High-performing LiMgxCuyCo₁-x-yO₂ cathode material for lithium rechargeable batteries

Enhancing the Stability of 4.6 V LiCoO2 Cathode Material via Gradient Doping

LiCoO2 (LCO) can deliver ultrahigh discharge capacities as a cathode material for Li-ion batteries when the charging voltage reaches 4.6 V. However, establishing a stable LCO cathode at a high cut-off voltage is a challenge in terms of bulk and surface structural transformation. O2 release, irreversible structural transformation, and interfacial side reactions cause LCO to experience severe capacity degradation and safety problems. To solve these issues, a strategy of gradient Ta doping is proposed to stabilize LCO against structural degradation. Additionally, Ta1-LCO that was tuned with 1.0 mol% Ta doping demonstrated outstanding cycling stability and rate performance. This effect was explained by the strong Ta-O bonds maintaining the lattice oxygen and the increased interlayer spacing enhancing Li+ conductivity. This work offers a practical method for high-energy Li-ion battery cathode material stabilization through the gradient doping of high-valence elements.

Improvement of Thermodynamic Phase Stability and High-Rate Capability of Li Layered Oxides

The use of elemental doping in lithium cobalt oxide (LCO) cathode material at high cutoff voltage is a widely adopted technique in the field of rechargeable batteries to mitigate multiple unfavorable phase transitions. However, there is still a lack of fundamental understanding regarding the rationality of each doping element implemented in this method, specifically considering the various thermodynamic stability and phase transitions. Herein, we investigated the effect of Ti doping on an O2 phase LCO (LCTO) cathode material that exhibited enhanced rate performance. We suggest that the incorporation of Ti into an O2 phase LCO results in the mitigation of multiple-phase transitions and the improvement of phase stability, thereby yielding a high-rate-capable cathode material. Through a combination of experimental and computational calculations, we demonstrate that Ti doping improves the thermodynamic stability and kinetics of Li-ions during the cycling process.

Atomic Layer Deposition of Alumina-Coated Thin-Film Cathodes for Lithium Microbatteries

This work shows the electrochemical performance of sputter-deposited, binder-free lithium cobalt oxide thin films with an alumina coating deposited via atomic layer deposition for use in lithium-metal-based microbatteries. The Al₂O₃ coating can improve the charge-discharge kinetics and suppress the phase transition that occurs at higher potential limits where the crystalline structure of the lithium cobalt oxide is damaged due to the formation of Co⁴⁺, causing irreversible capacity loss. The electrochemical performance of the thin film is analysed by imposing 4.2, 4.4 and 4.5 V upper potential limits, which deliver improved performances for 3 nm of Al₂O₃, while also highlighting evidence of Al doping. Al₂O₃-coated lithium cobalt oxide of 3 nm is cycled at 147 µA cm^-2 (~2.7 C) to an upper potential limit of 4.4 V with an initial capacity of 132 mAh g^-1 (65.7 µAh cm^-2 µm^-1) and a capacity retention of 87% and 70% at cycle 100 and 400, respectively. This shows the high-rate capability and cycling benefits of a 3 nm Al₂O₃ coating.

Nanoscale control and tri-element co-doping of 4.6 V LiCoO2 with excellent rate capability and long-cycling stability for lithium-ion batteries

Structural instability at high voltage severely restricts the reversible capacity of the LiCoO₂ cathode. Moreover, the main difficulties in achieving high-rate performance of LiCoO₂ are the long Li⁺ diffusion distance and slow Li⁺ intercalation/extraction during the cycle. Thus, we designed a modification strategy of nanosizing and tri-element co-doping to synergistically enhance the electrochemical performance of LiCoO₂ at high voltage (4.6 V). Mg, Al, and Ti co-doping maintains the structural stability and phase transition reversibility, which promotes the cycling performance of LiCoO₂. After 100 cycles at 1 C, the capacity retention of the modified LiCoO₂ reached 94.3%. In addition, the tri-elemental co-doping increases Li⁺ interlayer spacing and enhances Li⁺ diffusivity by tens of times. Simultaneously, nanosize modification decreases Li⁺ diffusion distance, leading to a significantly enhanced rate capacity of 132 mA h g^-1 at 10 C, much better than that of the unmodified LiCoO₂ (2 mA h g^-1). After 600 cycles at 5 C, the specific capacity remains at 135 mA h g^-1 with a capacity retention of 91%. The nanosizing co-doping strategy synchronously enhanced the rate capability and cycling performance of LiCoO₂.

Advancing to 4.6 V Review and Prospect in Developing High-Energy-Density LiCoO2 Cathode for Lithium-Ion Batteries

Layered LiCoO₂ (LCO) is one of the most important cathodes for portable electronic products at present and in the foreseeable future. It becomes a continuous push to increase the cutoff voltage of LCO so that a higher capacity can be achieved, for example, a capacity of 220 mAh g^-1 at 4.6 V compared to 175 mAh g^-1 at 4.45 V, which is unfortunately accompanied by severe capacity degradation due to the much-aggravated side reactions and irreversible phase transitions. Accordingly, strict control on the LCO becomes essential to combat the inherent instability related to the high voltage challenge for their future applications. This review begins with a discussion on the relationship between the crystal structures and electrochemical properties of LCO as well as the failure mechanisms at 4.6 V. Then, recent advances in control strategies for 4.6 V LCO are summarized with focus on both bulk structure and surface properties. One closes this review by presenting the outlook for future efforts on LCO-based lithium ion batteries (LIBs). It is hoped that this work can draw a clear map on the research status of 4.6 V LCO, and also shed light on the future directions of materials design for high energy LIBs.

Constructing compatible interface between Li7La3Zr2O12 solid electrolyte and LiCoO2 cathode for stable cycling performances at 4.5 V

With high theoretical capacity and tap density, LiCoO2 (LCO) cathode has been extensively utilized in lithium-ion batteries (LIBs) for energy storage devices. However, the bottleneck of structural and interfacial instabilities upon cycling severely restricts its practical application at high cut-off voltage. From another perspective, the compatibility between the electrode and electrolyte is highly valued in the development of all-solid-state batteries. Herein, we construct a compatible interface between Li7La3Zr2O12 (LLZO) and LCO through a facile surface modification strategy, which significantly improves the cycling stability of LCO at a high cut-off voltage of 4.5 V. Characterization results demonstrate that the LCO@1.0 LLZO sample delivers a desirable capacity retention of 76.8% even after 1000 cycles at 3.0-4.5 V with the current density of 1 C (1 C = 274 mA g-1). Further investigation indicates that the LLZO modification layer could protect the LCO electrode through effectively alleviating the side reactions, which not only facilitates the Li+ transportation at the interface but also mitigates the bulk structure degradation. Moreover, it is also established that a small amount of La and Zr ions could gradiently migrate into the surface lattice of LCO to generate a thin layer of the surface solid solution Li-Co-La-Zr-O. Thus formed pinning region between surface modified LLZO and LCO cathode could contribute both to their mechanical compatibility and Li+ kinetics behavior upon repeated cycling. This work not only provides a strategy in broadening the operation potential and extracting higher capacity of LCO but also sheds light on constructing compatible interfaces in LIBs, especially for all-solid-state energy storage and conversion devices.

A first-principles study on the properties of Sn-doped LiCoO2 for Li-ion batteries

The key for the application of LiCoO₂ as a lithium-ion battery electrode at high voltage is to suppress the irreversible phase transformation from the layered to the spinel/rocksalt structure during cycling. The experimental study (R. Zhao, J. Zhang, G.-H. Lee, K. Zhang, V. W.-H. Lau, J.-J. Lee, I. Moudrakovski, Y.-L. Yang, F. Zou, M. Park, I. M. Hung and Y.-M. Kang, J. Mater. Chem. A, 2020, 8, 12424) demonstrated that Sn doping into LiCoO₂ effectively inhibits the undesired phase transition and ascribed the structural stability to the ability of the Sn dopant to pin the lattice thermal vibration. However, the detailed information on Sn-doped LiCoO₂, such as atomic structures, still remains uncovered. Here, we carried out a comprehensive theoretical study on un-doped and Sn-doped LiCoO₂ with the aid of first-principles calculations. Our study shows that the un-doped and Sn-doped systems investigated in the experiment should contain Co-O vacancies and Sn prefers to be doped at the site that is near to the Co-O vacancies. The study also demonstrates that Sn-doping can significantly decrease the variation in volume and inhibit Co migration during delithiation. Additionally, Sn-doping can reduce the average activation barrier of Li diffusion. The theoretical study gives an insight into the microscopic mechanism of Sn-doping to enhance the performance of LiCoO₂ as a cathode material and is a necessary complement to the experimental study.

Recycling lithium-ion batteries from electric vehicles

Rapid growth in the market for electric vehicles is imperative, to meet global targets for reducing greenhouse gas emissions, to improve air quality in urban centres and to meet the needs of consumers, with whom electric vehicles are increasingly popular. However, growing numbers of electric vehicles present a serious waste-management challenge for recyclers at end-of-life. Nevertheless, spent batteries may also present an opportunity as manufacturers require access to strategic elements and critical materials for key components in electric-vehicle manufacture: recycled lithium-ion batteries from electric vehicles could provide a valuable secondary source of materials. Here we outline and evaluate the current range of approaches to electric-vehicle lithium-ion battery recycling and re-use, and highlight areas for future progress.

Reviving lithium cobalt oxide-based lithium secondary batteries-toward a higher energy density

This review summarizes the key challenges, effective modification strategies and perspectives regarding reviving lithium cobalt oxide-based lithium secondary batteries-toward a higher energy density.

Countering the Segregation of Transition-Metal Ions in LiMn1/3 Co1/3 Ni1/3 O2 Cathode for Ultralong Life and High-Energy Li-Ion Batteries

High-voltage layered lithium transition-metal oxides are very promising cathodes for high-energy Li-ion batteries. However, these materials often suffer from a fast degradation of cycling stability due to structural evolutions. It seriously impedes the large-scale application of layered lithium transition-metal oxides. In this work, an ultralong life LiMn1/3 Co1/3 Ni1/3 O2 microspherical cathode is prepared by constructing an Mn-rich surface. Its capacity retention ratio at 700 mA g(-1) is as large as 92.9% after 600 cycles. The energy dispersive X-ray maps of electrodes after numerous cycles demonstrate that the ultralong life of the as-prepared cathode is attributed to the mitigation of TM-ions segregation. Additionally, it is discovered that layered lithium transition-metal oxide cathodes with an Mn-rich surface can mitigate the segregation of TM ions and the corrosion of active materials. This study provides a new strategy to counter the segregation of TM ions in layered lithium transition-metal oxides and will help to the design and development of high-energy cathodes with ultralong life.

Synthesis of high-voltage (4.7 V) LiCoO2 cathode materials with Al doping and conformal Al2O3 coating by atomic layer deposition

The electrochemical properties of high-voltage (4.7 V) LiCoO₂ cathode materials with Al doping and a conformal Al₂O₃ coating by atomic layer deposition were studied in this paper.

Underlying mechanisms of the synergistic role of Li2MnO3 and LiNi1/3Co1/3Mn1/3O2 in high-Mn, Li-rich oxides

Synergistic roles of Li₂MnO₃ and NCM experimentally observed in high-Mn, Li-rich oxides were theoretically elucidated through the crystal field stabilisation of electronic structures, which reveals that NCM stabilises the transition metal layer of Li₂MnO₃.

Improving the electrochemical properties of LiNi0.5Co0.2Mn0.3O2 at 4.6 V cutoff potential by surface coating with Li2TiO3 for lithium-ion batteries

The Li₂TiO₃-coated LiNi_0.5Co_0.2Mn_0.3O₂ (LTO@NCM) cathode materials are synthesized via an in situ coprecipitation method to improve the electrochemical performance of NCM.

Improved electrochemical performance of LiCoO₂ electrodes with ZnO coating by radio frequency magnetron sputtering

Surface modification of LiCoO2 is an effective method to improve its energy density and elongate its cycle life in an extended operation voltage window. In this study, ZnO was directly coated on as-prepared LiCoO2 composite electrodes via radio frequency (RF) magnetron sputtering. ZnO is not only coated on the electrode as thin film but also diffuses through the whole electrode due to the intrinsic porosity of the composite electrode and the high diffusivity of the deposited species. It was found that ZnO coating can significantly improve the cycling performance and the rate capability of the LiCoO2 electrodes in the voltage range of 3.0-4.5 V. The sample with an optimum coating thickness of 17 nm exhibits an initial discharge capacity of 191 mAh g(-1) at 0.2 C, and the capacity retention is 81% after 200 cycles. It also delivers superior rate performance with a reversible capacity of 106 mAh g(-1) at 10 C. The enhanced cycling performance and rate capability are attributed to the stabilized phase structure and improved lithium ion diffusion coefficient induced by ZnO coating as evidenced by X-ray diffraction, cyclic voltammetry, respectively.

Microwave-assisted synthesis of high-voltage nanostructured LiMn1.5Ni0.5O4 spinel: tuning the Mn3+ content and electrochemical performance

The LiMn1.5Ni0.5O4 spinel is an important lithium ion battery cathode material that has continued to receive major research attention because of its high operating voltage (∼4.8 V). This study interrogates the impact of microwave irradiation on the Mn(3+) concentration and electrochemistry of the LiMn1.5Ni0.5O4 spinel. It is shown that microwave is capable of tuning the Mn(3+) content of the spinel for enhanced electrochemical performance (high capacity, high capacity retention, excellent rate capability, and fast Li(+) insertion/extraction kinetics). This finding promises to revolutionize the application of microwave irradiation for improved performance of the LiMn1.5Ni0.5O4 spinel, especially in high rate applications.