Air- and Moisture Robust Surface Modification for Ni-Rich Layered Cathode Materials for Li-Ion Batteries

The mainstream of high-energy cathode development is focused on increasing the Ni-ratio in layered structured cathode materials. The increment of the Ni portion in the layered cathode material escalates not only the deliverable capacity but also the structural degradation. High-Ni layered cathodes are highly vulnerable to exposure to air that contains CO₂ and H₂O, forming problematic residual lithium compounds at the surface. In this work, a novel air- and moisture robust surface modification is reported for LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) via the sol-gel coating method that selectively coats the internal surface area of the polycrystalline morphology secondary particles. Bare-, Li₂SnO₃-coated and LiCoO₂-coated NCM811 are exposed to different ambient environments (air, hot-air, and moisture-air) to systematically investigate the correlation between the internal/external coating morphology and performance degradations. The LiCoO₂-coated NCM811s exhibit high-capacity retention after exposure to all environments, due to the internal surface coating that prevents the penetration of harmful compounds into the polycrystalline NCM811. On the other hand, the Li₂SnO₃-coated NCM811s exposed to the ambient environments show gradual capacity fading, implying the occurrence of internal degradation. This paper highlights the impact of the internal degradation of polycrystalline NCM811 after environmental exposure and the correct coating mechanisms required to successfully prevent it.     

Microstructure-optimized concentration-gradient NCM cathode for long-life Li-ion batteries

Herein, a comprehensive investigation of the effect of calcination temperature on the physicochemical properties of full-concentration-gradient Li[Ni_0.78Co_0.10Mn_0.12]O₂ (FCG NCM78) and the electrochemical performance of FCG NCM78 cathodes was conducted. The electrochemical performance of the FCG NCM78 cathode was significantly influenced by the physical properties of FCG NCM78, such as crystallinity, compositional gradient, and morphology. The crystallinity of FCG NCM78 increased with increasing calcination temperature; however, the compositional gradient and radial alignment of rod-shaped primary particles increasingly disappeared at calcination temperatures exceeding the optimal calcination temperature. FCG NCM78 calcined at the optimal calcination temperature retained the morphological texture of its precursor and demonstrated high crystallinity; the resulting cathode exhibited remarkable cycling stability, thereby retaining 86.3% of its initial capacity after 4000 cycles, and superior rate capability due to the availability of nearly straight diffusion paths for Li-ion transport across adjacent primary particles. In contrast, excessively coarsened FCG NCM78 cathode particles, which are obtained at high calcination temperatures, develop permanent microcracks during cycling, thereby facilitating severe structural damage of the cathode material by parasitic surface reactions and the rapid deterioration of the solid electrolyte interphase layer on the graphite anode surface due to the crossover of dissolved transition-metal ions. Therefore, for superior electrochemical performance, the physicochemical properties of FCG cathode materials should be carefully optimized by controlling the calcination process.     

Facile synthesis and electrochemical properties of layered Li[Ni<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>]O<Subscript>2</Subscript> as cathode materials for lithium-ion batteries

A layered oxide Li[Ni_1/3Mn_1/3Co_1/3]O₂ was synthesized by an oxalate co-precipitation method. The morphology, structural and composition of the as-papered samples synthesized at different calcination temperatures were investigated. The results indicate that calcination temperature of the sample at 850°C can improve the integrity of structural significantly. The effect of calcination temperature varying from 750°C to 950°C on the electrochemical performance of Li[Ni_1/3Mn_1/3Co_1/3]O₂, cathode material of lithiumion batteries, has been investigated. The results show that Li[Ni_1/3Mn_1/3Co_1/3]O₂ calcined at 850°C possesses a higher capacity retention and better rate capability than other samples. The reversible capacity is up to 178.6 mA?h?g^-1, and the discharge capacity still remains 176.3 mA?h?g^-1 after 30 cycles. Moreover, our strategy provides a simple and highly versatile route in fabricating cathode materials for lithium-ion batteries.     

A Facile Strategy to Construct Silver‐Modified,ZnO‐Incorporated and Carbon‐Coated Silicon/Porous‐Carbon Nanofibers with Enhanced Lithium Storage

For Si anode materials used for lithium ion batteries (LIBs), developing an effective solution to overcome their drawbacks of large volume change and poor electronic conductivity is highly desirable. Here, the composites of ZnO‐incorporated and carbon‐coated silicon/porous‐carbon nanofibers (ZnO‐Si@C‐PCNFs) are designed and synthesized via a traditional electrospinning method. The prepared ZnO‐Si@C‐PCNFs can obviously overcome these two drawbacks and provide excellent LIB performance with excellent rate capability and stable long cycling life of 1000 cycles with reversible capacity of 1050 mA h g^?1 at 800 mA g^?1. Meanwhile, anodes of ZnO‐Si@C‐PCNFs attached with Ag particles display enhanced LIB performance, maintaining an average capacity of 920 mA h g^?1 at a large current of 1800 mA g^?1 even for 1000 cycles with negligible capacity loss and excellent reversibility. In addition, the assembling method with important practical significance for a simple pouch full cell is designed and used to evaluate the active materials. The Ag/ZnO‐Si@C‐PCNFs are prelithiated and assembled in full cells using LiNi_0.5Co_0.2Mn_0.3O₂(NCM523) as cathodes, exhibiting higher energy density (230 W h kg^?1) of 18% than that of 195 W h kg^?1 for commercial graphite//NCM523 full pouch cells. Importantly, the comprehensive mechanisms of enhanced electrochemical kinetics originating from ZnO‐incorporation and Ag‐attachment are revealed in detail.     

Facile preparation of core@shell and concentration-gradient spinel particles for Li-ion battery cathode materials

Abstract

Core@shell and concentration-gradient particles have attracted much attention as improved cathodes for Li-ion batteries (LIBs). However, most of their preparation routes have employed a precisely-controlled co-precipitation method. Here, we report a facile preparation route of core@shell and concentration-gradient spinel particles by dry powder processing. The core@shell particles composed of the MnO₂ core and the Li(Ni,Mn)₂O₄ spinel shell are prepared by mechanical treatment using an attrition-type mill, whereas the concentration-gradient spinel particles with an average composition of LiNi_0.32Mn_1.68O₄ are produced by calcination of their core@shell particles as a precursor. The concentration-gradient LiNi_0.32Mn_1.68O₄ spinel cathode exhibits the high discharge capacity of 135.3 mA h g^?1, the wide-range plateau at a high voltage of 4.7 V and the cyclability with a capacity retention of 99.4% after 20 cycles. Thus, the facile preparation route of the core@shell and concentration-gradient particles may provide a new opportunity for the discovery and investigation of functional materials as well as for the cathode materials for LIBs.     

Nanoscale Borate Coating Network Stabilized Iron Oxide Anode for High-Energy-Density Bipolar Lithium-Ion Batteries

High-capacity metal oxides based on non-toxic earth-abundant elements offer unique opportunities as advanced anodes for lithium-ion batteries (LIBs). But they often suffer from large volumetric expansion, particle pulverization, extensive side reactions, and fast degradations during cycling. Here, an easy synthesis method is reported to construct amorphous borate coating network, which stabilizes conversion-type iron oxide anode for the high-energy-density semi-solid-state bipolar LIBs. The nano-borate coated iron oxide anode has high tap density (1.6 g cm⁻³), high capacity (710 mAh g⁻¹ between 0.5 – 3.0 V, vs Li/Li⁺), good rate performance (200 mAh g⁻¹ at 50 C), and excellent cycling stability (≈100% capacity resention over 1,000 cycles at 5 A g⁻¹). When paired with high-voltage cathode LiCoO₂, it enables Cu current collector-free pouch-type classic and bipolar full cells with high voltage (7.6 V with two stack layers), achieving high energy density (≈350 Wh kg⁻¹), outstanding power density (≈6,700 W kg⁻¹), and extended cycle life (75% capacity retention after 2,000 cycles at 2 C), superior to the state-of-the-art high-power LIBs using Li₄Ti₅O₁₂ anode. The design and methodology of the nanoscale polyanion-like coating can be applied to other metal oxides electrode materials, as well as other electrochemical materials and devices.     

A Molecularly Engineered Cathode Lithium Compensation Agent for High Energy Density Batteries

Prelithiating cathode is considered as one of the most promising lithium compensation strategies for practical high energy density batteries. Whereas most of reported cathode lithium compensation agents are deficient owing to their poor air-stability, residual insulating solid, or formidable Li-extracting barrier. Here, this work proposes molecularly engineered 4-Fluoro-1,2-dihydroxybenzene Li salt (LiDF) with high specific capacity (382.7 mAh g⁻¹) and appropriate delithiation potential (3.6–4.2 V) as an air-stable cathode Li compensation agent. More importantly, the charged residue 4-Fluoro-1,2-benzoquinone (BQF) can synergistically work as an electrode/electrolyte interface forming additive to build uniform and robust LiF-riched cathode/anode electrolyte interfaces (CEI/SEI). Consequently, less Li loss and retrained electrolyte decomposition are achieved. With 2 wt% 4-Fluoro-1,2-dihydroxybenzene Li salt initially blended within the cathode, 1.3 Ah pouch cells with NCM (Ni92) cathode and SiO/C (550 mAh g⁻¹) anode can keep 91% capacity retention after 350 cycles at 1 C rate. Moreover, the anode free of NCM622+LiDF||Cu cell achieves 78% capacity retention after 100 cycles with the addition of 15 wt% LiDF. This work provides a feasible sight for the rational designing Li compensation agent at molecular level to realize high energy density batteries.     

Lithium Foam for Deep Cycling Lithium Metal Batteries

Li metal anode has been recognized as the most promising anode for its high theoretical capacity and low reduction potential. But its large-scale commercialization is hampered because of the infinite volume expansion, severe side reactions, and uncontrollable dendrite formation. Herein, the self-supporting porous lithium foam anode is obtained by a melt foaming method. The adjustable interpenetrating pore structure and dense Li₃N protective layer coating on the inner surface enable the lithium foam anode with great tolerance to electrode volume variation, parasitic reaction, and dendritic growth during cycling. Full cell using high areal capacity (4.0 mAh cm⁻²) LiNi0.8Co0.1Mn0.1 (NCM811) cathode with the N/P ratio of 2 and E/C ratio of 3 g Ah⁻¹ can stably operate for 200 times with 80% capacity retention. The corresponding pouch cell has <3% pressure fluctuation per cycle and almost zero pressure accumulation.     

Facile preparation of core@shell and concentration-gradient spinel particles for Li-ion battery cathode materials

Core@shell and concentration-gradient particles have attracted much attention as improved cathodes for Li-ion batteries (LIBs). However, most of their preparation routes have employed a precisely-controlled co-precipitation method. Here, we report a facile preparation route of core@shell and concentration-gradient spinel particles by dry powder processing. The core@shell particles composed of the MnO₂ core and the Li(Ni,Mn)₂O₄ spinel shell are prepared by mechanical treatment using an attrition-type mill, whereas the concentration-gradient spinel particles with an average composition of LiNi_0.32Mn_1.68O₄ are produced by calcination of their core@shell particles as a precursor. The concentration-gradient LiNi_0.32Mn_1.68O₄ spinel cathode exhibits the high discharge capacity of 135.3 mA h g⁻¹, the wide-range plateau at a high voltage of 4.7 V and the cyclability with a capacity retention of 99.4% after 20 cycles. Thus, the facile preparation route of the core@shell and concentration-gradient particles may provide a new opportunity for the discovery and investigation of functional materials as well as for the cathode materials for LIBs.     

Surface modification with oxygen vacancy in Li-rich layered oxide Li1.2Mn0.54Ni0.13Co0.13O2 for lithium-ion batteries

A couple of layered Li-rich cathode materials Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ without any carbon modification are successfully synthesized by solvothermal and hydrothermal methods followed by a calcination process. The sample synthesized by the solvothermal method (S-NCM) possesses more homogenous microstructure, lower cation mixing degree and more oxygen vacancies on the surface, compared to the sample prepared by the hydrothermal method (H-NCM). The S-NCM sample exhibits much better cycling performance, higher discharge capacity and more excellent rate performance than H-NCM. At 0.2 C rate, the S-NCM sample delivers a much higher initial discharge capacity of 292.3 mAh g⁻¹ and the capacity maintains 235 mAh g⁻¹ after 150 cycles (80.4% retention), whereas the corresponding capacity values are only 269.2 and 108.5 mAh g⁻¹ (40.3% retention) for the H-NCM sample. The S-NCM sample also shows the higher rate performance with discharge capacity of 118.3 mAh g⁻¹ even at a high rate of 10 C, superior to that (46.5 mAh g⁻¹) of the H-NCM sample. The superior electrochemical performance of the S-NCM sample can be ascribed to its well-ordered structure, much larger specific surface area and much more oxygen vacancies located on the surface.     

Enhanced cycling stability of microsized LiCoO2 cathode by Li4Ti5O12 coating for lithium ion battery

The effect of Li₄Ti₅O₁₂ (LTO) coating amount on the electrochemical cycling behavior of the LiCoO₂ cathode was investigated at the high upper voltage limit of 4.5 V. Li₄Ti₅O₁₂ (≤5 wt.%) is not incorporated into the host structure and leads to formation of uniform coating. The cycling performance of LiCoO₂ cathode is related with the amount of Li₄Ti₅O₁₂ coating. The initial capacity of the LTO-coated LiCoO₂ decreased with increasing Li₄Ti₅O₁₂ coating amount but showed enhanced cycling properties, compared to those of pristine material. The 3 wt.% LTO-coated LiCoO₂ has the best electrochemical performance, showing capacity retention of 97.3% between 2.5 V and 4.3 V and 85.1% between 2.5 V and 4.5 V after 40 cycles. The coulomb efficiency shows that the surface coating of Li₄Ti₅O₁₂ is beneficial to the reversible intercalation/de-intercalation of Li⁺. LTO-coated LiCoO₂ provides good prospects for practical application of lithium secondary batteries free from safety issues.     

Interfacial Engineering Coupled Valence Tuning of MoO3 Cathode for High‐Capacity and High‐Rate Fiber‐Shaped Zinc‐Ion Batteries

Aqueous Zn‐ion batteries (ZIBs) have garnered the researchers' spotlight owing to its high safety, cost effectiveness, and high theoretical capacity of Zn anode. However, the availability of cathode materials for Zn ions storage is limited. With unique layered structure along the [010] direction, α‐MoO₃ holds great promise as a cathode material for ZIBs, but its intrinsically poor conductivity severely restricts the capacity and rate capability. To circumvent this issue, an efficient surface engineering strategy is proposed to significantly improve the electric conductivity, Zn ion diffusion rate, and cycling stability of the MoO₃ cathode for ZIBs, thus drastically promoting its electrochemical properties. With the synergetic effect of Al₂O₃ coating and phosphating process, the constructed Zn//P‐MoO_3?x@Al₂O₃ battery delivers impressive capacity of 257.7 mAh g^?1 at 1 A g^?1 and superior rate capability (57% capacity retention at 20 A g^?1), dramatically surpassing the pristine Zn//MoO₃ battery (115.8 mAh g^?1; 19.7%). More importantly, capitalized on polyvinyl alcohol gel electrolyte, an admirable capacity (19.2 mAh cm^?3) as well as favorable energy density (14.4 mWh cm^?3; 240 Wh kg^?1) are both achieved by the fiber‐shaped quasi‐solid‐state ZIB. This work may be a great motivation for further research on molybdenum or other layered structure materials for high‐performance ZIBs.     

Highly Electrochemically‐Reversible Mesoporous Na2FePO4F/C as Cathode Material for High‐Performance Sodium‐Ion Batteries

As promising cathode materials, iron‐based phosphate compounds have attracted wide attention for sodium‐ion batteries due to their low cost and safety. Among them, sodium iron fluorophosphate (Na₂FePO₄F) is widely noted due to its layered structure and high operating voltage compared with NaFePO₄. Here, a mesoporous Na₂FePO₄F@C (M‐NFPF@C) composite derived from mesoporous FePO₄ is synthesized through a facile ball‐milling combined calcination method. Benefiting from the mesoporous structure and highly conductive carbon, the M‐NFPF@C material exhibits a high reversible capacity of 114 mAh g^?1 at 0.1 C, excellent rate capability (42 mAh g^?1 at 10 C), and good cycling performance (55% retention after 600 cycles at 5 C). The high plateau capacity obtained (>90% of total capacity) not only shows high electrochemical reversibility of the as‐prepared M‐NFPF@C but also provides high energy density, which mainly originates from its mesoporous structure derived from the mesoporous FePO₄ precursor. The M‐NFPF@C serves as a promising cathode material with high performance and low cost for sodium‐ion batteries.     

A High-Voltage,Dendrite-Free,and Durable Zn–Graphite Battery

The intrinsic advantages of metallic Zn, like high theoretical capacity (820 mAh g⁻¹), high abundance, low toxicity, and high safety have driven the recent booming development of rechargeable Zn batteries. However, the lack of high-voltage electrolyte and cathode materials restricts the cell voltage mostly to below 2 V. Moreover, dendrite formation and the poor rechargeability of the Zn anode hinder the long-term operation of Zn batteries. Here a high-voltage and durable Zn–graphite battery, which is enabled by a LiPF₆-containing hybrid electrolyte, is reported. The presence of LiPF₆ efficiently suppresses the anodic oxidation of Zn electrolyte and leads to a super-wide electrochemical stability window of 4 V (vs Zn/Zn²⁺). Both dendrite-free Zn plating/stripping and reversible dual-anion intercalation into the graphite cathode are realized in the hybrid electrolyte. The resultant Zn–graphite battery performs stably at a high voltage of 2.8 V with a record midpoint discharge voltage of 2.2 V. After 2000 cycles at a high charge–discharge rate, high capacity retention of 97.5% is achieved with ≈100% Coulombic efficiency.     

Effects of CeO2 coating uniformity on high temperature cycle life performance of LiMn2O4

CeO₂ is coated using different precipitants on the surface of LiMn₂O₄ in order to investigate the effect of CeO₂ coating uniformity on the cycle life performance at high temperature. CeO₂ is prepared by a precipitation method without the use of a surfactant. Ammonium carbonate or ammonium hydroxide is respectively used as a precipitant in order to control the morphology and particle size of CeO₂. More uniform coating layer composed of well dispersed CeO₂ nanoparticles is obtained with ammonium hydroxide while aggregation lead to non-uniform coating layer when ammonium carbonate is used. The CeO₂-coated LiMn₂O₄ shows better cyclability both at room temperature and 60 °C than the pristine sample but much higher capacity retention rate can be achieved by using ammonium hydroxide. The smaller particle size and uniform coating layer obtained using ammonium hydroxide appear to contribute to the better cycling performance.     

LiNi0.5Mn1.5O4 cathode material by low-temperature solid-state method with excellent cycleability in lithium ion battery

LiNi_0.5Mn_1.5O₄ cathode material was synthesized from a mixture of LiCl, NiCl₂?6H₂O and MnCl₂?4H₂O with 70 wt.% oxalic acid by a low-temperature solid-state method. The calcination temperature was adjusted to form disorder Fd3m structure at 700-800 °C for 10 h.XRD patterns and FTIR spectroscopy showed that the LiNi_0.5Mn_1.5O₄ cathode material exhibited an impurity-free spinel Fd3m structure. Electrochemical property results revealed that the LiNi_0.5Mn_1.5O₄ cathode material charged at 1C rate to 4.9 V and discharged at 2 and 3 C to 3.5 V delivered initial capacity of 120 mAh/g and maintained a capacity retention over 80% at room temperature after 1000 charge/discharge cycles.     

Preparation,characterization and catalytic properties of CuO/CeO2 system

CeO₂ nano-particles and CuO/CeO₂ system were prepared by sol-gel and impregnation methods and characterized using combined spectroscopic techniques of XRD, XPS, TPR, FT–Raman, BET and HRTEM. It was found the CeO₂ was cubic phase with fluorite structure and CuO was highly dispersed on the CeO₂ particles. Temperature-programmed reduction (TPR) showed a two-step reduction for CuO/CeO₂ catalysts. XPS analysis indicated the presence of redox couple Ce⁴⁺/Ce³⁺ and reduced copper species in the CuO/CeO₂ catalysts. The factors, such as calcination temperature, calcination time and CuO loading, influenced on the catalytic properties of CuO/CeO₂ catalysts.     

Singlet oxygen evolution from layered transition metal oxide cathode materials and its implications for lithium-ion batteries

For achieving higher energy density lithium-ion batteries, the improvement of cathode active materials is crucial. The most promising cathode materials are nickel-rich layered oxides LiNi_xCo_yMn_zO₂ (NCM) and over lithiated NCM (often called HE-NCM). Unfortunately, the full capacity of NCM cannot be utilized due to its limited cycle-life at high state-of-charge (SOC), while HE-NCM requires high voltages. By operando emission spectroscopy, we show for the first time that highly reactive singlet oxygen is released when charging NCM and HE-NCM to an SOC beyond ≈80%. In addition, on-line mass-spectrometry reveals the evolution of CO and CO₂ once singlet oxygen is detected, providing significant evidence for the reaction between singlet oxygen and electrolyte to be a chemical reaction. It is controlled by the SOC rather than by potential, as would be the case for a purely electrochemical electrolyte oxidation. Singlet oxygen formation therefore imposes a severe challenge to the development of high-energy batteries based on layered oxide cathodes, shifting the focus of research from electrochemically stable 5?V-electrolytes to chemical stability toward singlet oxygen.     

Solution combustion synthesis of LiMn2O4 fine powders for lithium ion batteries

In this work, fine powders of spinel-type LiMn₂O₄ as cathode materials for lithium ion batteries (LIBs) were produced by a facile solution combustion synthesis using glycine as fuel and metal nitrates as oxidizers. Single phase of LiMn₂O₄ products were successfully prepared by SCS with a subsequent calcination treatment at 600–1000 °C. The structure and morphology of the powders were studied in detail by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The electrochemical properties were characterized by galvanostatic charge–discharge cycling and cyclic voltammetry. The crystallinity, morphology, and size of the products were greatly influenced by the calcination temperature. The sample calcined at 900 °C had good crystallinity and particle sizes between 500 and 1000 nm. It showed the best performance with an initial discharge capacity of 115.6 mAh g⁻¹ and a capacity retention of 93% after 50 cycles at a 1 C rate. In comparison, the LiMn₂O₄ sample prepared by the solid-state reaction showed a lower capacity of around 80 mAh g⁻¹.     

LiNi0.5Co0.2Mn0.3O2@WO3复合正极材料的制备与性能

为改善LiNi_0.5Co_0.2Mn_0.3O₂（NCM）锂离子电池三元正极材料的电化学性能,采用液相蒸发法将WO₃包覆于NCM表面,得到NCM@WO₃复合正极材料。通过XRD、SEM和TEM对NCM@WO₃复合材料的结构和形貌进行表征,利用充放电测试、循环伏安及交流阻抗测试对其电化学性能进行表征。结果表明,当WO₃包覆量为3wt%时,NCM@WO₃复合材料性能最佳,在0.5 C下的首次放电比容量为179.9 mA·hg-1,不可逆容量损失降低至42.4 mA·hg-1,循环50圈后容量保持率为98.3%。WO₃的包覆提高了锂离子扩散速率,减少了电极材料与电解液的副反应,NCM@WO₃复合材料的电化学性能得到提升。