Single Crystal LiNi0 Research Articles

Restraining Planar Gliding in Single-Crystalline LiNi0.9Co0.05Mn0.05O2 Cathodes by Combining Bulk and Surface Modification Strategies.

The delamination cracking from planar gliding along the (003) facets and anisotropic lattice strain perpendicular to the (003) facets inevitable lead to degradation of Ni-rich single-crystal cathode materials, adversely affecting their cyclability. Herein, we rationally design a single-crystal LiNi0.9Co0.05Mn0.05O2 (SC90) cathode with robust chemo-mechanical properties, in which coherently grown MgO6 octahedra and BO4 tetrahedra are incorporated into the lattice, and a stabilizing Mg3(BO3)2 layer is concurrently formed on the particle surface. Multiscale in/ex situ characterizations and theoretical calculations indicate that introducing the MgO6 and BO4 units leads to a "pinning effect" within the layered structure. This in turn strongly mitigates mechanical degradation by reducing planar gliding and delamination cracking over extended cycling. Moreover, the Mg3(BO3)2 coating maintains fast lithium diffusion by suppressing parasitic reactions at the cathode|electrolyte interface. The tailored SC90 cathode exhibits a capacity retention of ~88% after 300 cycles at 5C rate, significantly outperforming the pristine counterpart (~60%). Additionally, a pouch-type full cell with a graphite anode sustains a specific discharge capacity of 177 mAh g-1 after 500 cycles, with 90% capacity retention. This work highlights the "pining effect" in preventing unfavorable slab sliding and structural deterioration, offering new insights for designing advanced ultrahigh Ni single-crystal cathodes.

Eliminating chemo-mechanical degradation of lithium solid-state battery cathodes during >4.5 V cycling using amorphous Nb2O5 coatings.

Lithium solid-state batteries offer improved safety and energy density. However, the limited stability of solid electrolytes (SEs), as well as irreversible structural and chemical changes in the cathode active material, can result in inferior electrochemical performance, particularly during high-voltage cycling (>4.3 V vs Li/Li+). Therefore, new materials and strategies are needed to stabilize the cathode/SE interface and preserve the cathode material structure during high-voltage cycling. Here, we introduce a thin (~5 nm) conformal coating of amorphous Nb2O5 on single-crystal LiNi0.5Mn0.3Co0.2O2 cathode particles using rotary-bed atomic layer deposition (ALD). Full cells with Li4Ti5O12 anodes and Nb2O5-coated cathodes demonstrate a higher initial Coulombic efficiency of 91.6% ± 0.5% compared to 82.2% ± 0.3% for the uncoated samples, along with improved rate capability (10x higher accessible capacity at 2C rate) and remarkable capacity retention during extended cycling (99.4% after 500 cycles at 4.7 V vs Li/Li+). These improvements are associated with reduced cell polarization and interfacial impedance for the coated samples. Post-cycling electron microscopy analysis reveals that the Nb2O5 coating remains intact and prevents the formation of spinel and rock-salt phases, which eliminates intra-particle cracking of the single-crystal cathode material. These findings demonstrate a potential pathway towards stable and high-performance solid-state batteries during high-voltage operation.

Study on the surface modification of regenerated and repaired LiNi0.5Co0.2Mn0.3O2 single crystal

Due to the relatively small particle size of single crystals, the high specific surface area increases the side reactions between the electrode and the electrolyte. Without proper surface modification, single-crystal particles tend to interact directly with the electrolyte, leading to side reactions that impair the electrochemical performance of the material. To address this issue, constructing a coating layer on the material's surface is one effective solution. In this study, a wet-coating technique was employed to co-coat single-crystal LiNi0.5Co0.2Mn0.3O2 cathode material with vanadium (V) and samarium (Sm). SEM and TEM tests revealed the presence of a V-Sm coating layer with a thickness of approximately 1–3 nm on the surface of the coated samples. The coated material demonstrated a capacity retention rate of 86.5 % after 450 cycles at a 1 C rate (1 C = 160 mA h g−1), which represents an improvement of about 6.7 % compared to the original material. EIS results indicated that the V-Sm coating stabilized the surface SEI film of the material and inhibited the growth of charge transfer resistance (Rct). XPS analysis of the electrodes after cycling showed that the V-Sm coating effectively protected the material by isolating it from direct contact with the electrolyte, suppressing the decomposition of the electrolyte during cycling, and reducing adverse side reactions between the material and the electrolyte, thereby enhancing the overall electrochemical performance of the material.

Suppressing high voltage chemo-mechanical degradation in single crystal nickel-rich cathodes for high-performance all-solid-state lithium batteries

Sulfide-based all-solid-state lithium batteries (SASSLBs) suffer from electrochemo.mechanical damage to Ni-rich oxide-based cathode active materials (CAMs), primarilycaused by severe volume changes, results in significant stress and strain cuase micro-cracks, and interfacial contact loss at potentials > 4.3 V(vs. Li/Li+). Quantifying micro-cracks and voids in cathode active materials (CAMs) can reveal the degradation mechanisms of Ni-rich oxide-based cathodes during electrochemical cycling. Nonetheless, the origin of electrochemical-mechanical damage remains unclear. Herein, We have developed a multifunctional PEG-based soft buffer layer (SBL) on the surface of carbon black (CB). This layer functions as a percolation network in the single crystal LiNi0.83Co0.07Mn0.1O2 and Li6PS5Cl composite cathode layer, ensuring superior ionic conductivity, reducing void formation and particle cracking, and promoting uniform utilization of the cathode active material in all-solid-state lithium batteries (ASSLBs). STEM-HAADF combined with nanoscale X-ray holo-tomography and plasma-focused ion beam scanning electron microscopy confirmed that the PEG-based SBL mitigated strain induced by reaction heterogeneity in the cathode. This strain produces lattice stretches, distortions, and the formation of curved transition metal oxide layers near the surface, contributing to structural degradation at elevated voltages. Consequently, ASSLBs with a LiNi0.83Co0.07Mn0.1O2 cathode containing LCCB-10 (CB/PEG mass ratio: 100/10) demonstrate a high areal capacity (2.53 mAh g–1/0.32 mA g–1) and remarkable rate capability (0.58 mAh g–1 at 1.4 mA g–1), with 88% capacity retention over 1000 cycles.

Stabilization of single crystal LiNi0.90Mn0.05Co0.05O2 via ZrO2 dual-functional coating enables superior performance for solid-state lithium battery

Chlorine-rich argyrodites with ultrafast Li-ion conductivities exhibits great potential as solid electrolytes for all-solid-state lithium batteries. However, the poor interfacial stability and slow ion dynamics between Li5.5PS4.5Cl1.5 (Cl1.5) and high nickel layered cathode hinder the achievement of superior battery performances. Here, the prepared ZrO2 coating film was found to perform two functions: enhancing the bulk and interfacial stability of single crystal LiNi0.90Mn0.05Co0.05O2 (NCM911) towards sulfide, and facilitating Li-ion transport rates across the interface. A Li2ZrO3 phase with fast Li-ion diffusion rate generates during cycling and further improve the layered-structure integrity of NCM911 and interfacial stability toward the Cl1.5 electrolyte, which are due to the reduction of lattice oxygen release from NCM911 and the isolation of direct contact between the two materials. As a result, these effects enable superior electrochemical performances for the ZrO2-coated NCM911 than the bare sample in Cl1.5-based all-solid-state lithium batteries at varying C-rates and different operating temperatures. It delivers high initial discharge capacities of 156.6 mAh g−1 at 2C and retains 86.0 % of its capacity after 1000 cycles at room temperature, and displays an initial discharge capacity of 172.6 mAh g−1 at 0.5C under 60 °C and 142.4 mAh g−1 at 0.1C under –20 °C, respectively. This dual-functional surface modification strategy provides guidelines to stabilize high-nickel cathode in sulfide-based all-solid-state lithium batteries.

Supplying active lithium to single-crystal Li(Ni0.90Co0.05Mn0.05)0.98Ta0.02O2 with Li2MnO3 coating served as cathode for Li-ion batteries

Ni-rich layered oxide with Ni molar content larger than 90% was regarded as an extremely promising candidate for cathode material applied in lithium-ion batteries owing to the significant discharging capacity and low cost. Nevertheless, rigorous cycling attenuation resulted from the crystal structure collapse and unstable particles interface deeply restrained the commercial application. In the work, LiNi0.90Co0.05Mn0.05O2 was modified by Ta5+ doping and Li2MnO3 covering, which was aimed to enhance the structure stability, defend the electrolyte attacking and promote Li+ migration during cycling. The material characterization demonstrated the cathodes after Ta5+ doping delivered the larger cell lattice parameters and higher cation ordering, which was helpful to improve the rate property and discharge capacity at low temperature. The Li2MnO3 layer was tightly adhered on the outside of LiNi0.90Co0.05Mn0.05O2, which could effectively relieve the electrolyte attacking and sustain the particle morphology integrity. As a result, 2 wt% Li2MnO3 coated Li(Ni0.90Co0.05Mn0.05)0.98Ta0.02O2 exhibited the outstanding discharge capacity of 150.2 mAh g−1 at 10.0 large current density and 140.6 mAh g−1 at −30 °C as well as the remarkable capacity retention of 93.1% after 300 cycles. Meanwhile, the pouch full batteries obtained by 2 wt% Li2MnO3 coated Li(Ni0.90Co0.05Mn0.05)0.98Ta0.02O2 also showed the more stable storage capability, cyclic property in comparison with bare LiNi0.90Co0.05Mn0.05O2.

High-performance single crystal Ni-rich cathode with regulated lattice and interface constructed by separated lithiation and crystallization calcination

Incorporating high valence dopants, such as W6+ and Mo6+ has been verified to be effective for tuning the microstructure and grain boundary of polycrystal Ni-rich cathode. However, the hindered consolidation of primary particles induced by dopants during lithiation calcination limits the utilization of those dopants to crystalize single-crystal Ni-rich cathodes with stabilized lattice and surface. Herein, high performance single crystal LiNi0.84Co0.11Mn0.05O2 cathode with Al3+ and W6+ regulated lattice and boundary phase was construed based on commercial process with two-step calcination process containing separated lithiation and crystallization. The introduction of appropriate amount of Al3+ in the first lithiation calcination of 6 h endows the bulk of crystalline with enhanced lattice stability, while the incorporation of W6+ with stoichiometrical LiOH in the secondary crystallization calcination of 6 h renders uniformly distributed surface layer without hampering the growth of single-crystal. With the Al3+ doped bulk lattice, W6+ doped subsurface region and hetero-epitaxially grown Li2WO4, the cathode infused by two-step calcination exhibits high discharge capacity, rate performance, and cycling stability. Specifically, the modified LiNi0.84Co0.11Mn0.05O2 exhibits exceptional capacity retention, maintaining 88.98% of its initial capacity after 200 cycles at a rate of 1 C within a voltage window of 2.7–4.3 V at a temperature of 25 °C in half-cell. This performance is markedly superior to the capacity retention of 72.96% observed for pristine cathode. Even when subjected to a stringent test after 200 cycles at the same rate, the modified cathode sustains an impressive capacity retention of 82.41% at an elevated cut-off voltage of 4.5 V and a temperature of 30 °C.

An Efficient and Eco-Friendly Recycling Route of Valuable Metals from Spent Ternary Li-Ion Batteries: Kinetics Evaluation of Chlorination Processes and Regeneration of LiNi0.8Co0.1Mn0.1O2 Cathode Materials.

The recycling of spent Li-ion batteries is urgent, and the effective recovery of valuable metals from spent cathode material is an economic and eco-friendly approach. In this study, Ni, Cu, Co, and Mn were extracted synchronously from spent LiNixCoyMn1-x-yO2 by chlorination and the complexation reaction of ammonium chloride at low temperatures. The kinetics of the chlorination process was investigated by nonisothermal thermal analysis to determine the rate equation of metal conversion, and the apparent activation energies were calculated to be 99.96 kJ·mol-1 for lithium and 146.70 kJ·mol-1 for nickel, cobalt, and manganese, respectively. The separation of valuable metals from polymetallic leaching solution and the regeneration of cathode materials were further investigated to promote the industrialization of the process. The recoveries of Ni, Co, Mn, and Li can reach 97.75, 99.99, 99.99, and 92.23%, respectively. The prepared LiNi0.8Co0.1Mn0.1O2 precursor is a multilayer spherical particle formed by stacking primary hexagonal nanosheets along the (010) crystal axis, the formation mechanism of which was discussed. The effect of temperature, time, and mixed lithium ratio on the performance of single crystal LiNi0.8Co0.1Mn0.1O2 cathode in the synthesis process was investigated to determine the optimum conditions. Compared with commercial materials, the prepared single crystal LiNi0.8Co0.1Mn0.1O2 cathode has a more regular crystal structure and higher initial discharge capacity (215.9 mAh·g-1 at 0.1 C).

Dual-coated single-crystal LiNi0.6Co0.2Mn0.2O2 as high-performance cathode materials for lithium-ion batteries

Dual-coated single-crystal LiNi0.6Co0.2Mn0.2O2 as high-performance cathode materials for lithium-ion batteries

Unveiling the Stability Mechanism of Oriented Ni-Rich Layered Oxides.

Single-crystal and polycrystalline structures are the two main structural forms of the Ni-rich layered cathode for lithium-ion batteries. The structural difference is closely related to the electrochemical performance and thermal stability, but its internal mechanism is unclear and is worthy of further exploration. In this study, both polycrystalline and single-crystal LiNi0.83Co0.12Mn0.05O2 cathodes were prepared by adjusting the calcination temperature and mechanical post-treatment, respectively. Systematic comparisons were made to assess the effects of different grain structures on the electrochemical performance and thermal stability. The study revealed the superior thermal stability of monocrystalline cathodes, attributing it to oxygen vacancies and phase transitions. From the perspective of grain boundaries, it was demonstrated that the diffusion of oxygen vacancies and the reduction of Ni in polycrystalline cathodes exhibit anisotropy. This research elucidates the origins of the superior thermal stability of monocrystalline cathodes in lithium-ion batteries, providing valuable insights into battery material design.

Achieving thermodynamic stability of single-crystal ultrahigh-nickel cathodes via an alcohol-assisted mechanical fusion

Elevating the operating voltage is an effective approach to improve the reversible capacity of ultra-high nickel layered oxide cathode LiNixCoyMnzO2 (NCM, x ≥ 0.8) and solve the “range anxiety” confusion of electric vehicles. However, the undesirable surface reconstruction induced by the high cut-off voltage has a fatal impact on the thermodynamic stability of the material, inevitably leading to fast capacity degradation. Herein, a mechanical fusion aided by alcohol is suggested to create a stable olivine structure for the single-crystal (SC) ultrahigh-nickel cathode LiNi0.92Co0.04Mn0.04O2. The addition of nanoparticles effectively bridges the void of SC-NCM, builds an ideal particle grading, and significantly raises the cost efficiency, as well as promotes the cycling stability and safety of the full cell. Remarkably, the layered/olivine mixture forms a perfect shield by lowering the surface area between the NCM cathode and electrolyte, hence mitigating side reactions and contributing to an incredibly thin and stable cathode/electrolyte interface. Furthermore, the thermodynamic stability of highly delithiated NCM is improved, as both the particle cracks and structural degradation are simultaneously postponed. Consequently, the maximum temperature of the single-crystal LiNi0.92Co0.04Mn0.04O2@LiFePO4‖graphite pouch full cell is dramatically reduced from 599.4 to 351.4 °C, and the full cell achieves 88.2% capacity retention after 800 cycles, demonstrating excellent thermal stability and cycling stability. This facile strategy provides a feasible technical reference for further exploiting the ultrahigh-capacity, high-safety, and long-life Ni-rich cathode for commercial application of lithium-ion batteries (LIBs).

Na+ orientates Jahn-Teller effect to tune Li+ diffusion pathway and kinetics for Single-Crystal Ni-rich LiNixCoyMn1-x-yO2 cathode materials

Single-crystallization is an effective strategy for enhancing both capacity and stability of Ni-rich LiNi1-x-yCoxMnyO2 (NCM) cathode materials, especially at high cut-off voltages. However, the kinetics limitation of solid-phase Li+ diffusion is a major concern because of the long diffusion path in large single-crystal particles. To address this issue, we synthesize a Na-doped single-crystal LiNi0.82Co0.125Mn0.055O2 (NCM-Na) cathode material by a facile mixed-molten-salt sintering process. Na+ is revealed to be uniformly doped at the Li+ lattice sites within the entire single-crystal particles. This Na+ doping effectively enhances the dynamics of Li+ transport in the layered oxide phases. The NCM-Na material with 2 at.% Na doping shows a Li+ diffusion coefficient up to more than 8 times higher than pristine NCM. In-situ X-ray diffraction and finite element analysis demonstrate significantly facilitated H1-H2-H3 phase transition in NCM-Na materials, compared with the severe phase separation phenomenon in NCM counterpart, hoisting their rate capacity and structure stability. Thus, the NCM-Na material achieves a superior reversible capacity of 177.7 mAh/g at 5C, and a capacity retention of 94.4 % after 100 cycles at 0.5C at a high cut-off voltage of 4.5 V. By density function theory calculations, we reveal that Na+ doping can selectively stabilize the surrounding Li+ at the second farthest hexagonal vertexes by tuning the orientation of the Jahn-Teller effect of Ni3+. These Li+ ions frame a high-speed pathway for preferential Li+ diffusion, which promotes the Li+ diffusion kinetics even in highly delithiated states. Our findings provide insights into the Na+ doping mechanism and present a low-cost, highly efficient, and scalable method to enhance the performance of single-crystal Ni-rich NCM materials.

Surface-to-bulk engineering with high-valence W6+ enabling stabilized single-crystal LiNi0.9Co0.05Mn0.05O2 cathode

Single-crystal Nickel-rich layered oxides has been recognized as one of the promising cathodes for next-generation lithium batteries on account of their high capacity, while its practical application was hindered by structural instability and slow Li+ transfer kinetics. Herein, a surface-to-bulk engineered single-crystal LiNi0.9Co0.05Mn0.05O2 (Ni90) cathode, which features W-doped bulk and Li2WO4 surface layer, was successfully achieved by a one-step high-valence W6+ modification. The as-obtained W-modified Ni90 delivers excellent cycling stability (89.8% capacity retention after 300 cycles at 0.5 C) and rate capability. The enhanced electrochemical performance was ascribed to the doped-W induced stabilized lattice oxygen, reduced Li+/Ni2+ mixing and inhibited H2-H3 phase transition in the bulk, and Li2WO4 layer generated stabilized cathode/electrolyte interface. In addition, the thinner LiF-rich cathode electrolyte interphase (CEI) on surface and smaller grain size for W-modified Ni90 benefit to its Li+ diffusion dynamics. The effect of high-valence W6+ on single-crystal Ni-rich cathode was firstly revealed in detail, which deepens the understanding of electrochemical behavior of Ni-rich cathode with high-valence cations modification, and provides clues for design of high-performance layered cathodes.

Mitigating kinetic hindrance of single-crystal Ni-rich cathodes through morphology modulation, nickel reduction, and lithium vacancy generation achieved by terbium doping

Single crystallization has proven to be effective in enhancing the capacity and stability of Ni-rich LiNi1−x−yCoxMnyO2 (SNCM) cathode materials, particularly at high cut-off voltages. Nevertheless, the synthesis of high-quality single-crystal particles remains challenging because of severe particle agglomeration and irregular morphologies. Moreover, the limited kinetics of solid-phase Li+ diffusion pose a significant concern because of the extended diffusion path in large single-crystal particles. To address these challenges, we developed a Tb-doped single-crystal LiNi0.83Co0.11Mn0.06O2 (SNCM-Tb) cathode material using a straightforward mixed molten salt sintering process. The Tb-doped Ni-rich single crystals presented a quasi-spherical morphology, which is markedly different from those reported in previous studies. Tb4+ doping significantly enhanced the dynamic transport of Li+ ions in the layered oxide phase by reducing the Ni valence state and creating Li vacancies. A SNCM-Tb material with 1 at% Tb doping shows a Li+ diffusion coefficient up to more than 9 times higher than pristine SNCM in the non-diluted state. In situ X-ray diffraction analysis demonstrated a significantly facilitated H1-H2-H3 phase transition in the SNCM-Tb materials, thereby enhancing their rate capacity and structural stability. SNCM-Tb exhibited a reversible capacity of 186.9 mA h g−1 at 5 C, retaining 94.6% capacity after 100 cycles at 0.5 C under a 4.5 V cut-off. Our study elucidates the Tb4+ doping mechanisms and proposes a scalable method for enhancing the performance of single-crystal Ni-rich NCM materials.

Insights into the effects of coating and single crystallization on the rate performance and cycle life of LiNi0.9Mn0.1O2 cathode

Coating and single crystal are two common strategies for cobalt-free nickel-rich layered oxides to solve its poor rate performance and cycle stability. However, the action mechanism of different modification protocols to suppress the attenuation are unclear yet. Herein, the Li2MoO4 layer-coated polycrystalline LiNi0.9Mn0.1O2 (1.0 %-Mo + NM91) and single crystal LiNi0.9Mn0.1O2 (SC-NM91) are prepared to investigate this difference, respectively. By focusing on the interior of particles, the relationship between structure evolution and electrochemical behavior is systematically studied, and the intrinsic mechanism of coating/single-crystallization modifications on suppressing the attenuation is clarified. The results show that microcracks in LiNi0.9Mn0.1O2 (NM91) are the main culprit leading to the rate capability decay, and the coating can effectively prevent the radial diffusion of microcracks from the center to surface, inhibiting the generation of surface side reactions. Therefore, the coating has a more advantage in improving the rate performance at 5.0C, the discharge capacity of 1.0 %-Mo + NM91 (130.6 mAh/g) is 7.9 % higher than that of SC-NM91 (121.0 mAh/g). In contrast, the single-crystallization can effectively prevent the formation of intergranular cracks arising from the anisotropic stress in NM91, which causes the severe cycle degradation. Correspondingly, the grain boundary-free SC-NM91 shows superior cyclability. The capacity retention rate of SC-NM91 (80.8 %) at 0.2C after 100cycles is 6.3 % higher than that of 1.0 %-Mo + NM91 (74.5 %). This work concludes the effect difference of different modification methods on enhancing the electrochemical performance, which provides theoretical and technical guidance for the optimized and targeted modification design in the cobalt-free high nickel cathode materials.

Strengthening the interfacial stability of single-crystal LiNi0.88Co0.09Mn0.03O2 cathode with multiple-function surface modification

The instability in the structural integrity caused by interfacial issues is commonly regarded as the primary drawback of Ni-rich layered cathode materials (LiNixCoyMn1-x-yO2, where x ≥ 0.8), which must be addressed before their commercial application. Herein, a novel multiple-function surface modification strategy is proposed based on the single crystal structure to in-situ achieve the construction of a coating layer and surface doping with Ce element to enhance the structural stability of the LiNi0.88Co0.09Mn0.03O2 (NCM). Notably, the introduction of Ce-O bonding adjusts the local oxygen coordination to achieve a more stabilized structure of the oxygen framework, which inhibits the evolution of lattice oxygen and enhances conductivity. Additionally, by benefiting from the in-situ synthesized coating layer of LixCeO2, the occurrence of side reactions on the surface is effectively alleviated, resulting in a reduction in electrode polarization. Combined with comprehensive electrochemical tests, it is confirmed that the improved electrochemical performance originates from the reduction of the detrimental H2-H3 phase transition and enhanced conductivity. As expected, the modified material with 1 wt% content of Ce (NCM@Ce) exhibits a high initial discharge capacity of 196.3 mAh g−1 with a capacity retention of 79.7 % after 200 cycles, and its energy density reaches 574.3 Wh kg−1 after 200 cycles.

Improving storage performance and lattice oxygen stability of single crystal LiNi0.925Co0.03Mn0.045O2 by integrating utilization of surface residual lithium and lattice modulation

In lithium-ion batteries, Ni-rich single crystal cathode material (Ni > 90 %) is a promising cathode material, but it has not yet been put into commercial application due to defects such as structural degradation, air sensitivity and thermal instability. In this paper, the residual lithium compounds on the surface of high-nickel materials are not useless. Li3PO4 coated and Mg2+ doped single crystal cathode materials (SC-NCM-MP) were successfully prepared by precisely controlling the amount of MgHPO4 by titration and reacting with lithium compounds left on the surface of LiNi0.925Co0.03Mn0.045O2 (SC-NCM) cathode materials. The SC-NCM-MP samples exhibit better lattice oxygen stability, Li-ion mobility, storage performance and electrochemical performance, with a retention of 89.36 % after 100 cycles, which is much higher than 79.78 % of SC-NCM.

High voltage electrochemical performance of single crystal LiNi0.8Co0.1Mn0.1O2 cathode materials with Al-Mg dual doping

Single-crystal materials have high structural stability and low parasitic side reactions for nickel-rich cathodes due to the absence of grain boundaries. However, they suffer challenges such as the complex synthesis route, sluggish lithium-ion diffusion kinetics, and microcracking evolution at high voltage. Bulk co-doping of Al and Mg into the precursors is first employed by a co-precipitation method, and then the Al-Mg dual-doped single-crystal NCM811 cathode is successfully prepared using a straightforward one-step method to reduce production cost. The cycle retention of the corresponding optimized single-crystal material is notably increased by 24.36% compared to the commercial counterpart at 1 C and a high voltage of 4.5 V. Additionally, the discharge capacity at 0.1 C is improved by 4.64% compared to the commercial one with an appropriate annealing temperature and lithium salt ratio. Some advances in the synthesis approach and modification strategy for developing commercial single-crystal material are provided.

Al/Zr synergetic modification tailored low-cobalt single crystal LiNi0.72Co0.05Mn0.23O2 cathode for high-performance lithium-ion battery

Nickle (Ni)-rich layered oxides as promising candidate of high-capacity cathode materials have aroused extensive concern primarily regarding their higher specific capacity. However, the major hurdle of Ni-rich cathodes (Ni content ≥0.7) is their poor cycling stability, which often suffers from the release of oxygen, structural degradation and increased impedance during cycling, especially at high voltage or high temperature. Herein, we demonstrated a feasible solid phase method for easy industrialization based on the Al3+/Zr4+ co-doping in LiNi0.72Co0.05Mn0.23O2 (AXZY-NCM) single-crystal cathode. The optimized A0.5Z0.5-NCM single-crystal material exhibited greatly enhanced structural and thermal stability. XRD refinement results indicated that both Al3+ and Zr4+ were mainly located in transition metal (TM) sites, strengthening the layered structure through strong M-O bonds and inhibiting cation mixing. In-situ XRD revealed that the synergistic rivet effect of Al/Zr co-doping alleviates anisotropic lattice stress-strain during charge/discharge process. Accordingly, the A0.5Z0.5-NCM cathode can output a high initial capacity of 177.3 mAh g−1 at 1 C, and captured a more desirable capacity retention of 85.10 % than that of U-NCM (74.33 %) at 1 C over 200 cycles. Even at a high voltage of 4.5 V, its capacity retention can still reach 82.37 %, significantly surpassing the unmodified U-NCM (31.0 %). The above results demonstrated that well-designed dual doping is highly effective for strengthen structure stability and cycling performance of Ni-rich cathodes.

In Situ Fracture Behavior of Single Crystal LiNi0.8Mn0.1Co0.1O2 (NMC811)

AbstractSingle crystal particle morphologies have become highly desirable for next generation cathode materials, removing grain boundary fracture and thereby reducing the surface area exposed to electrolyte. The intrinsic mechanical behavior of single crystal layered oxides, however, is poorly understood. Here, faceted single crystal LiNi0.8Mn0.1Co0.1O2 (NMC811) particles are compressed in situ in a scanning electron microscope (SEM), to determine mechanical deformation mechanisms as a function of crystallographic orientation. In situ, the dynamical deformation sequence observed is initial cracking at the compression zone, followed by accelerated transparticle crack propagation and concurrent (0001) slip band formation. The greatest loads and contact pressure at fracture, non‐basal cracking, and activation of multiple basal slip systems in larger (>3 μm) particles, occur for compression normal to the (0001) layered structure. Loading on {012} preferentially activates basal fracture and slip at lower loads. Regardless of particle orientation, non‐basal slip systems are not observed, and non‐basal cracking and particle rotation occur during compression to compensate for this inability to activate dislocations in 3‐dimensions. Crystallographic dependent mechanical behaviour of single crystal NMC811 means that particle texture in cathodes should be monitored, and sources of localised surface stress in cathodes, e. g. particle‐to‐particle asperity contacts during electrode manufacture, should be minimised.