Surface Growth and Intergranular Separation of Polycrystalline Particles for Regeneration of Stable Single-Crystal Cathode Materials

Regenerated Ni-Doped LiCoO2 from Spent Lithium-Ion Batteries as a Stable Cathode at 4.5 V

In the context of the increasing number of spent lithium-ion batteries, it is urgent to explore cathode regeneration and upcycling solutions to reduce environmental pollution, promote resource reuse, and meet the demand for high-energy cathode materials. Here, a closed-loop recycling method is introduced, which not only reclaims cobalt and lithium elements from spent lithium-ion batteries but also converts them into high-voltage LiCoO2 (LCO) materials. This approach involved pretreatment, chlorination roasting, water leaching, and ion doping to regenerate nickel-doped LCO (Ni-RLCO) materials. The doping of nickel effectively enhances the electrochemical stability of the LCO cathode at 4.5 V. The Ni-RLCO cathode exhibited a high discharge specific capacity of 185.28 mAh/g at a rate of 0.5 C with a capacity retention of 86.3% after 50 cycles and excellent rate capacity of 156.21 mAh/g at 2 C. This work offers a approach in significance for upcycling spent LCO into high-energy-density batteries with long-term cycling stability under high voltage.

Direct Regeneration of Spent Lithium-Ion Battery Cathodes: From Theoretical Study to Production Practice

Direct regeneration method has been widely concerned by researchers in the field of battery recycling because of its advantages of in situ regeneration, short process and less pollutant emission. In this review, we firstly analyze the primary causes for the failure of three representative battery cathodes (lithium iron phosphate, layered lithium transition metal oxide and lithium cobalt oxide), targeting at illustrating their underlying regeneration mechanism and applicability. Efficient stripping of material from the collector to obtain pure cathode material has become a first challenge in recycling, for which we report several pretreatment methods currently available for subsequent regeneration processes. We review and discuss emphatically the research progress of five direct regeneration methods, including solid-state sintering, hydrothermal, eutectic molten salt, electrochemical and chemical lithiation methods. Finally, the application of direct regeneration technology in production practice is introduced, the problems exposed at the early stage of the industrialization of direct regeneration technology are revealed, and the prospect of future large-scale commercial production is proposed. It is hoped that this review will give readers a comprehensive and basic understanding of direct regeneration methods for used lithium-ion batteries and promote the industrial application of direct regeneration technology.

Fundamentals, status and challenges of direct recycling technologies for lithium ion batteries

Advancement in energy storage technologies is closely related to social development. However, a significant conflict has arisen between the explosive growth in battery demand and resource availability. Facing the upcoming large-scale disposal problem of spent lithium-ion batteries (LIBs), their recycling technology development has become key. Emerging direct recycling has attracted widespread attention in recent years because it aims to 'repair' the battery materials, rather than break them down and extract valuable products from their components. To achieve this goal, a profound understanding of the failure mechanisms of spent LIB electrode materials is essential. This review summarizes the failure mechanisms of LIB cathode and anode materials and the direct recycling strategies developed. We systematically explore the correlation between the failure mechanism and the required repair process to achieve efficient and even upcycling of spent LIB electrode materials. Furthermore, we systematically introduce advanced in situ characterization techniques that can be utilized for investigating direct recycling processes. We then compare different direct recycling strategies, focussing on their respective advantages and disadvantages and their applicability to different materials. It is our belief that this review will offer valuable guidelines for the design and selection of LIB direct recycling methods in future endeavors. Finally, the opportunities and challenges for the future of battery direct recycling technology are discussed, paving the way for its further development.

Stacking Fault Formation in LiNi0.6Co0.2Mn0.2O2 during Cycling: Fundamental Insights into the Direct Recycling of Spent Lithium-Ion Batteries

As the global marketplace for lithium-ion batteries (LIBs) proliferates, technologies for efficient and environmentally friendly recycling, i.e., direct recycling, of spent LIBs are urgently required. In this contribution, we elucidated the mechanisms underlying the degradation that occurs during the cycling of a Li/LiNi0.6Co0.2Mn0.2O2 (NCM622) cell. The results provided fundamental insights into the optimum procedures for direct recycling using a recently developed, state-of-the-art positive electrode material. Capacity fade in NCM622 was induced by cycling at high voltages above 4.6 V vs Li+/Li, during which the rhombohedral symmetry approached cubic symmetry. The selective line broadening and peak shifts that appeared in the X-ray diffraction patterns after cycling indicated the formation of stacking faults along the ch-axis. In addition, high-resolution transmission electron microscopy clarified that rock-salt domains were located on the NCM622 surface before and after cycling. These structural analyses confirmed that the NCM622 particles degrade not at their surfaces but rather in the bulk, contradicting previous reports where degradation during cycling is mainly caused by rock-salt domains on the surface. Material regeneration processes involving the restoration of the original stacking sequence are essential for effective direct recycling.

Polycrystal Li2ZnTi3O8/C anode with lotus seedpod structure for high-performance lithium storage

Lotus-seedpod structured Li₂ZnTi₃O₈/C (P-LZTO) microspheres obtained by the molten salt method are reported for the first time. The received phase-pure Li₂ZnTi₃O₈ nanoparticles are inserted into the carbon matrix homogeneously to form a Lotus-seedpod structure, as confirmed by the morphological and structural measurements. As the anode for lithium-ion batteries, the P-LZTO material demonstrates excellent electrochemical performance with a high rate capacity of 193.2 mAh g^-1 at 5 A g^-1 and long-term cyclic stability up to 300 cycles at 1 A g^-1. After even 300 cyclings, the P-LZTO particles can maintain their morphological and structural integrity. The superior electrochemical performances have arisen from the unique structure where the polycrystalline structure is beneficial for shorting the lithium-ion diffusion path, while the well-encapsulated carbon matrix can not only enhance the electronic conductivity of the composite but also alleviate the stress anisotropy during lithiation/delithiation process, leading to well-preserved particles.

Enhanced Cyclability of LiNi0.6Co0.2Mn0.2O2 Cathodes by Integrating a Spinel Interphase in the Grain Boundary

Nickel-rich layered oxides are promising cathode materials for high-energy-density lithium-ion batteries. Unfortunately, the interfacial instability and intergranular cracks result in fast capacity fading and voltage fading during battery cycling. To address these issues, a coherent spinel interphase in the grain boundary of LiNi_0.6Co_0.2Mn_0.2O₂ (NCM) was successfully constructed via solution infusion and heat treatment. The results showed that the spinel (LiMn₂O₄) interphase could significantly reduce the formation of intergranular cracks during cycling. Meanwhile, the spinel structure on the primary particles effectively suppressed surface degradation, realizing the reduction of interface charge-transfer resistance and electrochemical polarization. As a result, the spinel-modified NCM cathode materials display superior electrochemical cyclability. The 1 wt % spinel phase-modified NCM delivers a discharge capacity of 154.1 mAh g^-1 after 300 cycles (1 C, 3-4.3 V) with an excellent capacity retention of 93%.