Electrochemical Degradation Mechanism and Thermal Behaviors of the Stored LiNi0.5Co0.2Mn0.3O2 Cathode Materials

In Situ Forming Asymmetric Gel Polymer Electrolyte Enhances the Performance of High-Voltage Lithium Metal Batteries

With the rapid evolution of electric vehicle technology, concerns regarding range anxiety and safety have become increasingly pronounced. Battery systems with high specific energy and enhanced security, featuring ternary cathodes paired with lithium (Li) metal anodes, are poised to emerge as next-generation electrochemical devices. However, the asymmetric configuration of the battery structure, characterized by the robust oxidative behavior of the ternary cathodes juxtaposed with the vigorous reductive activity of the Li metal anodes, imposes elevated requisites for the electrolytes. Herein, a well-designed gel polymer electrolyte with asymmetric structure was successfully prepared based on the Ritter reaction of cyanoethyl poly(vinyl alcohol) (PVA-CN) and cationic ring-opening polymerization of s-Trioxane. With the aid of the sieving effect of separator, the in situ asymmetric gel polymer electrolyte has good compatibility with both the high-voltage cathodes and Li anodes. The amide groups generated by PVA-CN after the Ritter reaction and additional cyano groups can tolerate high voltages up to 5.1 V, matching with ternary cathodes without any challenges. The functional amide and cyano groups participate in the formation of the cathode electrolyte interface and stabilize the cathode structure. Meanwhile, the in situ formed ether-based polyformaldehyde electrolyte is beneficial for promoting uniform Li deposition on anode surfaces. Li-Li symmetric cells demonstrate sustained stability over 2000 h of cycling at a current density of 1 mA cm-2 for 1 mAh cm-2. Furthermore, the capacity retention rate of Li(Ni0.6Mn0.2Co0.2)O2-Li cells with 0.5 C cycling after 300 cycles is 92.2%, demonstrating excellent cycle stability. The electrolyte preparation strategy provides a strategy for the progress of high-performance electrolytes and promotes the rapid development of high-energy-density Li metal batteries.

Failure of Lithium-Ion Batteries Accelerated by Gravity

The safety concerns surrounding lithium-ion batteries (LIBs) have garnered increasing attention due to their potential to endanger lives and incur significant financial losses. However, the origins of battery failures are diverse, presenting significant challenges in developing safety measures to mitigate accidental catastrophes. In this study, the aging mechanism of LiNi0.5Co0.2Mn0.3O2||graphite-based cylindrical 18,650 LIBs stored at room temperature for two years was investigated. It was found that an uneven distribution of electrolytes can be caused by gravity, leading to temperature variations within the battery. Specifically, it was observed that the temperature at the top of the battery was approximately -0.89 °C higher than at the bottom, correlating with an increase in partial internal resistance. Additionally, upon disassembly and analysis of spent batteries, the most significant damage to electrode materials at the top of the battery was observed. These findings suggest that gravity-induced electrolyte insufficiency exacerbates side reactions, particularly at the top of the battery. This study offers a unique perspective on the safety concerns associated with high-energy-density batteries in long-term and large-scale applications.

Topotactic Transformation of Surface Structure Enabling Direct Regeneration of Spent Lithium-Ion Battery Cathodes

Recycling spent lithium-ion batteries (LIBs) has become an urgent task to address the issues of resource shortage and potential environmental pollution. However, direct recycling of the spent LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) cathode is challenging because the strong electrostatic repulsion from a transition metal octahedron in the lithium layer provided by the rock salt/spinel phase that is formed on the surface of the cycled cathode severely disrupts Li⁺ transport, which restrains lithium replenishment during regeneration, resulting in the regenerated cathode with inferior capacity and cycling performance. Here, we propose the topotactic transformation of the stable rock salt/spinel phase into Ni_0.5Co_0.2Mn_0.3(OH)₂ and then back to the NCM523 cathode. As a result, a topotactic relithiation reaction with low migration barriers occurs with facile Li⁺ transport in a channel (from one octahedral site to another, passing through a tetrahedral intermediate) with weakened electrostatic repulsion, which greatly improves lithium replenishment during regeneration. In addition, the proposed method can be extended to repair spent NCM523 black mass, spent LiNi_0.6Co_0.2Mn_0.2O₂, and spent LiCoO₂ cathodes, whose electrochemical performance after regeneration is comparable to that of the commercial pristine cathodes. This work demonstrates a fast topotactic relithiation process during regeneration by modifying Li⁺ transport channels, providing a unique perspective on the regeneration of spent LIB cathodes.

High Value-Added Utilization of Waste Hydrodesulfurization Catalysts: Low-Cost Synthesis of Cathode Materials for Lithium-Ion Batteries

This work introduces a one-step method for the preparation of layered oxide cathode materials utilizing pure Ni and Co mixed solution obtained from the waste hydrodesulfurization (HDS) catalyst. An efficient non-separation strategy with pyrometallurgical-hydrometallurgical (pyro-hydrometallurgical) process consisting of roasting and leaching is proposed. Most of the impurity metal elements such as Mo and V were removed by simple water leaching after the waste HDS catalyst was roasted with Na2CO3 at 650 °C for 2.5 h. Additionally, 93.9% Ni and 100.0% Co were recovered by H2SO4 leaching at 90 °C for 2.5 h. Then, LiNi0.533Co0.193Mn0.260V0.003Fe0.007Al0.004O2 (C–NCM) was successfully synthesized by hydroxide co-precipitation and high temperature solid phase methods using the above Ni and Co mixed solution. The final C–NCM material exhibits excellent electrochemical performance with a discharge specific capacity of 199.1 mAh g−1 at 0.1 C and a cycle retention rate of 79.7% after 200 cycles at 1 C. This novel process for the synthesis of cathode material can significantly improve production efficiency and realize the high added-value utilization of metal resources in a waste catalyst.

Insight into the Redox Reaction Heterogeneity within Secondary Particles of Nickel-Rich Layered Cathode Materials

Nickel-rich LiNi_xCo_yMn_1-x-yO₂ (nickel-rich NCM, 0.6 ≤ x < 1) cathode materials suffer from multiscale reaction heterogeneity within the electrode during the electrochemical energy storage process. However, owing to the lack of appropriate diagnostic tools, the systematic understanding and observation on the redox reaction heterogeneity at the individual secondary-particle level is still limited. Raman spectroscopy can not only reflect the depth of the redox reaction through probing the vibrational information on the metal-oxygen coordination structure but also sensitively detect the local structure changes of different regions within the secondary particle with suitable spatial resolution. Therefore, Raman spectroscopy is applied here to conveniently conduct the high-resolution and in-depth analysis of the rate-dependent reaction heterogeneity within nickel-rich NCM secondary particles. It is found that, under high-rate conditions, the oxidation/reduction reaction mainly occurs in the surface region of the particles and the cause of this particle-scale reaction heterogeneity is the limitation of the slow solid-phase Li⁺ diffusion and the transient charging/discharging processes. In addition, this reaction heterogeneity would aggravate the structural instability of the material continuously during the charging/discharging cycles, thus resulting in a slowdown in the kinetics of Li⁺ de/intercalation and the apparent capacity decay. This work can not only provide fundamental insight into the rational modification of high-power nickel-rich NCM materials but also guide the setting of electrochemical operating conditions for high-power lithium-ion batteries (LIBs).

One-Spot Facile Synthesis of Single-Crystal LiNi0.5Co0.2Mn0.3O2 Cathode Materials for Li-ion Batteries

The layered lithium-metal oxides are promising cathode materials for Li-ion batteries. Nevertheless, their widespread applications have been limited by the high cost, complex process, and poor stability resulting from the Ni²⁺/Li⁺ mixing. Hence, we have developed a facile one-spot method combining glucose and urea to form a deep eutectic solvent, which could lead to the homogeneous distribution and uniform mixing of transition-metal ions at the atomic level. LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) polyhedron with high homogeneity could be obtained through in situ chelating Ni²⁺, Co³⁺, and Mn⁴⁺ by the amid groups. The prepared material exhibits a relatively high initial electrochemical property, which is due to the unique single-crystal hierarchical porous nano/microstructure, the polyhedron with exposed active surfaces, and the negligible Ni²⁺/Li⁺ mixing level. This one-spot approach could be expanded to manufacture other hybrid transition-metal-based cathode materials for batteries.

La4NiLiO8-Shielded Layered Cathode Materials for Emerging High-Performance Safe Batteries

Low theoretical capacities of the commercial cathode materials (olivine: ∼170 mA h g^-1 and spinel: ∼140 mA h g^-1) dictate the need for higher energy density alternates such as nickel-rich (denotes as NCM) materials with a theoretical capacity of ∼270 mA h g^-1. However, low conductivity and the bulk degradation after direct contact with liquid electrolytes, especially at temperatures higher than 50 °C, are the biggest issues to resolve for safe use and confident commercialization of the NCM materials. In this context, we first report "La₄NiLiO₈ shields" to simultaneously boost charge conduction characteristics and circumvent the electrolytic degradation of NCM. Consequently, the La₄NiLiO₈-shielded LiNi_0.5Co_0.2Mn_0.3O₂ (LSN5) not only offers a 4.1× less charge transfer resistance and significantly higher discharge capacity (219.7 mA h g^-1) than the nonshielded NCM (187 mA h g^-1) and theoretical capacities of commercial cathode materials but also maintains more than 91.7% of capacity retention at 25 °C after 500 cycles and 84.2% at 60 °C after 200 cycles. In contrast, the nonshielded NCM cathodes can only provide 58.9 and 45.5% capacity retentions at corresponding test temperatures and performance cycles. The acquired excellent electrochemical performance and battery stability at both the ambient and high-temperature conductions infer great importance of the novel La₄NiLiO₈ shields in developing high-performance safe secondary batteries.

Surface double coating of a LiNiaCobAl1−a−bO2 (a > 0.85) cathode with TiOx and Li2CO3 to apply a water-based hybrid polymer binder to Li-ion batteries

Recently a water-based polymer binder has been getting much attention because it simplifies the production process of lithium ion batteries (LIBs) and reduce their cost. The surface of LiNi_aCo_bAl_1−a−bO₂ (a > 0.85, NCA) cathode with a high voltage and high capacity was coated doubly with water-insoluble titanium oxide (TiO_x) and Li₂CO₃ layers to protect the NCA surface from the damage caused by contacting with water during its production process. The TiO_x layer was at first coated on the NCA particle surface with a tumbling fluidized-bed granulating/coating machine for producing TiO_x-coated NCA. However, the TiO_x layer could not coat the NCA surface completely. In the next place, the coating of the TiO_x-uncoated NCA surface with Li₂CO₃ layer was conducted by bubbling CO₂ gas in the TiO_x-coated NCA aqueous slurry on the grounds that Li₂CO₃ is formed through the reaction between CO₃²⁻ ions and residual LiOH on the TiO_x-uncoated NCA surface, resulting in the doubly coated NCA particles (TiO_x/Li₂CO₃-coated NCA particles). The Li₂CO₃ coating is considered to take place on the TiO_x layer as well as the TiO_x-uncoated NCA surface. The results demonstrate that the double coating of the NCA surface with TiO_x and Li₂CO₃ allows for a high water-resistance of the NCA surface and consequently the TiO_x/Li₂CO₃-coated NCA particle cathode prepared with a water-based binder possesses the same charge/discharge performance as that obtained with a “water-uncontacted” NCA particle cathode prepared using the conventional organic solvent-based polyvinylidene difluoride binder.

Recently a water-based polymer binder has been getting much attention because it simplifies the production process of lithium ion batteries (LIBs) and reduce their cost.

Interface Interaction Behavior of Self-Terminated Oligomer Electrode Additives for a Ni-Rich Layer Cathode in Lithium-Ion Batteries: Voltage and Temperature Effects

Self-terminated oligomer additives synthesized from bismaleimide and barbituric acid derivatives improve the safety and performance of lithium-ion batteries (LIBs). This study investigates the interface interaction of these additives and the cathode material. Two additives were synthesized by Michael addition (additive A) and aza-Michael addition (additive B). The electrochemical performances of bare and modified LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622) materials are studied. The cycling stability and rate capability of NMC622 considerably improve on surface modification with additive B. According to the differential scanning calorimetry results, the exothermic heat of fully deliathiated NMC622 is dramatically decreased through surface modification with both additives. The electrode surface kinetics and interface interaction phenomena of the additives are determined through surface plasma resonance measurements in operando gas chromatography-mass spectroscopy (GCMS) and in situ soft X-ray absorption spectroscopy (XAS). The binding rate constant of additive B onto NMC622 particles is 1.2-2.3 × 10⁴ M^-1 s^-1 in the temperature range of 299-311 K, which is ascribed to the strong binding affinity toward the electrode surface. This affinity enhances Li⁺ diffusion, which allows the electrode modified by additive B to provide high electrochemical performance with superior thermal stability. In operando GCMS reveals that gas evolution due to the electrolyte degradation at the NMC622 surface contributes to safety hazards in the bare NMC622 material. In situ soft XAS indicates the occurrence of structural transformation in the bare NMC622 material after it is fully charged and at elevated temperatures. The NMC622 material is stabilized by incorporating additives. The unique performance of additive B can be attributed to its linear structure that allows superior electrode surface adhesion compared with that of additive A. Therefore, this study presents an optimized working principle of self-terminated oligomers, which can be developed and applied to improve the safety and performance of LIBs.

Studies of air-exposure effects and remediation measures on lithium bis(oxalato)borate

Changes in properties for air-exposure lithium bis(oxalate)borate and reparability study by heating method.

Compound-Hierarchical-Sphere LiNi0.5Co0.2Mn0.3O2: Synthesis, Structure, and Electrochemical Characterization

Compound-hierarchical-sphere-structured LiNi_0.5Co_0.2Mn_0.3O₂ was synthesized to improve the electrochemical performance of this material in lithium-ion battery cathodes. The product was found to have a large specific surface area, good electron and ion conductivities, a stable interface, and a robust nano/microhierarchical structure, all of which improved the rate capability, capacity, and cycling stability of this material. When this material was cycled between 3.0 and 4.3 V, a high discharge capacity of 180.8 mA h g^-1 was obtained at 0.2C with 94.0% capacity retention after 100 cycles. In addition, a superior discharge capacity of 148.9 mA h g^-1 was observed at a high current density of 1600 mA g^-1. This compound-hierarchical-sphere LiNi_0.5Co_0.2Mn_0.3O₂ is readily prepared using our ternary coprecipitation method. We also propose an effector unit theory to explain the enhanced cycling stability of this substance and believe that the present results will assist in the design of cathode materials for lithium-ion batteries.