilibrium deposition tactic to achieve a uniform Li2TiO3 nanoscale layer coated on the surface of LiNi0.8Co0.1Mn0.1O2 microspheres to improve electrochemical performance and thermal stability. With pH modulation and BO33- scavenger in the (NH4)2TiF6 precursor solution, the ion product for the coating layer is controlled to be slightly bigger than its solubility product. The hydrolysis reaction chemistry can thus be manipulated at a near-equilibrium condition. Within the critical pH range of 4.8-5.2, a uniform coating layer of Li2TiO3 with the thickness of about 4 nm can be successfully deposited on the surface of the LiNi0.8Co0.1Mn0.1O2 cathode material, which greatly enhances its capacity retention to 93.5% after 200 cycles at 0.5 C. The appropriate Li2TiO3 coating can increase the mobility of Li ions and suppress the side reactions between electrolytes and cathode materials, which further makes the modified cathode display the higher peak temperature in differential scanning calorimetry analysis and capacity enhancement at 60 °C, which are related to safety concerns.

Superior Stability Secured by a Four-Phase Cathode Electrolyte Interface on a Ni-Rich Cathode for Lithium Ion Batteries.

A multifunctional coating with high ionic and electronic conductivity is constructed on the surface of LiNi0.8Co0.1Mn0.1O2 (NCM) to boost the battery stability upon cycling and during storage as well. Phosphoric acid reacts with residual lithium species on the pristine NCM to form a Li3PO4 coating with extra carbon nanotubes (CNTs) penetrating through, which shows high ionic and electronic conductivity. NCM, Li3PO4, CNTs, and the electrolyte jointly form a four-phase cathode electrolyte interface, which plays a key role in the great enhancement of capacity retention, from 50.3% for pristine NCM to 84.8% for the modified one after 500 cycles at 0.5C at room temperature. The modified NCM also delivers superior electrochemical performances at a high cut-off voltage (4.5 V), high temperature (55 °C), and high rate (10C). Furthermore, it can deliver 154.2 mA h g-1 at the 500th cycle after exposed to air with high humidity for 2 weeks. These results demonstrate that the well-constructed multifunctional coating can remarkably enhance the chemical and electrochemical performances of NCM. The improved cycling, storage, and rate performance are attributed to the four-phase cathode electrolyte interface delivering high electron and ionic conductivity and securing the cathode against attack. This work broadens the horizon for constructing effective electrode/electrolyte interfaces for electrochemical energy storage and conversion.

Enhancement on structural stability of Ni-rich cathode materials by in-situ fabricating dual-modified layer for lithium-ion batteries

Ni-rich cathodes have been considered as promising cathodes for Li-ion batteries (LIBs) because their high electrochemical capacities and low costs. However, fast capacity fading caused by interfacial instability and bulk structural degradation of Ni-rich cathodes during charge-discharge processes severely hinders their development and application. To address these challenges, we report a one-step dual-modification strategy to in-situ synthesize complex In2O3&LiInO2 co-coating layer on the surface of LiNi0.8Co0.1Mn0.1O2, which can cooperate collaboratively to stabilize layered structure and deplete lithium impurity. The dual-modified LiNi0.8Co0.1Mn0.1O2 materials not only show distinguished cycling stability at 1 C with a capacity retention of ca. 90%, but also exhibit a discharge capacity of 177.1 mAh g−1 at a high rate of 5 C with a capacity retention of 86.4% after 300 cycles. Further studies confirm structural degradation and intergranular cracks at the particle level can be effectively mitigated by uniformly adherent bi-functional coating layer even after long-term cycling. The results shed light on the feasibility of dual-modified strategy for improving the performance of Ni-rich cathode materials, which can also be applied to other oxide cathode materials.

Y2O3-decorated LiNi0.8Co0.15Al0.05O2 cathode material with improved electrochemical performance for lithium-ion batteries

The surface of LiNi0.8Co0.15Al0.05O2 (NCA) cathode material is modified with different percentages of Y2O3 through a wet chemical-calcination method to improve its electrochemical performance for using in lithium-ion batteries. The XRD results show that surface modification does not change the crystalline structure of NCA. The x wt% Y2O3-decorated (0.05 ≤ x ≤ 2) samples exhibit improved cyclability and rate-capability compared to pristine NCA. SEM images along with elemental mapping of Y show the uniform coverage of the NCA particles surface with yttrium oxide. The 1 wt% Y2O3-decorated NCA electrode exhibited a specific capacity of 181 mAh g−1 after 50 cycles at 0.5C, while that was 134 mAh g−1 for the pristine one. These specific capacities are equivalent to capacities retention of 93% and 69% for optimized electrode and pristine one, respectively. The enhanced electrochemical performance of the optimized Y2O3-decorated NCA is due to the protective and conducting roles of yttrium oxide, which are clearly manifested in the results of electrochemical impedance spectrometry. Yttrium oxide, by the surface modification of the active material, diminishes the side reactions between NCA particles and the electrolyte. Besides, yttrium oxide increases the electrical conductivity of the electrode by establishing a good electrical connection with the active material.