High-voltage LiCoO2 Research Articles

High-entropy doping for high-voltage LiCoO2 with enhanced electrochemical performances

Lithium cobalt oxide (LiCoO2), as a pioneering layered oxide cathode material for lithium-ion batteries (LIBs), possesses exceptional theoretical specific capacity and cycling stability, positioning it as a leading candidate for commercial LIB applications. Boosting the upper-limit of charge voltage of LiCoO2 is a promising strategy to increase the capacity of batteries, vital for advancing energy storage solutions from portable electronics to electric vehicles. Nevertheless, hybrid redox reactions at high voltages speed up oxygen evolution, electrolyte decomposition, and irreversible phase transitions, ultimately causing rapid capacity fading.To address these challenges, we present a novel approach to enhance the structural stability and electrochemical performances of LiCoO2 cathode via La-Al-Mg-Y high-entropy doping. This strategy significantly improves the high-voltage cycling stability of the cathode material by retaining 72.5 % of its initial capacity after 500 cycles at 5 C under 4.6 V. Furthermore, the structural change caused by the phase transition between the O3 and H1-3 phases is remarkably suppressed. This advancement in LIB cathode technology paves the way for the development of high performance batteries and it is crucial for meeting the growing demand for sustainable energy storage.

Surface Engineering via Rare Earth Oxide Composite Coating to Enhance the High-Voltage Stability of the LiCoO2 Cathode.

The commercial application of high-voltage LiCoO2 (LCO) faces significant challenges due to rapid capacity decay, primarily attributed to an unstable interface and structure at deeply delithiated states. Herein, a unique rare earth oxide composite coating comprising La2O3, Y2O3, and LaYO3 has been prepared to stabilize LCO at high voltage. The synergistic effect between these rare earth oxides significantly reinforces the protective capabilities of the coating, effectively enhancing the interfacial/structural stability of LCO. When tested at 4.6 V, the coated LCO exhibits an excellent capacity retention of 94.4% after 300 cycles at 1 C. Even after an ultralong charge/discharge test of 700 cycles at 2 C, the coated LCO retains 85.2% of its initial specific capacity, which significantly outperforms the uncoated LCO (6.3%). Moreover, the coated LCO shows enhanced cycling performance at a high temperature of 45 °C, owing to the outstanding thermal stability of the La-Y-O composite. Additionally, the superior cycling stability of the coated LCO at 4.7 V, compared to the uncoated LCO, demonstrated the promising potential of the La-Y-O composite coating in improving electrochemical performance of LCO at higher cutoff voltages. These findings highlight an efficacious strategy to enhance the interfacial/structural stability of high-voltage LCO using rare earth oxides.

Ionic-conductive poly (vinylidene fluoride) polymer as a versatile binder to stabilize high-voltage LiCoO2 cathode materials

Ionic-conductive poly (vinylidene fluoride) polymer as a versatile binder to stabilize high-voltage LiCoO2 cathode materials

Al Impurity Upcycled High-Voltage Cathodes from Spent LiCoO2 Batteries.

Al impurity is among the most likely components to enter the spent lithium-ion battery (LIB) cathode powder due to the strong adhesion between the cathode material and the Al current collector. However, high-value metal elements tend to be lost during the deep removal of Al impurities to obtain high-purity metal salt products in the conventional hydrometallurgical process. In this work, the harmful Al impurity is designed as a beneficial ingredient to upcycle high-voltage LiCoO2 by incorporating robust Al-O covalent bonds into the bulk of the cathode assisted with Ti modification. Benefiting from the strong Al-O and Ti-O bonds in the bulk, the irreversible phase transitions of the upcycled R-LCO-AT have been significantly suppressed at high voltages, as revealed by in situ XRD. Moreover, a Li+-conductive Li2TiO3 protective layer is constructed on the surface of R-LCO-AT by pinning slow-diffusion Ti on the grain boundaries, resulting in improved Li+ diffusion kinetics and restrained interface side reactions. Consequently, the cycle stability and rate performance of R-LCO-AT were significantly enhanced at a high cutoff voltage of 4.6 V, with a discharge capacity of 189.5 mAhg-1 at 1 C and capacity retention of 92.9% over 100 cycles at 4.6 V. This study utilizes the detrimental impurity element to upcycle high-voltage LCO cathodes through an elaborate bulk/surface structural design, offering a strategy for the high-value utilization of spent LIBs.

Scalable Precise Nanofilm Coating and Gradient Al Doping Enable Stable Battery Cycling of LiCoO2 at 4.7 V.

The quest for smart electronics with higher energy densities has intensified the development of high-voltage LiCoO2 (LCO). Despite their potential, LCO materials operating at 4.7 V faces critical challenges, including interface degradation and structural collapse. Herein, we propose a collective surface architecture through precise nanofilm coating and doping that combines an ultra-thin LiAlO2 coating layer and gradient doping of Al. This architecture not only mitigates side reactions, but also improves the Li+ migration kinetics on the LCO surface. Meanwhile, gradient doping of Al inhibited the severe lattice distortion caused by the irreversible phase transition of O3-H1-3-O1, thereby enhanced the electrochemical stability of LCO during 4.7 V cycling. DFT calculations further revealed that our approach significantly boosts the electronic conductivity. As a result, the modified LCO exhibited an outstanding reversible capacity of 230 mAh g-1 at 4.7 V, which is approximately 28 % higher than the conventional capacity at 4.5 V. To demonstrate their practical application, our cathode structure shows improved stability in full pouch cell configuration under high operating voltage. LCO exhibited an excellent cycling stability, retaining 82.33 % after 1000 cycles at 4.5 V. This multifunctional surface modification strategy offers a viable pathway for the practical application of LCO materials, setting a new standard for the development of high-energy-density and long-lasting electrode materials.

Practical surface-reconstruction strategy based on self-reactive interface design enables ultralong cyclability of commercial cathodes for lithium-ion batteries

Although Al-doped high-voltage LiCoO2 (HVLCO) cathode has been widely used in commercial lithium-ion batteries, it still suffers from poor cycling stability due to its unstable surface/interface structure causing bad side reactions. Herein, a surface reconstruction strategy based on self-reactive interface design has been proposed, to construct a uniform and ultrathin (∼ 5 nm) LiAlO2 (LAO) layer on the surface of HVLCO cathodes. The construction of LAO layer is realized by a facile and scalable process involving chemical immersion in LiOH solution and subsequent heating treatment. Moreover, the LAO coating layer imparts both lower interior stress upon lithiation and lower migration energy barrier of Li ions, guaranteeing stable and rapid lithium storage, which is confirmed by substantial characterizations and theory calculations. Consequently, ultralong cycle life over 10,000 h (1000 cycles) at 0.1 C is achieved for the surface-reconstructed HVLCO cathode, with an 86% capacity retention. Especially, different kinds of commercial HVLCO products as well as NCM (LiNi0.6Co0.2Mn0.2O2) cathode material, after the same surface reconstruction, also show remarkably reinforced electrochemical performance. This practical surface-reconstruction strategy may serve as a useful guideline for future design and performance optimization of commercial cathode materials.

New Insight into Bulk Structural Degradation of High-Voltage LiCoO2 at 4.55 V.

The aggravated mechanical and structural degradation of layered oxide cathode materials upon high-voltage charging invariably causes fast capacity fading, but the underlying degradation mechanisms remain elusive. Here we report a new type of mechanical degradation through the formation of a kink band in a Mg and Ti co-doped LiCoO2 cathode charged to 4.55 V (vs Li/Li+). The local stress accommodated by the kink band can impede crack propagation, improving the structural integrity in a highly delithiated state. Additionally, machine-learning-aided atomic-resolution imaging reveals that the formation of kink bands is often accompanied by the transformation from the O3 to O1 phase, which is energetically favorable as demonstrated by first-principles calculations. Our results provide new insights into the mechanical degradation mechanism of high-voltage LiCoO2 and the coupling between electrochemically triggered mechanical failures and structural transition, which may provide valuable guidance for enhancing the electrochemical performance of high-voltage layered oxide cathode materials for lithium-ion batteries.

Constructing stable electrode–electrolyte interfaces by sulfone-based additive to improve the high-voltage performance of LiCoO2

LiCoO2 battery can provide high reversible capacity at a high voltage of 4.6 V, however, maintaining its stability at high voltages remains a major challenge. To address this issue, ethyl methyl sulfone (EMS) is employed as an electrolyte additive to construct stable interfaces between the electrode and electrolyte under high-voltage condition. The characterization results indicate that the addition of EMS can inhibit the decomposition of the standard electrolyte (STD) and the dissolution of Co2+ from cathode, as well as the formation of lithium dendrites on the Li anode, thereby enhancing the stability of both cathode/electrolyte and anode/electrolyte interfaces. Consequently, the cycling performance of LiCoO2 battery using STD+3 %EMS is augmented by 16.9 % at 1 C under a cut-off voltage of 4.6 V over 100 cycles, delivering a specific capacity of 137 mA h g−1. This research provides novel insights into the design of electrolyte additives for high-voltage LiCoO2 batteries and contributes to the further development of high-voltage lithium-ion batteries.

High-Performance Dendrite-Free Lithium Metal Anode Based on Metal-Organic Framework Glass.

The performance of lithium metal batteries is severely hampered by uncontrollable dendrite growth and volume change within the anode. This work addresses these obstacles by introducing a novel strategy: applying an isotropic and internal grain-boundary-free layer, specifically, a metal-organic framework (MOF) glass layer with nano-porosity onto the electrochemically plated lithium metal anode. Both ab initio and classical molecular dynamics simulations indicate that the MOF glass layer makes the lithium transport smooth and uniform via its internal monolithic and interfacial advantages. This MOF glass layer with the fast and more uniform lithium diffusion in the monolithic interior and its interface enables dendrite-free lithium plating and stripping through surface confinement effect and interfacial effect. When employed in symmetric batteries, the achieved Li metal anode can operate over 300h at 1mAcm-2. The full batteries matched with LiFePO4 exhibit high capacity (148mAhg-1), excellent rate performance (61mAhg-1 at 5C), and outstanding cycling stability (with capacity retention of ≈90% after 1000 cycles). The full batteries matched with high-voltage LiCoO2 also show superior performances. Therefore, the strategy of utilizing a MOF glass layer enables the development of high-performance lithium metal anodes.

Gradient fluorination engineering through interdiffusion reaction for high-voltage LiCoO2

The advancement of high charging cut-off voltage stands as a crucial avenue to enhance the energy density of LiCoO2 (LCO). However, LCO faces severe interface and bulk phase issues at high voltage (≥ 4.6 V), resulting in poor cycling stability. In this study, we reconstruct the surface structure of LCO based on the interdiffusion reaction between LCO and MgF2 in a high-temperature sintering process. Specifically, this interdiffusion reaction yields an ultra-thin LiF coating layer, artificially reinforcing the chemical structure of the cathode-electrolyte interphase (CEI) during cycling. This LiF-rich CEI not only effectively protects the surface structure of LCO, but also facilitates the lithium-ion diffusion. Furthermore, the diffusion of F and Mg into the LCO lattice significantly strengthens the structure, which inhibits unfavorable phase transitions from the O3 phase to the H1–3 phase at high voltage. Consequently, such modified LCO with concurrently enhanced interface and bulk structure exhibits outstanding long-term cycling performance within 3.0–4.6 V at 1 C, achieving a capacity retention of 84.9 % after 1000 cycles. Meanwhile, it also demonstrates excellent high-temperature performance, with a capacity retention of 85.0 % after 200 cycles under 45 °C.

Anion-mediated interphase construction enabling high-voltage solid-state lithium metal batteries

Enhancing the interphase stability of polymer electrolytes with high-voltage cathodes is crucial for the development of high-energy-density lithium metal batteries (LMBs), especially in wearable devices area. Herein, lithium difluorophosphate (LiDFP) is incorporated into the solid polymer electrolyte of poly(ethylene oxide) (PEO) to enhance the formation of a robust cathode-electrolyte interphase (CEI) in high-voltage LiCoO2 LMBs. Through combining electrochemical measurements, spectroscopic techniques and theoretical calculations, the underlying modification mechanism is revealed. Due to its stronger anionic coordination with both polymer electrolyte chain and proton, and more oxidation-active resultant anion-coordinated polymer compared with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), LiDFP suppresses the formation of the strong acid HTFSI deriving from the deprotonated process of the terminal O-H group thus avoiding the further oxidative attack to the polymeric framework. Furthermore, under the synergetic decomposition of HDFP intermediate, the polymer-derived radical helps to reconstruct a chemo-mechanically stable and Li-conductive CEI layer, which consists of abundant LiF/Li3PO4/LixPOyFz inorganic species distributed in lithiated organic macromolecules. The in-situ constructed CEI effectively passivates catalytic sites on LiCoO2 directly against PEO, resulting in well-maintained layered structure during high-voltage cycling. The proposed interphasial chemistry that regulates CEI formation provides directive knowledge of electrolyte optimization for high-voltage solid-state batteries.

In Situ Polymerized Quasi-Solid Electrolytes Compounded with Ionic Liquid Empowering Long-Life Cycling of 4.45 V Lithium-Metal Battery.

High-voltage resistant quasi-solid-state polymer electrolytes (QSPEs) are promising for enhancing the energy density of lithium-metal batteries in practice. However, side reactions occurring at the interfaces between the anodes or cathodes and QSPEs considerably reduce the lifespan of high-voltage LMBs. In this study, a copolymer of vinyl ethylene carbonate (VEC) and poly(ethylene glycol) diacrylate (PEGDA) was used as the framework, with a cellulose membrane (CE) as the supporting layer. Based on density functional theory calculations, 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI), an ionic liquid, was screened because of its lowest unoccupied molecular orbital energy level as a modifying agent for the in situ P(VECx-EGy)/Pyrz/LiTFSI@CE QSPEs synthesis. Pyr14+, with a lithiophobic alkyl chain, forms a dense positive ion shielding layer on the protruding tips of deposited lithium, facilitating uniform and smooth lithium deposition. Pyr14TFSI assists in constructing a stable solid electrolyte interphase (SEI) layer on the Li surface enriched with LiF, Li3N, and RCOOLi. The modulation of lithium deposition behavior on the anode by Pyr14TFSI ensures stable Li plating/stripping for >1500 h. A Li-Cu cell exhibits stable cycling for >200 cycles at a current density of 0.05 mA cm-2, with an average Coulombic efficiency of 92.7%. In situ polymerization ensures that P(VECx-EGy)/Pyrz/LiTFSI@CE QSPEs exhibit excellent interface compatibility with the anode and the cathode. The CR2032 button cell Li|P(VEC1-EG0.06)/Pyr0.4/LiTFSI@CE|LiCoO2 demonstrates stable cycling with a negligible capacity decay of 0.083% per cycle for >390 cycles at 25 °C and 0.2 C when using a high-voltage LiCoO2 (4.45 V) cathode. Furthermore, a 7.1 mAh pouch cell achieves stable charge-discharge cycles, confirming the pronounced stability of the as-fabricated QSPE at the interfaces of the high-voltage LiCoO2 cathode and Li anode.

Selective core-shell doping enabling high performance 4.6 V-LiCoO2

Constructing robust surface and bulk structure is the prerequisite for realizing high performance high voltage LiCoO2 (LCO). Herein, we manage to synthesize a surface Mg-doping and bulk Al-doping core-shell structured LCO, which demonstrates excellent cycling performance. Half-cell shows 94.2% capacity retention after 100 cycles at 3.0–4.6 V (vs. Li/Li+) cycling, and no capacity decay after 300 cycles for full-cell test (3.0–4.55 V). Based on comprehensive microanalysis and theoretical calculations, the degradation mechanisms and doping effects are systematically revealed. For the undoped LCO, high voltage cycling induces severe interfacial and bulk degradations, where cracks, stripe defects, fatigue H2 phase, and spinel phase are identified in grain bulk. For the doped LCO, Mg-doped surface shell can suppress the interfacial degradations, which not only stabilizes the surface structure by forming a thin rock-salt layer but also significantly improves the electronic conductivity, thus enabling superior rate performance. Bulk Al-doping can suppress the lattice “breathing” effect and the detrimental H3 to H1-3 phase transition, which minimizes the internal strain and defects growth, maintaining the layered structure after prolonged cycling. Combining theoretical calculations, this work deepens our understanding of the doping effects of Mg and Al, which is valuable in guiding the future material design of high voltage LCO.

Hybrid ion/electron interfacial regulation stabilizes the cobalt/oxygen redox of ultrahigh-voltage lithium cobalt oxide for fast-charging cyclability

High-voltage and fast-charging LiCoO2 (LCO) is key to high-energy/power-density Li-ion batteries. However, unstable surface structure and unfavorable electronic/ionic conductivity severely hinder its high-voltage fast-charging cyclability. Here, we construct a Li/Na-B-Mg-Si-O-F-rich mixed ion/electron interface network on the 4.65 V LCO electrode to enhance its rate capability and long-term cycling stability. Specifically, the resulting artificial hybrid conductive network enhances the reversible conversion of Co3+/4+/O2−/n− redox by the interfacial ion–electron cooperation and suppresses interface side reactions, inducing an ultrathin yet compact cathode electrolyte interphase. Simultaneously, the derived near-surface Na+/Mg2+/Si4+-pillared local intercalation structure greatly promotes the Li+ diffusion around the 4.55 V phase transition and stabilizes the cathode interface. Finally, excellent 3 C (1 C = 274 mA g−1) fast charging performance is demonstrated with 73.8% capacity retention over 1000 cycles. Our findings shed new insights to the fundamental mechanism of interfacial ion/electron synergy in stabilizing and enhancing fast-charging cathode materials.

Construction of Uniform LiF Coating Layers for Stable High-Voltage LiCoO2 Cathodes in Lithium-Ion Batteries.

Stabilizing LiCoO2 (LCO) at 4.5 V rather than the common 4.2 V is important for the high specific capacity. In this study, we developed a simple and efficient way to improve the stability of LiCoO2 at high voltages. After a simple sol-gel method, we introduced trifluoroacetic acid (TA) to the surface of LCO via an afterwards calcination. Meanwhile, the TA reacted with residual lithium on the surface of LCO, further leading to the formation of uniform LiF nanoshells. The LiF nanoshells could effectively restrict the interfacial side reaction, hinder the transition metal dissolution and thus achieve a stable cathode-electrolyte interface at high working-voltages. As a result, the LCO@LiF demonstrated a much superior cycling stability with a capacity retention ratio of 83.54% after 100 cycles compared with the bare ones (43.3% for capacity retention), as well as high rate performances. Notably, LiF coating layers endow LCO with excellent high-temperature performances and outstanding full-cell performances. This work provides a simple and effective way to prepare stable LCO materials working at a high voltage.

Multifunctional Umbrella: In Situ Interface Film Forming on the High-Voltage LiCoO2 Cathode by a Tiny Amount of Nanoporous Polymer Additives for High-Energy-Density Li-Ion Batteries.

The LiCoO2 (LCO) cathode is foreseen for extensive commercial applications owing to its high specific capacity and stability. Therefore, there is considerable interest in further enhancing its specific capacity by increasing the charging voltage. However, single-crystal LCO suffers from a significant capacity degradation when charged to 4.5V due to the irreversible phase transition and unstable structure. Herein, an ultra-small amount (0.5%wt. in the electrode) of multi-functional PIM-1 (a polymer with intrinsic microporosity) additive is utilized to prepare a kind of binder-free electrode. PIM-1 modulates the solvation structure of LiPF6 due to its unique structure, which helps to form a stable, robust, and inorganic-rich cathod-eelectrolyte interphase (CEI) film on the surface of LCO at a high voltage of 4.5V. This reduces the irreversible phase transition of LCO, thereby enhancing the cyclic stability and improving the rate performance, providing new perspectives for the electrodes fabrication and improving LCO-based high-energy-density cathodes.

Mitigation of charge heterogeneity by uniform in situ coating enables stable cycling of LiCoO2 at 4.6V

LiCoO2 is a predominant cathode for lithium-ion batteries of portable electronics owing to its merit of high volumetric energy density. Nevertheless, it experiences rapid capacity deterioration under high voltages, concomitant with structural degradation and numerous intragranular cracks. Coating has been recognized as an efficacious strategy to ameliorate the decline in cycling performance of LiCoO2 at high voltages. Hence, a systematic elucidation of the precise mechanisms underlying the mitigation of structural degradation via coating layers assumes paramount importance in the context of advancing the next generation of high-voltage LiCoO2. In this work, the intricate interrelation among lithium-ion diffusion coefficients, charge heterogeneity, and crack distribution is explicated through techniques inclusive of galvanostatic intermittent titration technique (GITT), finite element analysis (FEA), and X-ray computed tomography (XCT). A robustly stable lithium-ion-conducting coating material serves the function of curtailing the occurrence of surface passivation layers, achieved by diminishing side reactions between the LiCoO2 and the electrolyte; while a uniform coating ensures a homogeneous lithium-ion flux, thereby mitigating charge heterogeneity and the resultant mechanical strain as well as intragranular cracks. Both are important elements that collectively allow the coating to effectively protect the surface from structural degradation, thus achieving superior performances upon high-voltage charging.

Ferroelectric BaTiO3 Regulating the Local Electric Field for Interfacial Stability in Solid-State Lithium Metal Batteries.

Solid-state Li metal batteries (SSLMBs) are widely investigated since they possess promising energy density and high safety. However, the poor interfacial compatibility between the electrolyte and electrodes limits their promising development. Herein, a robust composite electrolyte (poly(vinyl ethylene carbonate) electrolyte with 3 wt % of BaTiO3, PVEC-3BTO) with excellent interfacial performance is rationally designed by incorporating ferroelectric BaTiO3 (BTO) nanoparticles into the poly(vinyl ethylene carbonate) (PVEC) electrolyte matrix. Benefiting from the high dielectric constant and ferroelectric properties of BTO, the interfacial compatibility between electrolytes and electrodes was significantly improved. The enhanced Li+ transference number (0.64) of solid electrolyte and in situ generated BaF2 inorganic interphase contribute to the enhanced cycling stability of PVEC-3BTO based Li//Li symmetrical batteries. Furthermore, the antioxidation ability of PVEC-3BTO has also been enhanced by modulating the local electric field for good pairing with high-voltage LiCoO2 material. Therefore, in this work, the mechanism of BTO for improving interfacial compatibility is revealed, and also useful methods for addressing the interface issues of SSLMBs have been provided.

Understanding the role of TiO2 coating for stabilizing 4.6V high-voltage LiCoO2 cathode materials

TiO2 surface coating is considered to be an effective strategy for improving the cycling performance of commercially available high voltage LiCoO2 (HV-LCO) batteries. However, the mechanism underlying the TiO2 coating remains ambiguous due to the synergy of solid-state coating and annealing processes. In this work, the effects of TiO2 were systematically studied for 4.6 V HV-LCO batteries. The results showed that the coated TiO2 can be transformed into LiTiO2-rich layer, which can reduce surface residual lithium (SRL), lower the formation of Co3O4 and LiF-rich cathode electrolyte interphase (CEI) layer. Moreover, the annealed sample delivered improved surface texture, reduced specific surface area, and lower SRL, which was beneficial to improve the rate capability and cyclic performance. However, the LCO after annealing and coating exhibited weak static oxygen stability at high voltage due to the change in bulk Li/Co stoichiometry, leading to higher gas production. This work provides new insights into the effects of metal oxide coating and sheds light on the commercial process for HV-LCO.

Tannic acid mediated coating of Al-Ti-oxide nanolayer on LiCoO2 cathode for high-voltage lithium-ion batteries

High-voltage LiCoO2 (LCO) satisfies the demand of high-energy lithium-ion batteries, but suffers adverse factors including structural irreversibility, micro-crack formation, active material erosion and electrode/electrolyte side reactions, which limits its electrochemical performance beyond 4.2 V. Here, we employed a surface coating method based on tannic acid (TA) pretreatment to vary the properties of LCO surface. The TA-mediated Al-Ti oxide (ATO) coating on LCO resulted in the interface doping of Al3+ and Ti4+ as well as the spinel phase transition layer, which inhibited the surface degradation and the structural instability. As a result, the obtained PLCO@ATO0.5% maintained 112 mAh g−1 after 600 cycles with a high voltage of 4.5 V. It also exhibited capacity retention of 80% after 100 cycles at 45 °C and the rate performance of 155 mAh g−1 at 10 C.