Li-Nb-O Coating/Substitution Enhances the Electrochemical Performance of the LiNi0.8Mn0.1Co0.1O2 (NMC 811) Cathode

Enhancing the Electrochemical Performances of Disordered Li1.23Ni0.3Nb0.3Fe0.16O0.85F0.15 Cathode Material for Lithium-Ion Batteries by LiNbOx Coating

For the next generation of lithium-ion batteries (LIBs), it is primary to seek high capacity and long-lifetime electrode materials. Li-excess disordered rock-salt structure (DRS) cathodes have gained much attention due to their high specific capacity. However, Li-excess can lead to a decrease in the structural stability of an electrode material. A new Li-rich DRS oxyfluorides, Li1.23Ni0.3Nb0.3Fe0.16O0.85F0.15 (F0.15) with a series amounts of LiNbOx (LN) coating (0, 5, 10, and 15 wt % denoted as F0.15-LN0, F0.15-LN5, F0.15-LN10, and F0.15-LN15, respectively), are successfully synthesized and evaluated as cathode materials in LIBs. Among them, F0.15-LN10 exhibits the highest initial discharge specific capacity of 296.1 mAh g-1 (at a current density of 20 mA g-1) with the capacity retention rate of 14% higher than that of the uncoated F0.15 after 80 cycles. Even at 300 mA g-1, F0.15-LN10 still delivers the highest discharge specific capacity of 130 mAh g-1. After 20 cycles, the charge-transfer impedance of F0.15-LN10 remained the smallest. The characterizations indicate that LN coating reduces the surface polarization of the cathode materials, slows the interfacial side reactions between the electrolyte and the electrode, and speeds up the Li+ diffusion. These results demonstrate that LN coating is an effective strategy to improve the electrochemical performance.

Artificial Layer Construction via Cosolvent Enables Stable Ni-Rich Cathodes for Enhanced Lithium Storage

Ni-rich cathodes have recently gained significant attention as next-generation cathodes for lithium-ion batteries. However, their relatively high oxidative surface should be reduced to control the high surface reactivity because the capacity retention decreases rapidly in the batteries. Herein, a simple and effective method to pretreat LiNi0.8Mn0.1Co0.1O2 (NMC811) particles using a cosolvent for improving the battery performance is reported. Imitating the interfacial reaction in practical cells, an artificial layer is created via a spontaneous redox reaction between the cathode and the organic solvent. The artificial layer comprises metal-organic compounds with reduced transition-metal cations. Benefiting from the artificial layer, the cells deliver high capacity retention at a high current density and better rate capability, which might result from the low and stable interfacial resistance of the modified NMC811 cathode. Our approach can effectively reduce the high oxidative surface of most oxide cathode materials and induce a long cyclic lifespan and high capacity retention in most battery systems.

Fast cycling of lithium metal in solid-state batteries by constriction-susceptible anode materials

Interface reaction between lithium (Li) and materials at the anode is not well understood in an all-solid environment. This paper unveils a new phenomenon of constriction susceptibility for materials at such an interface, the utilization of which helps facilitate the design of an active three-dimensional scaffold to host rapid plating and stripping of a significant amount of a thick Li metal layer. Here we focus on the well-known anode material silicon (Si) to demonstrate that, rather than strong Li-Si alloying at the conventional solid-liquid interface, the lithiation reaction of micrometre-sized Si can be significantly constricted at the solid-solid interface so that it occurs only at thin surface sites of Si particles due to a reaction-induced, diffusion-limiting process. The dynamic interaction between surface lithiation and Li plating of a family of anode materials, as predicted by our constrained ensemble computational approach and represented by Si, silver (Ag) and alloys of magnesium (Mg), can thus more homogeneously distribute current densities for the rapid cycling of Li metal at high areal capacity, which is important in regard to solid-state battery application.

Ni-rich lithium nickel manganese cobalt oxide cathode materials: A review on the synthesis methods and their electrochemical performances

The demand for lithium-ion batteries (LIBs) has skyrocketed due to the fast-growing global electric vehicle (EV) market. The Ni-rich cathode materials are considered the most relevant next-generation positive-electrode materials for LIBs as they offer low cost and high energy density materials. However, by increasing Ni content in the cathode materials, the materials suffer from poor cycle ability, rate capability and thermal stability. Therefore, this review article focuses on recent advances in the controlled synthesis of lithium nickel manganese cobalt oxide (NMC). This work highlights the advantages and challenges associated with each synthesis method that has been used to produce Ni-rich materials. The crystallography and morphology obtained are discussed, as the performance of LIBs is highly dependent on these properties. To address the drawbacks of Ni-rich cathode materials, certain modifications such as ion doping, and surface coating have been pursued. The correlation between the synthesized and modified NMC materials with their electrochemical performances is summarized. Several gaps, challenges and guidelines are elucidated here in order to provide insights for facilitating research in high-performance cathode for lithium-ion batteries. Factors that govern the formation of nickel-rich layered cathode such as pH, reaction and calcination temperatures have been outlined and discussed.

Enabling Electrochemical-Mechanical Robustness of Ultra-High Ni Cathode via Self-Supported Primary-Grain-Alignment Strategy

The electrochemical-mechanical degradation of ultrahigh Ni cathode for lithium-ion batteries is a crucial aspect that limits the cycle life and safety of devices. Herein, the study reports a facile strategy involving rational design of primary grain crystallographic orientation within polycrystalline cathode, which well enhanced its electro-mechanical strength and Li+ transfer kinetics. Ex situ and in situ experiments/simulations including cross-sectional particle electron backscatter diffraction (EBSD), single-particle micro-compression, thermogravimetric analysis combined with mass spectrometry (TGA-MS), and finite element modeling reveal that, the primary-grain-alignment strategy effectively mitigates the particle pulverization, lattice oxygen release thereby enhances battery cycle life and safety. Besides the preexisting doping and coating methodologies to improve the stability of Ni-rich cathode, the primary-grain-alignment strategy, with no foreign elements or heterophase layers, is unprecedently proposed here. The results shed new light on the study of electrochemical-mechanical strain alleviation for electrode materials.

Revealing the effect of Nb5+ on the electrochemical performance of nickel-rich layered LiNi0.83Co0.11Mn0.06O2 oxide cathode for lithium-ion batteries

The layered Nb⁵⁺-doped LiNi_0.83Co_0.11Mn_0.06O₂ (NCM) oxide cathode materials are successfully synthesized through introducing Nb₂O₅ into the precursor Ni_0.83Co_0.11Mn_0.06(OH)₂ during the lithiation process. The results refined by GSAS software present that the Nb⁵⁺-doped samples possess the perfect crystal structure with broader Li⁺ diffusion pathways. Moreover, the morphology characterized by scanning electron microscope displays the compact secondary particles packed by smaller primary particles under the effect of Nb⁵⁺. The excellent electrochemical properties are also acquired from the Nb⁵⁺-doped samples, in which the optimal rate performance and cycling stability are performed for NCM-1.0 when up to 1.0 mol % of Nb₂O₅ (based on the precursor) is added. Benefited from the introduction of Nb⁵⁺, the cell assembled with the NCM-1.0 electrode retains higher capacity retention of 86.6 % at 1.0 C and 25 °C, and 71.7 % at 1.0 C and 60 °C after 200cycles. Moreover, it also delivers higher discharge specific capacity of 154.6 mAh g^-1 at 5.0 C. Therefore, the Nb⁵⁺-doping strategy may open an effective route for optimizing nickel-rich oxide cathode materials, which is worth popularizing for the enhancement of the electrochemical performance of nickel-rich cathodes for lithium-ion batteries.

Achieving structural stability and enhanced electrochemical performance through Nb-doping into Li- and Mn-rich layered cathode for lithium-ion batteries

Although Li- and Mn-rich layered oxides are attractive cathode materials possessing high energy densities, they have not been commercialized owing to voltage decay, low rate capability, poor capacity retention, and high irreversible capacity in the first cycle. To circumvent these issues, we propose a Li_1.2Ni_0.13Co_0.13Mn_0.53Nb_0.01O₂ (Nb-LNCM) cathode material, wherein Nb doping strengthens the transition metal oxide (TM-O) bond and alleviates the anisotropic lattice distortion while stabilizing the layered structure. During long-term cycling, maintaining a wider LiO₆ interslab thickness in Nb-LNCM creates a favorable Li⁺ diffusion path, which improves the rate capability. Moreover, Nb doping can decrease oxygen loss, suppress the phase transition from layered to spinel and rock-salt structures, and relieve structural degradation. Nb doping results in less capacity contributions of Mn and Co and more reversible Ni and O redox reactions compared to pristine Li_1.2Ni_0.133Co_0.133Mn_0.533O₂ (LNCM), which significantly mitigates the voltage decay (Δ0.289 and Δ0.516 V for Nb-LNCM and LNCM, respectively) and ensures stable capacity retention (82.7 and 70.3% for Nb-LNCM and LNCM, respectively) during the initial 100 cycles. Our study demonstrates that Nb doping is an effective and practical strategy to enhance the structural and electrochemical integrity of Li- and Mn-rich layered oxides. This promotes the development of stable cathode materials for high-energy-density lithium-ion batteries.

Recent achievements toward the development of Ni-based layered oxide cathodes for fast-charging Li-ion batteries

The driving mileage of electric vehicles (EVs) has been substantially improved in recent years with the adoption of Ni-based layered oxide materials as the battery cathode. The average charging period of EVs is still time-consuming, compared with the short refueling time of an internal combustion engine vehicle. With the guidance from the United States Department of Energy, the charging time of refilling 60% of the battery capacity should be less than 6 min for EVs, indicating that the corresponding charging rate for the cathode materials is to be greater than 6C. However, the sluggish kinetic conditions and insufficient thermal stability of the Ni-based layered oxide materials hinder further application in fast-charging operations. Most of the recent review articles regarding Ni-based layered oxide materials as cathodes for lithium-ion batteries (LIBs) only touch degradation mechanisms under slow charging conditions. Of note, the fading mechanisms of the cathode materials for fast-charging, of which the importance abruptly increases due to the development of electric vehicles, may be significantly different from those of slow charging conditions. There are a few review articles regarding fast-charging; however, their perspectives are limited mostly to battery thermal management simulations, lacking experimental validations such as microscale structure degradations of Ni-based layered oxide cathode materials. In this review, a general and fundamental definition of fast-charging is discussed at first, and then we summarize the rate capability required in EVs and the electrochemical and kinetic properties of Ni-based layered oxide cathode materials. Next, the degradation mechanisms of LIBs leveraging Ni-based cathodes under fast-charging operation are systematically discussed from the electrode scale to the particle scale and finally the atom scale (lattice oxygen-level investigation). Then, various strategies to achieve higher rate capability, such as optimizing the synthesis process of cathode particles, fabricating single-crystalline particles, employing electrolyte additives, doping foreign ions, coating protective layers, and engineering the cathode architecture, are detailed. All these strategies need to be considered to enhance the electrochemical performance of Ni-based oxide cathode materials under fast-charging conditions.

Fabricating Heterostructures for Boosting the Structure Stability of Li-Rich Cathodes

Li-rich Mn-based oxides are regarded as the most promising new-generation cathode materials, but their practical application is greatly hindered by structure collapse and capacity degradation. Herein, a rock salt phase is epitaxially constructed on the surface of Li-rich Mn-based cathodes through Mo doping to improve their structural stability. The heterogeneous structure composed of a rock salt phase and layered phase is induced by Mo⁶⁺ enriched on the particle surface, and the strong Mo-O bonding can enhance the TM-O covalence. Therefore, it can stabilize lattice oxygen and inhibit the side reaction of the interface and structural phase transition. The discharge capacity of 2% Mo-doped samples (Mo 2%) displays 279.67 mA h g^-1 at 0.1 C (vs 254.39 mA h g^-1 (pristine)), and the discharge capacity retention rate of Mo 2% is 79.4% after 300 cycles at 5 C (vs 47.6% (pristine)).

In situ Interweaved Binder Framework Mitigating the Structural and Interphasial Degradations of High-nickel Cathodes in Lithium-ion Batteries

The practical viability of high-nickel layered oxide cathodes is compromised by the interphasial and structural degradations. Herein, we demonstrate that by applying an in situ interweaved binder, the cycling stability of high-nickel cathodes can be significantly improved. Specifically, the results show that the resilient binder network immobilizes the transition-metal ions, suppresses electrolyte oxidative decomposition, and mitigates cathode particles pulverization, thus resulting in suppressed cathode-to-anode chemical crossover and ameliorated chemistry and architecture of electrode-electrolyte interphases. Pouch full cells with high-mass-loading LiNi_0.8 Mn_0.1 Co_0.1 O₂ cathodes achieve 0.02 % capacity decay per cycle at 1 C rate over 1 000 deep cycles at 4.4 V (vs. graphite). This work demonstrates a rational structural and compositional design strategy of polymer binders to mitigate the structural and interphasial degradations of high-Ni cathodes in lithium-ion batteries.

Surface Stabilization of Cobalt-Free LiNiO2 with Niobium for Lithium-Ion Batteries

Lithium nickel oxide (LiNiO₂) is a promising next-generation cathode material for lithium-ion batteries (LIBs), offering exceptionally high specific capacity and reduced material cost. However, the poor structural, surface, and electrochemical stabilities of LiNiO₂ result in rapid loss of capacity during prolonged cycling, making it unsuitable for application in commercial LIBs. Herein, we demonstrate that incorporation of a small amount of niobium effectively suppresses the structural and surface degradation of LiNiO₂. The niobium-treated LiNiO₂ retains 82% of its initial capacity after 500 cycles in full cells with a graphite anode compared to 73% for untreated LiNiO₂. We utilize a facile method for incorporating niobium, which yields Li_xNbO_y phase formation as a surface coating on the primary particles. Through a combination of X-ray diffraction, electron microscopy, and electrochemical analyses, we show that the resulting niobium coating reduces active material loss over long-term cycling and enhances lithium-ion diffusion kinetics. The enhanced structural integrity and electrochemical performance of the niobium-treated LiNiO₂ are correlated to a reduction in the formation of nanopore defects during cycling compared to the untreated LiNiO₂.

Controlled Synthesis of Single-Crystalline Ni-Rich Cathodes for High-Performance Lithium-Ion Batteries

Single-crystalline LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) has been considered as one of the most promising cathode materials. It addresses the pulverization issue present in its polycrystalline counterpart by eliminating intergranular cracks. However, synthesis of high-performance single-crystalline NCM is still a challenge owing to the lower structure stability of NCM811 at high calcination temperatures (≥900 °C), which is often required to grow single crystals. Herein, we report a synthesis process for microsized single-crystalline NCM811 particles with exposed (010) facets on their lateral sides [named as SC-NCM(010)], which includes the preparation of a well-dispersed microblock-like Ni_0.8Co_0.1Mn_0.1(OH)₂ precursor through coprecipitation assisted with addition of PVP and Na₂SiO₃ and subsequent lithiation of the precursor at 800 °C. The SC-NCM(010) cathode exhibits an excellent capacity retention rate (91.6% after 200 cycles at 1 C, 4.3 V) and a high rate capability (152.2 mAh/g at 20 C, 4.4 V), much superior to those of polycrystalline NCM811 cathodes. However, despite the removal of interparticle boundaries, when cycled between 2.8 and 4.5 V, the SC-NCM(010) cathode still suffers from structural changes including lattice gliding and intragranular cracking. These structural changes are correlated with the interior structural inhomogeneity, which is evidenced by the coexistence of H2 and H3 phases in the fully deintercalated state.

Single-Crystal Nickel-Based Cathodes: Fundamentals and Recent Advances

Lithium-ion batteries (LIBs) represent the most promising choice for meeting the ever-growing demand of society for various electric applications, such as electric transportation, portable electronics, and grid storage. Nickel-rich layered oxides have largely replaced LiCoO2 in commercial batteries because of their low cost, high energy density, and good reliability. Traditional nickel-based oxide particles, usually called polycrystal materials, are composed of microsized primary particles. However, polycrystal particles tend to suffer from pulverization and severe side reactions along grain boundaries during cycling. These phenomena accelerate cell degradation. Single-crystal materials, which exhibit robust mechanical strength and a high surface area, have great potential to address the challenges that hinder their polycrystal counterparts. A comprehensive understanding of the growing body of research related to single-crystal materials is imperative to improve the performance of cathodes in LIBs. This review highlights origins, recent developments, challenges, and opportunities for single-crystal layered oxide cathodes. The synthesis science behind single-crystal materials and comparative studies between single-crystal and polycrystal materials are discussed in detail. Industrial techniques and facilities are also reviewed in combination with our group’s experiences in single-crystal research. Future development should focus on facile production with strong control of the particle size and distribution, structural defects, and impurities to fully reap the benefits of single-crystal materials.

Graphical abstract

Effects of Coating on the Electrochemical Performance of a Nickel-Rich Cathode Active Material

: Due to their safety and high power density, one of the most promising types of all-solid-state lithium batteries is the one made with the argyrodite solid electrolyte (ASE). Although substantial efforts have been made toward the commercialization of this battery, it is still challenged by some technical issues. One of these issues is to prevent the side reactions at the interface of the ASE and the cathode active material (CAM). A solution to address this issue is to coat the CAM particles with a material that is compatible with both ASE and CAM. Prior studies show that the lithium niobate, LiNbO3, (LNO) is a promising material for coating CAM particles to reduce the interfacial side reactions. However, no systematic study is available in the literature to show the effect of coating LNO on CAM performance. This paper aims to quantify the effect of LNO coating on the electrochemical performance of a nickel-rich CAM. The electrochemical performance parameters that are studied are the capacity, cycling performance, and rate performance of the coated-CAM; and the effectiveness of the coating to prevent the side reactions at the ASE and CAM interface is out of the scope of this study. To eliminate the effect of side reactions at the ASE and CAM interface, we conduct all tests in the organic liquid electrolyte (OLE) cells to solely present the effect of coating on the CAM performance. For this purpose, 0.5 wt% and 1 wt% LNO are used to coat the LiNi0.6Mn0.2Co0.2O2 (NMC-60) CAM through two synthesizing methods. Consequently, the effects of the synthesizing method and the coating weight percentage on the NMC-60 performance are presented.

A Two-Parameter Space to Tune Solid Electrolytes for Lithium Dendrite Constriction

Li dendrite penetration, and associated microcrack propagation, at high current densities is one main challenge to the stable cycling of solid-state batteries. The interfacial decomposition reaction between Li dendrite and a solid electrolyte was recently used to suppress Li dendrite penetration through a novel effect of "dynamic stability". Here we use a two-parameter space to classify electrolytes and propose that the effect may require the electrolyte to occupy a certain region in the space, with the principle of delicately balancing the two property metrics of a sufficient decomposition energy with the Li metal and a low critical mechanical modulus. Furthermore, in our computational prediction prepared using a combination of high-throughput computation and machine learning, we show that the positions of electrolytes in such a space can be controlled by the chemical composition of the electrolyte; the compositions can also be attained by experimental synthesis using core-shell microstructures. The designed electrolytes following this principle further demonstrate stable long cycling from 10 000 to 20 000 cycles at high current densities of 8.6-30 mA/cm² in solid-state batteries, while in contrast the control electrolyte with a nonideal position in the two-parameter space showed a capacity decay that was faster by at least an order of magnitude due to Li dendrite penetration.

Precise surface control of cathode materials for stable lithium-ion batteries

The increasing demand for high-energy Li-ion batteries (LIBs) continues to push the development of electrode materials, particularly cathode materials, towards their capacity limits. Despite the enormous success, the stability and reliability of LIBs are becoming a serious concern due to the much-aggravated side reactions between electrode materials and organic electrolytes. How to stabilize the cathode/electrolyte interface is therefore an imperative and urgent task drawing considerable attention from both academia and industry. An active treatment on the surface of cathode materials, usually by introducing an inert protection layer, to diminish their side reaction with electrolytes turns out to be a reasonable and effective strategy. This Feature Article firstly outlines our synthesis efforts for the construction of a uniform surface nanocoating on various cathode materials. Different wet chemical routes have been designed to facilitate the control of growth kinetics of targeted coating species so that a precise surface coating could be achieved with nanometer accuracy. Furthermore, we showed the possibility to transform the outer coating layer into a surface doping effect through surface solid reaction at high temperature. A detailed discussion on the structure-performance relationship of these surface-controlled cathode materials is introduced to probe the stabilization mechanism. Finally, perspectives on the development tendency of high-energy cathodes for stable LIBs are provided.

Improving Fast Charging-Discharging Performances of Ni-Rich LiNi0.8Co0.1Mn0.1O2 Cathode Material by Electronic Conductor LaNiO3 Crystallites

Fast charging-discharging is one of the important requirements for next-generation high-energy Li-ion batteries, nevertheless, electrons transport in the active oxide materials is limited. Thus, carbon coating of active materials is a common method to supply the routes for electron transport, but it is difficult to synthesize the oxide-carbon composite for LiNiO₂-based materials which need to be calcined in an oxygen-rich atmosphere. In this work, LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) coated with electronic conductor LaNiO₃ (LNO) crystallites is demonstrated for the first time as fast charging-discharging and high energy cathodes for Li-ion batteries. The LaNiO₃ succeeds in providing an exceptional fast charging-discharging behavior and initial coulombic efficiency in comparison with pristine NCM811. Consequently, the NCM811@3LNO electrode presents a higher capacity at 0.1 C (approximately 246 mAh g⁻¹) and a significantly improved high rate performance (a discharge specific capacity of 130.62 mAh g⁻¹ at 10 C), twice that of pristine NCM811. Additionally, cycling stability is also improved for the composite material. This work provides a new possibility of active oxide cathodes for high energy/power Li-ion batteries by electronic conductor LaNiO₃ coating.

Improvement of the Electrochemical Performance of LiNi0.8Co0.1Mn0.1O2 via Atomic Layer Deposition of Lithium-Rich Zirconium Phosphate Coatings

Owing to its high energy density, LiNi_0.8Co_0.1Mn_0.1O₂ (NMC811) is a cathode material of prime interest for electric vehicle battery manufacturers. However, NMC811 suffers from several irreversible parasitic reactions that lead to severe capacity fading and impedance buildup during prolonged cycling. Thin surface protection films coated on the cathode material mitigate degradative chemomechanical reactions at the electrode-electrolyte interphase, which helps to increase cycling stability. However, these coatings may impede the diffusion of lithium ions, and therefore, limit the performance of the cathode material at a high C-rate. Herein, we report on the synthesis of zirconium phosphate (Zr_xPO_y) and lithium-containing zirconium phosphate (Li_xZr_yPO_z) coatings as artificial cathode-electrolyte interphases (ACEIs) on NMC811 using the atomic layer deposition technique. Upon prolonged cycling, the Zr_xPO_y- and Li_xZr_yPO_z-coated NMC811 samples show 36.4 and 49.4% enhanced capacity retention, respectively, compared with the uncoated NMC811. Moreover, the addition of Li ions to the Li_xZr_yPO_z coating enhances the rate performance and initial discharge capacity in comparison to the Zr_xPO_y-coated and uncoated samples. Using online electrochemical mass spectroscopy, we show that the coated ACEIs largely suppress the degradative parasitic side reactions observed with the uncoated NMC811 sample. Our study demonstrates that providing extra lithium to the ACEI layer improves the cycling stability of the NMC811 cathode material without sacrificing its rate capability performance.

Synergy Effect of K Doping and Nb Oxide Coating on Li1.2Ni0.13 Co0.13Mn0.54O2 Cathodes

The Li-rich oxides are promising cathode materials due to their high energy density. However, characteristics such as low rate capability, unstable cyclic performance, and rapid capacity fading during cycling prevent their commercialization. These characteristics are mainly attributed to the phase instability of the host structure and undesirable side reactions at the cathode/electrolyte interface. To suppress the phase transition during cycling and interfacial side reactions with the reactive electrolyte, K (potassium) doping and Nb oxide coating were simultaneously introduced to a Li-rich oxide (Li1.2Ni0.13Co0.13Mn0.54O2). The capacity and rate capability of the Li-rich oxide were significantly enhanced by K doping. Considering the X-ray diffraction (XRD) analysis, the interslab thickness of LiO2 increased and cation mixing decreased due to K doping, which facilitated Li migration during cycling and resulted in enhanced capacity and rate capability. The K-doped Li-rich oxide also exhibited considerably improved cyclic performance, probably because the large K+ ions disturb the migration of the transition metals causing the phase transition and act as a pillar stabilizing the host structure during cycling. The Nb oxide coating also considerably enhanced the capacity and rate capability of the samples, indicating that the undesirable interfacial layer formed from the side reaction was a major resistance factor that reduced the capacity of the cathode. This result confirms that the introduction of K doping and Nb oxide coating is an effective approach to enhance the electrochemical performance of Li-rich oxides.

Conditioning the Surface and Bulk of High-Nickel Cathodes with a Nb Coating: An In Situ X-ray Study

Surface coating is commonly employed by industries to improve the cycling and thermal stability of high-nickel (Ni) transition metal (TM) layered cathodes for their practical use in lithium-ion batteries. Niobium (Nb) coating or substitution has been shown to be effective in stabilizing LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cathodes; in addition, the electrochemical performance of the final products varies depending on the postprocessing. In this follow-up study, we use in situ synchrotron X-ray diffraction to investigate the kinetic processes and the involved structural evolution in Nb-coated NMC811 upon heat treatment. Quantitative structure analysis reveals thermally driven concurrent changes in the bulk and surface, in particular, the phase evolution of the coating layer and Nb/TM interdiffusion that facilitates penetration of Nb into the bulk and particle growth at the increased temperatures. Findings from this study highlight the new opportunities for the intended control of the structure and surface properties of high-Ni cathodes through surface coating in conjunction with postprocessing.

Effects of doping high-valence transition metal (V, Nb and Zr) ions on the structure and electrochemical performance of LIB cathode material LiNi0.8Co0.1Mn0.1O2

Ni-rich layered oxides, like LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811), have been widely investigated as cathodes due to their high energy density. However, gradual structural transformation during cycling can lead to capacity degradation and potential decay of cathode materials. Herein, we doped high-valence transition metal (TM) ions (V⁵⁺, Nb⁵⁺, and Zr⁴⁺) at the Ni site of NCM811 by first principles simulations and explored the mechanism of doping TMs in NCMs for enhancing the electrochemical performance. Analysis of the calculations shows that doping V, Nb and Zr has an efficient influence on alleviating the Ni oxidation, reducing the loss of oxygen, and facilitating Li⁺ migration. Moreover, V doping can further suppress the lattice distortion due to the radius of V⁵⁺ being close to the radius of Mn⁴⁺. In particular, compared with the barrier of the pristine NCM in Li divacancy, the barrier of V-doped NCM reaches the lowest. In conclusion, V is the most favorable dopant for NCM811 to improve the electrochemical properties and achieve both high capacity and cycling stability.

A dynamic stability design strategy for lithium metal solid state batteries

A solid-state electrolyte is expected to suppress lithium (Li) dendrite penetration with high mechanical strength^1-4. However, in practice it still remains challenging to realise a lithium metal anode for batteries, because micrometre- or submicrometre-sized cracks in ceramic pellets can frequently be generated during battery assembly or long-time cycling^3,5. Once cracks form, lithium dendrite penetration is inevitable^6,7. Here we describe a solid-state battery design with a hierarchy of interface stabilities (to lithium metal responses), to achieve an ultrahigh current density with no lithium dendrite penetration. Our multilayer design has the structure of a less-stable electrolyte sandwiched between more-stable solid electrolytes, which prevents any lithium dendrite growth through well localized decompositions in the less stable electrolyte layer. A mechanism analogous to the expansion screw effect is proposed, whereby any cracks are filled by dynamically generated decompositions that are also well constrained, probably by the 'anchoring' effect the decompositions induce. The cycling performance of the lithium metal anode paired with a LiNi_0.8Mn_0.1Co_0.1O₂ cathode is very stable, with an 82 per cent capacity retention after 10,000 cycles at a 20C rate (8.6 milliamps per centimetre squared) and 81.3 per cent capacity retention after 2,000 cycles at a 1.5C rate (0.64 milliamps per centimetre squared). Our design also enables a specific power of 110.6 kilowatts per kilogram and specific energy up to 631.1 watt hours per kilogram at the micrometre-sized cathode material level.

Studies of Nickel-Rich LiNi0.85Co0.10Mn0.05O2 Cathode Materials Doped with Molybdenum Ions for Lithium-Ion Batteries

In this work, we continued our systematic investigations on synthesis, structural studies, and electrochemical behavior of Ni-rich materials Li[NixCoyMnz]O2 (x + y + z = 1; x ≥ 0.8) for advanced lithium-ion batteries (LIBs). We focused, herein, on LiNi0.85Co0.10Mn0.05O2 (NCM85) and demonstrated that doping this material with high-charge cation Mo6+ (1 at. %, by a minor nickel substitution) results in substantially stable cycling performance, increased rate capability, lowering of the voltage hysteresis, and impedance in Li-cells with EC-EMC/LiPF6 solutions. Incorporation of Mo-dopant into the NCM85 structure was carried out by in-situ approach, upon the synthesis using ammonium molybdate as the precursor. From X-ray diffraction studies and based on our previous investigation of Mo-doped NCM523 and Ni-rich NCM811 materials, it was revealed that Mo6+ preferably substitutes Ni residing either in 3a or 3b sites. We correlated the improved behavior of the doped NCM85 electrode materials in Li-cells with a partial Mo segregation at the surface and at the grain boundaries, a tendency established previously in our lab for the other members of the Li[NixCoyMnz]O2 family.

Stabilization of a Highly Ni-Rich Layered Oxide Cathode through Flower-Petal Grain Arrays

Nickel adds to the capacity of layered oxide cathodes of lithium-ion batteries but comprises their stability. We report a petal-grained Li[Ni_0.89Co_0.10Sb_0.01]O₂ cathode that is, nevertheless, stable. The stability originates from the ordering of the nanosized grains in a dense, flower-petal-like array, where the elongated and nearly parallel grains radiate from the center to the surface. The ordering of the grains prevents microcrack generation from abrupt lattice changes of the stressful H2-H3 phase transition. The tight packing of the nanograins is conserved upon cycling, preventing destructive seepage of the electrolytic solution into the particles. The half-cell, cycling between 2.7-4.3 V versus Li/Li⁺ at a 0.5 C rate retains 95.0% of its initial capacity of 220 mAh g^-1 after 100 cycles. The full-cell, cycling with a graphite anode and between 3.0-4.2 V at a 1 C rate, retains 83.9% of its initial capacity after 1000 cycles.

Ni-Rich Layered Oxide with Preferred Orientation (110) Plane as a Stable Cathode Material for High-Energy Lithium-Ion Batteries

The cathode, a crucial constituent part of Li-ion batteries, determines the output voltage and integral energy density of batteries to a great extent. Among them, Ni-rich LiNi_xCo_yMn_zO₂ (x + y + z = 1, x ≥ 0.6) layered transition metal oxides possess a higher capacity and lower cost as compared to LiCoO₂, which have stimulated widespread interests. However, the wide application of Ni-rich cathodes is seriously hampered by their poor diffusion dynamics and severe voltage drops. To moderate these problems, a nanobrick Ni-rich layered LiNi_0.6Co_0.2Mn_0.2O₂ cathode with a preferred orientation (110) facet was designed and successfully synthesized via a modified co-precipitation route. The galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) analysis of LiNi_0.6Co_0.2Mn_0.2O₂ reveal its superior kinetic performance endowing outstanding rate performance and long-term cycle stability, especially the voltage drop being as small as 67.7 mV at a current density of 0.5 C for 200 cycles. Due to its unique architecture, dramatically shortened ion/electron diffusion distance, and more unimpeded Li-ion transmission pathways, the current nanostructured LiNi_0.6Co_0.2Mn_0.2O₂ cathode enhances the Li-ion diffusion dynamics and suppresses the voltage drop, thus resulting in superior electrochemical performance.

NCA, NCM811, and the Route to Ni-Richer Lithium-Ion Batteries

The aim of this article is to examine the progress achieved in the recent years on two advanced cathode materials for EV Li-ion batteries, namely Ni-rich layered oxides LiNi0.8Co0.15Al0.05O2 (NCA) and LiNi0.8Co0.1Mn0.1O2 (NCM811). Both materials have the common layered (two-dimensional) crystal network isostructural with LiCoO2. The performance of these electrode materials are examined, the mitigation of their drawbacks (i.e., antisite defects, microcracks, surface side reactions) are discussed, together with the prospect on a next generation of Li-ion batteries with Co-free Ni-rich Li-ion batteries.