Crack-free single-crystal LiNi0.83Co0.10Mn0.07O2 as cycling/thermal stable cathode materials for high-voltage lithium-ion batteries

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.

Designing Reliable Cathode System for High-Performance Inorganic Solid-State Pouch Cells

All-solid-state batteries (ASSBs) based on inorganic solid electrolytes fascinate a large body of researchers in terms of overcoming the inferior energy density and safety issues of existing lithium-ion batteries. To date, the cathode designs in the ASSBs achieve remarkable achievements, adding the urgency of scaling up the battery system toward inorganic solid-state pouch cell configuration for the application market. Herein, the recent developments of cathode materials and the design considerations for their application in the pouch cell format are reviewed to straighten out the roadmap of ASSBs. Specifically, the intercalation compounds and the conversion materials with conversion chemistries are highlighted and discussed as two potentially valuable material types. This review focuses on the basic electrochemical mechanisms, mechanical contact issues, and sheet-type structure in inorganic solid-state pouch cells with corresponding perspectives, thus guiding the future research direction. Finally, the benchmarks for manufacturing inorganic solid-state pouch cells to meet practical high energy density targets are provided in this review for the development of commercially viable products.

Construction of Hierarchical Conductive Networks for LiNi0.8Mn0.1Co0.1O2 Cathode toward Stable Cycling at High Areal Mass Loadings

Realizing high-performance thick electrodes is considered as a practical strategy to promote the energy density of lithium-ion batteries. However, establishing effective transport pathways for both lithium-ions and electrons in a thick electrode is very challenging. This study develops a hierarchical conductive network structure for constructing high-performance NMC811 (LiNi0.8Mn0.1Co0.1O2) cathode toward stable cycling at high areal mass loadings. The hierarchical conductive networks are composed of a Li+/e- mixed conducting interface (lithium polyacrylate/hydroxyl-functionalized multiwalled carbon nanotubes) on NMC811 particles, and a segregated network of single-walled carbon nanotubes in the electrode, without any additional binders or carbon black. Such strategy endows the NMC811 cathode (up to 250 µm and 50 mg cm-2) with low porosity/tortuosity, ultrahigh Li+/e- conductivities and excellent mechanical property at low carbon nanotube content (1.8 wt%). It significantly improves the electrochemical reaction homogeneity along the electrode depth, meanwhile effectively inhibits the side reactions at the electrode/electrolyte interface and cracks in the NMC particles during cycling. This work emphasizes the crucial role of the electronic/ionic cooperative transportation in the performance deterioration of thick cathodes, and provide guidance for architecture optimization and performance improvement of thick electrodes toward practical applications, not just for the NMC811 cathode.

Molten salt synthesis of disordered spinel CoFe2O4 with improved electrochemical performance for sodium-ion batteries

Sodium-ion (Na-ion) batteries are currently being investigated as an attractive substitute for lithium-ion (Li-ion) batteries in large energy storage systems because of the more abundant and less expensive supply of Na than Li. However, the reversible capacity of Na-ions is limited because Na possesses a large ionic radius and has a higher standard electrode potential than that of Li, making it challenging to obtain electrode materials that are capable of storing large quantities of Na-ions. This study investigates the potential of CoFe2O4 synthesised via the molten salt method as an anode for Na-ion batteries. The obtained phase structure, morphology and charge and discharge properties of CoFe2O4 are thoroughly assessed. The synthesised CoFe2O4 has an octahedron morphology, with a particle size in the range of 1.1-3.6 μm and a crystallite size of ∼26 nm. Moreover, the CoFe2O4 (M800) electrodes can deliver a high discharge capacity of 839 mA h g-1 in the first cycle at a current density of 0.1 A g-1, reasonable cyclability of 98 mA h g-1 after 100 cycles and coulombic efficiency of ∼99%. The improved electrochemical performances of CoFe2O4 can be due to Na-ion-pathway shortening, wherein the homogeneity and small size of CoFe2O4 particles may enhance the Na-ion transportation. Therefore, this simple synthetic approach using molten salt favours the Na-ion diffusion and electron transport to a great extent and maximises the utilisation of CoFe2O4 as a potential anode material for Na-ion batteries.

Outstanding Electrochemical Performance of Ni-Rich Concentration-Gradient Cathode Material LiNi0.9Co0.083Mn0.017O2 for Lithium-Ion Batteries

The full-concentrationgradient LiNi_0.9Co_0.083Mn_0.017O₂ (CG-LNCM), consisting of core Ni-rich LiNi_0.93Co_0.07O₂, transition zone LiNi_1-x-yCo_xMn_yO_2, and outmost shell LiNi_1/3Co_1/3Mn_1/3O₂ was prepared by a facile co-precipitation method and high-temperature calcination. CG-LNCM was then investigated with an X-ray diffractometer, ascanning electron microscope, a transmission electron microscope, and electrochemical measurements. The results demonstrate that CG-LNCM has a lower cation mixing of Li⁺ and Ni²⁺ and larger Li⁺ diffusion coefficients than concentration-constant LiNi_0.9Co_0.083Mn_0.017O₂ (CC-LNCM). CG-LNCM presents a higher capacity and a better rate of capability and cyclability than CC-LNCM. CG-LNCM and CC-LNCM show initial discharge capacities of 221.2 and 212.5 mAh g^-1 at 0.2C (40 mA g^-1) with corresponding residual discharge capacities of 177.3 and 156.1 mAh g^-1 after 80 cycles, respectively. Even at high current rates of 2C and 5C, CG-LNCM exhibits high discharge capacities of 165.1 and 149.1 mAh g^-1 after 100 cycles, respectively, while the residual discharge capacities of CC-LNCM are as low as 148.8 and 117.9 mAh g^-1 at 2C and 5C after 100 cycles, respectively. The significantly improved electrochemical performance of CG-LNCM is attributed to its concentration-gradient microstructure and the composition distribution of concentration-gradient LiNi_0.9Co_0.083Mn_0.017O₂. The special concentration-gradient design and the facile synthesis are favorable for massive manufacturing of high-performance Ni-rich ternary cathode materials for lithium-ion batteries.

Cathode Electrolyte Interphase-Forming Additive for Improving Cycling Performance and Thermal Stability of Ni-Rich LiNixCoyMn1-x-yO2 Cathode Materials

High-capacity Ni-rich LiNi_xCo_yMn_1-x-yO₂ (NCM) has been investigated as a promising cathode active material for improving the energy density of lithium-ion batteries (LIBs); however, its practical application is limited by its structural instability and low thermal stability. In this study, we synthesized tetrakis(methacryloyloxyethyl)pyrophosphate (TMAEPPi) as a cathode electrolyte interphase (CEI) additive to enhance the cycling characteristics and thermal stability of the LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) material. TMAEPPi was oxidized to form a uniform Li⁺-ion-conductive CEI on the cathode surface during initial cycles. A lithium-ion cell (graphite/NCM811) employing a liquid electrolyte containing 0.5 wt % TMAEPPi exhibited superior capacity retention (82.2% after 300 cycles at a 1.0 C rate) and enhanced high-rate performance compared with the cell using a baseline liquid electrolyte. The TMAEPPi-derived CEI layer on NCM811 suppressed electrolyte decomposition and reduced the microcracking of the NCM811 particles. Our results reveal that TMAEPPi is a promising additive for forming stable CEIs and thereby improving the cycling performance and thermal stability of LIBs employing high-capacity NCM cathode materials.

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-Crystalline Cathodes for Advanced Li-Ion Batteries: Progress and Challenges

Single-crystalline cathodes are the most promising candidates for high-energy-density lithium-ion batteries (LIBs). Compared to their polycrystalline counterparts, single-crystalline cathodes have advantages over liquid-electrolyte-based LIBs in terms of cycle life, structural stability, thermal stability, safety, and storage but also have a potential application in solid-state LIBs. In this review, the development history and recent progress of single-crystalline cathodes are reviewed, focusing on properties, synthesis, challenges, solutions, and characterization. Synthesis of single-crystalline cathodes usually involves preparing precursors and subsequent calcination, which are summarized in the details. In the following sections, the development issues of single-crystalline cathodes, including kinetic limitations, interfacial side reactions, safety issues, reversible planar gliding and micro-cracking, and particle size distribution and agglomeration, are systematically analyzed, followed by current solutions and characterization techniques. Finally, this review is concluded with proposed research thrusts for the future development of single-crystalline cathodes.

Effects of Co/Mn Content Variation on Structural and Electrochemical Properties of Single-Crystal Ni-Rich Layered Oxide Materials for Lithium Ion Batteries

The development of single-crystal nickel-rich layered LiNi_xCo_yMn_1-x-yO₂ materials (S-NCMs) represents the most significant progress for the electrification applications of nickel-rich ternary materials. There has been prior research on the important role of transition metal elements in agglomerated materials, supplemented by surface and internal lattice optimization to drive the performance improvements. However, studies on S-NCMs, especially on the role of transition metals (TM, i.e., Co and Mn), have not been reported. In this study, we synthesized four kinds of S-NCMs with different Co/Mn contents and studied their structural, electrochemical, kinetic, and thermodynamic properties with different Co/Mn contents. The results were as follows: (1) Electrochemically, Co was more effective than Mn at 25 °C at enhancing the intercalation/deintercalation kinetics, which resulted in an increased discharge capacity, an improved rate capability, and a reduced energy loss. (2) Thermodynamically, Mn was more effective at maintaining a higher thermal stability than Co, especially at a low cutoff voltage, but at a high cutoff voltage, the difference between the action of Co and Mn decreased. The main finding of this work was the enhanced structural stability provided by Co, which could be attributed to the following: (i) the absence of the H2/H3 phase transformation when Co exceeded 15%, which inhibited the irreversible phase transformation and reduced the volume strain, and (ii) the lower degrees of decrease in the cell parameters a and c with higher contents of Co, which contributed to a low cracking degree along the (003) crystal plane. The current work provides an important reference for the single-crystallization strategy of nickel-rich materials.

Layered Cathode Materials: Precursors, Synthesis, Microstructure, Electrochemical Properties, and Battery Performance

The exploitation of clean energy promotes the exploration of next-generation lithium-ion batteries (LIBs) with high energy-density, long life, high safety, and low cost. Ni-rich layered cathode materials are one of the most promising candidates for next-generation LIBs. Numerous studies focusing on the synthesis and modifications of the layered cathode materials are published every year. Many physical features of precursors, such as density, morphology, size distribution, and microstructure of primary particles pass to the resulting cathode materials, thus significantly affecting their electrochemical properties and battery performance. This review focuses on the recent advances in the controlled synthesis of hydroxide precursors and the growth of particles. The essential parameters in controlled coprecipitation are discussed in detail. Some innovative technologies for precursor modifications and for the synthesis of novel precursors are highlighted. In addition, future perspectives of the development of hydroxide precursors are presented.

Morphological Evolution and Solid-Electrolyte Interphase Formation on LiNi0.6Mn0.2Co0.2O2 Cathodes Using Highly Concentrated Ionic Liquid Electrolytes

Employing high-voltage Ni-rich cathodes in Li metal batteries (LMBs) requires stabilization of the electrode/electrolyte interfaces at both electrodes. A stable solid-electrolyte interphase (SEI) and suppression of active material pulverization remain the greatest challenges to achieving efficient long-term cycling. Herein, studies of NMC622 (1 mAh cm^-2) cathodes were performed using highly concentrated N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (C₃mpyrFSI) 50 mol % lithium bis(fluorosulfonyl)imide (LiFSI) ionic liquid electrolyte (ILE). The resulting SEI formed at the cathode enabled promising cycling performance (98.13% capacity retention after 100 cycles), and a low degree of ion mixing and lattice expansion was observed, even at an elevated temperature of 50 °C. Fitting of acquired impedance spectra indicated that the SEI resistivity (R_SEI) had a low and stable contribution to the internal resistivity of the system, whereas active material pulverization and secondary grain isolation significantly increased the charge transfer resistance (R_CT) throughout cycling.

Synergistic Dual-Salt Electrolyte for Safe and High-Voltage LiNi0.8Co0.1Mn0.1O2//Graphite Pouch Cells

Concerns about thermal safety and unresolved high-voltage stability have impeded the commercialization of high-energy lithium-ion batteries bearing LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathodes. Enhancing the cathode structure and optimizing the electrolyte formula have demonstrated significant potential in improving the high-voltage properties of batteries while simultaneously minimizing thermal hazards. The current study reports the development of a high-voltage lithium-ion battery that is both safe and reliable, using single-crystal NCM811 and a dual-salt electrolyte (DSE). After 200 cycles at high voltage (up to 4.5 V), the capacity retention of the battery with DSE was 98.80%, while that for the battery with a traditional electrolyte was merely 86.14%. Additionally, in comparison to the traditional electrolyte, the DSE could raise the tipping temperature of a battery's thermal runaway (TR) by 31.1 °C and lower the maximum failure temperature by 76.1 °C. Moreover, the DSE could effectively reduce the battery's TR heat release rate (by 23.08%) as well as eliminate concerns relating to fire hazards (no fire during TR). Based on material characterization, the LiDFOB and LiBF₄ salts were found to facilitate the in situ formation of an F- and B-rich cathode-electrolyte interphase, which aids in inhibiting oxygen and interfacial side reactions, thereby reducing the intensity of redox reactions within the battery. Therefore, the findings indicate that DSE is promising as a safe and high-voltage lithium-ion battery material.

Identifying surface degradation, mechanical failure, and thermal instability phenomena of high energy density Ni-rich NCM cathode materials for lithium-ion batteries: a review

Among the existing commercial cathodes, Ni-rich NCM are the most promising candidates for next-generation LIBs because of their high energy density, relatively good rate capability, and reasonable cycling performance. However, the surface degradation, mechanical failure and thermal instability of these materials are the major causes of cell performance decay and rapid capacity fading. This is a huge challenge to commercializing these materials widely for use in LIBs. In particular, the thermal instability of Ni-rich NCM cathode active materials is the main issue of LIBs safety hazards. Hence, this review will recapitulate the current progress in this research direction by including widely recognized research outputs and recent findings. Moreover, with an extensive collection of detailed mechanisms on atomic, molecular and micrometer scales, this review work can complement the previous failure, degradation and thermal instability studies of Ni-rich NMC. Finally, this review will summarize recent research focus and recommend future research directions for nickel-rich NCM cathodes.

High Nickel and No Cobalt─The Pursuit of Next-Generation Layered Oxide Cathodes

The prosperity of the electric vehicle industry is driving the research and development of lithium-ion batteries. As one of the core components in the entire battery system, cathode materials are currently facing major challenges in pushing a higher capacity up to the materials' theoretical limits and transitioning away from unaffordable metals. The search for next-generation cathode materials has shifted to high-nickel and cobalt-free cathodes to meet these requirements. In this review, we distinctly point out the shortcomings of cobalt in stabilizing layered structures and systematically summarize the recent efforts to eliminate cobalt and achieve higher nickel content in layered cathode materials. Finally, a reasonable prospect is put forward for further development of layered cathode materials and other promising candidates, which is likely to spur a wave of efforts toward developing high-performance and low-cost Li-ion batteries.

Synthesis Method and Thermodynamic Characteristics of Anode Material Li3FeN2 for Application in Lithium-Ion Batteries

Li₃FeN₂ material was synthesized by the two-step solid-state method from Li₃N (adiabatic camera) and FeN₂ (tube furnace) powders. Phase investigation of Li₃N, FeN₂, and Li₃FeN₂ was carried out. The discharge capacity of Li₃FeN₂ is 343 mAh g^-1, which is about 44.7% of the theoretic capacity. The ternary nitride Li₃FeN₂ molar heat capacity is calculated using the formula C_p,m = 77.831 + 0.130 × T - 6289 × T^-2, (T is absolute temperature, temperature range is 298-900 K, pressure is constant). The thermodynamic characteristics of Li₃FeN₂ have the following values: entropy S⁰₂₉₈ = 116.2 J mol^-1 K^-1, molar enthalpy of dissolution Δ_dH_LFN = -206.537 ± 2.8 kJ mol^-1, the standard enthalpy of formation Δ_fH⁰ = -291.331 ± 5.7 kJ mol^-1, entropy S⁰₂₉₈ = 113.2 J mol^-1 K^-1 (Neumann-Kopp rule) and 116.2 J mol^-1 K^-1 (W. Herz rule), the standard Gibbs free energy of formation Δ_fG⁰₂₉₈ = -276.7 kJ mol^-1.

Spontaneous Strain Buffer Enables Superior Cycling Stability in Single-Crystal Nickel-Rich NCM Cathode

The capacity degredation in layered Ni-rich LiNi_xCo_yMn_zO₂ (x ≥ 0.8) cathode largely originated from drastic surface reactions and intergranular cracks in polycrystalline particles. Herein, we report a highly stable single-crystal LiNi_0.83Co_0.12Mn_0.05O₂ cathode material, which can deliver a high specific capacity (∼209 mAh g^-1 at 0.1 C, 2.8-4.3 V) and meanwhile display excellent cycling stability (>96% retention for 100 cycles and >93% for 200 cycles). By a combination of in situ X-ray diffraction and in situ pair distribution function analysis, an intermediate monoclinic distortion and irregular H3 stack are revealed in the single crystals upon charging-discharging processes. These structural changes might be driven by unique Li-intercalation kinetics in single crystals, which enables an additional strain buffer to reduce the cracks and thereby ensure the high cycling stability.

Understanding the enhancement effect of boron doping on the electrochemical performance of single-crystalline Ni-rich cathode materials

Ni-rich layered oxides are considered as promising cathode materials for Li-ion batteries (LIBs) due to their satisfying theoretical specific capacity and reasonable cost. However, poor cycling stability caused by structural collapse and interfacial instability of the Ni-rich cathode material limits the further applications of commercialization. Herein, a series of B-doped single-crystal LiNi_0.83Co_0.05Mn_0.12O₂ (NCM) are designed and fabricated, aiming to improve the structural stability and enlarge the Li⁺-ions diffusion paths simultaneously. It reveals that B-doping at TM layers will facilitate the formation of stronger B-O covalent bonds and expand the layered distance, significantly enhancing the thermodynamics and kinetic of NCM electrode. With the synergistic effect of single-crystalline architecture and appropriate B-doping, it can effectively alleviate the occurrence of internal strain with structural degradation and boost the intrinsic rate capability synchronously. As anticipated, the 0.6 mol % B-doped NCM electrode exhibits enhanced rate property and superior cycle stability, even at the harsh condition of high-temperature and elevated cut-off voltage. Remarkably, when tested in pouch-type full-cell, it maintains high reversible capacity with superior capacity retention of 91.35% over 500 cycles with only 0.0173% decay per cycle. This research illustrates the feasibility of B-doping and single-crystalline architecture to improve the electrochemical performance, which is beneficial to understand the enhancement effect and provides the design strategy for the commercialization progress of Ni-rich cathode materials.

Recent Advances on Materials for Lithium-Ion Batteries

Environmental issues related to energy consumption are mainly associated with the strong dependence on fossil fuels. To solve these issues, renewable energy sources systems have been developed as well as advanced energy storage systems. Batteries are the main storage system related to mobility, and they are applied in devices such as laptops, cell phones, and electric vehicles. Lithium-ion batteries (LIBs) are the most used battery system based on their high specific capacity, long cycle life, and no memory effects. This rapidly evolving field urges for a systematic comparative compilation of the most recent developments on battery technology in order to keep up with the growing number of materials, strategies, and battery performance data, allowing the design of future developments in the field. Thus, this review focuses on the different materials recently developed for the different battery components—anode, cathode, and separator/electrolyte—in order to further improve LIB systems. Moreover, solid polymer electrolytes (SPE) for LIBs are also highlighted. Together with the study of new advanced materials, materials modification by doping or synthesis, the combination of different materials, fillers addition, size manipulation, or the use of high ionic conductor materials are also presented as effective methods to enhance the electrochemical properties of LIBs. Finally, it is also shown that the development of advanced materials is not only focused on improving efficiency but also on the application of more environmentally friendly materials.

Micron-Sized Monodisperse Particle LiNi0.6Co0.2Mn0.2O2 Derived by Oxalate Solvothermal Process Combined with Calcination as Cathode Material for Lithium-Ion Batteries

Ni-rich cathode LiNi_xCo_yMn_1-x-yO₂ (NCM, x ≥ 0.5) materials are promising cathodes for lithium-ion batteries due to their high energy density and low cost. However, several issues, such as their complex preparation and electrochemical instability have hindered their commercial application. Herein, a simple solvothermal method combined with calcination was employed to synthesize LiNi_0.6Co_0.2Mn_0.2O₂ with micron-sized monodisperse particles, and the influence of the sintering temperature on the structures, morphologies, and electrochemical properties was investigated. The material sintered at 800 °C formed micron-sized particles with monodisperse characteristics, and a well-order layered structure. When charged–discharged in the voltage range of 2.8–4.3 V, it delivered an initial discharge capacity of 175.5 mAh g⁻¹ with a Coulombic efficiency of 80.3% at 0.1 C, and a superior discharge capacity of 135.4 mAh g⁻¹ with a capacity retention of 84.4% after 100 cycles at 1 C. The reliable electrochemical performance is probably attributable to the micron-sized monodisperse particles, which ensured stable crystal structure and fewer side reactions. This work is expected to provide a facile approach to preparing monodisperse particles of different scales, and improve the performance of Ni-rich NCM or other cathode materials for lithium-ion batteries.

Enhanced Cycle Life and Rate Capability of Single-Crystal, Ni-Rich LiNi0.9Co0.05Mn0.05O2 Enabled by 1,2,4-1H-Triazole Additive

Ternary LiNi_xCo_yMn_zO₂ oxides with extremely high nickel (Ni) contents (x ≥ 0.9) are promising cathode candidates developed for higher-energy-density lithium-ion batteries, with an aim to relieve mileage anxiety. However, the structural and interfacial instability still restrict their application in electric vehicles. In this work, a novel electrolyte additive 1,2,4-1H-Triazole (HTZ) is introduced to improve the interfacial stability of LiNi_0.9Co_0.05Mn_0.05O₂ (NCM90), promoting cycle life both at 30 °C and a harsh condition of 60 °C, as well as rate capability. The NCM90||Li cells with 0.3% HTZ-added electrolyte retain 86.6% of their original capacity after 150 cycles at 1C and 30 °C, well exceeding 74.8% obtained with the baseline electrolyte. It is revealed that the additive HTZ could inhibit the thermal decomposition of LiPF₆ salt and suppress the generation of HF acidic species. More importantly, additive HTZ is preferentially oxidized to construct a compact and dense cathode electrolyte interphase (CEI) layer, which is beneficial for stabilizing the electrode/electrolyte interface and suppressing unwanted side reactions.

Intelligent phase-transition MnO2 single-crystal shell enabling a high-capacity Li-rich layered cathode in Li-ion batteries

Layered, Li-rich Mn-based oxides (LLMOs) are the most promising next-generation, high-energy batteries due to their relatively high specific capacities and high voltages. However, the practical application of LLMO cathodes is limited by low initial coulombic efficiencies (CEs) and poor cycling performance. Herein, we used the reaction of KMnO₄ and MnSO₄ under hydrothermal conditions to grow a nano-SCMO shell on the LLMO material surface (SCMO@LLMO). The unique particle/sheet compound structure of the SCMO shell is beneficial to the electrochemical reaction. SCMO has good Li storage characteristics and excellent surface structure stability in the single-crystal phase which further improves the reversible capacity, CE, and cyclic stability of the LLMO cathode. Therefore, the optimal coated sample (feedstock: 2 M KMnO₄, SCMO@LLMO-2.0) exhibits a good initial discharge capacity (238.2 mA h g⁻¹ at 1C and 173.8 mA h g⁻¹ at 5C), initial CE (89.6% at 1C and 86.5% at 5C), and cycling performance (capacity retention of 84.67% at 1C and 62.72% at 5C after 200 cycles). This work adopts a hydrothermal method to synthesize a nano-single crystal composite material, laying a foundation for the preparation of the SCMO@LLMO cathodes for LLMO primary battery cathodes with high electrochemical performance.

A MnO₂ single-crystal shell is synthesized on the surface of Li-rich Mn-based materials, enabling high-capacity Li-rich layered cathode in Li-ion batteries.