LiCoO2 Electrode Research Articles

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.

Analysis of LiCoO2 electrodes through principal component analysis of current–voltage datacubes measured using atomic force microscopy

This study aimed to reveal the electrical characteristics of the composite electrodes of Li-ion batteries. LiCoO2 electrodes were analyzed using atomic force microscopy, and three-dimensional datasets of current–voltage (I–V) curves (IV-datacubes) were obtained. The IV-datacubes were then analyzed using principal component analysis to determine the typical I–V curve corresponding to each LiCoO2 particle on a statistical basis. Detailed analysis based on the thermionic emission model with series resistance showed that some of the particles exhibited poor electrical contact in the electrode. Overall, the obtained results suggested that our IV-datacube analysis can reveal the characteristics of buried electrical contacts within electrodes, which is otherwise difficult to accomplish using alternative methods. We, therefore, believe that the method presented herein is a promising analytical method for composite electrodes.

Ionic liquid additive stabilized cathode/electrolyte interface in LiCoO2 based solid-state lithium metal batteries

Poly(ethylene oxide) (PEO)-based solid state batteries is one of the most attractive candidates for next-generation high performance energy storage devices, especially when it matches the LiCoO2 cathode of high volumetric energy density. However, cathode/electrolyte interface reactions will be triggered at high voltage, leading to high interfacial resistance and fast capacity decay. In this work, a selected ionic liquid, 1-methyl-1-propylpiperidinium tetrafluoroborate (PP13BF4), is prepared and applied in LiCoO2 electrode operating at high work voltages of 3.0–4.3 V to regulate the interface. Electrochemical impedance spectroscopy and holding test indicate that facilitated by the PP13BF4, the cathode/electrolyte interfacial reaction is effectively suppressed and the resistance is reduced. When an optimal content, 2 wt%, PP13BF4 is added into the LiCoO2 electrode, the solid-state lithium metal cell delivers an initial discharge capacity of 125.1 mAh g−1 under the current density of 0.05 C at 55 °C, which is almost twice that of bare electrode. Meantime, it retains 76.3% of its capacity in 100 cycles under 0.2 C rate. Further characterizations illustrate that PP13BF4 participates in the formation of a protective CEI, which effectively suppresses parasitic reactions between electrolyte and electrode. This work provides a facile and practical idea for the development of 4 V class solid state lithium metal batteries.

All-Solid-State Three-Electrode Cells with Reduced Li4Ti5O12 Reference Electrode

Introduction All-solid-state lithium-ion batteries (ASS-LIBs) are expected as next-generation LIBs because of high safety standard and power characteristics. However, ASS-LIBs still have several problems, such as short cycle life and high mass ratio of solid electrolytes. In order to solve these problems, it is necessary to clarify operation mechanisms of ASS-LIBs. In this study, we focused on electrochemical measurements, which have high versatility and high time resolution. Although three-electrode cells have been used in the electrochemical measurements of conventional LIBs to clarify the behavior of single electrodes, there have been few reports on three-electrode cells in ASS systems. [1] Moreover, electrochemical impedance spectroscopy (EIS) with three-electrode cells has never been reported in ASS-LIB systems. Thus, we synthesized chemically reduced Li4Ti5O12 (R-LTO) as an active material of the reference electrode and fabricated ASS three-electrode cells, and investigated electrochemical properties of LiCoO2 (LCO) composite electrode in Li-In|Li10GeP2S12(LGPS)|LCO cells by charge/discharge measurements and EIS measurements. Experimental methods R-LTO powder was synthesized by mixing of white Li4Ti5O12 powder with a tetrahydrofuran solution of lithium-naphthalenide. R-LTO reference electrode was fabricated by coating of the slurry composed of bluish black R-LTO powder, N-methyl-2-pyrrolidone and polyvinylidene fluoride on a nickel mesh current-collector. ASS three-electrode cell consisted of LCO composite electrode (LiNbO3-coated LCO:LGPS=7:3 wt%) as the working electrode, R-LTO reference electrode, LGPS as the solid electrolyte, and Li-In alloy as the counter electrode. Electrochemical measurements were carried out with a multichannel electrochemical system (VSP-300, Biologic). Results and Discussion Charge/discharge curves of the LCO electrodes and Li-In electrodes showed plateaus at around 2.35 V and –0.95 V vs. R-LTO, respectively. Assuming that the redox potential of Li7Ti5O12/ Li4Ti5O12 is 1.55 V vs. Li/Li+, we can calculate the plateau potentials of the LCO and Li-In electrodes to be 3.90 V and 0.60 V vs. Li/Li+, respectively. This clearly shows that the R-LTO reference electrodes successfully worked as an LTO redox couple. In the EIS measurements, the impedances of the LCO and the Li-In were successfully separated with the three-electrode cells since the impedance measured without the reference electrode agreed well with the combined impedance from those of the LCO and Li-In electrodes, which were separately measured with the reference electrode. We also investigated the temperature dependence and the state-of-charge (SOC) dependence of the LCO impedance. Figure 1 (a) shows the Nyquist plots obtained at 273, 288 and 298 K, and Figure 1 (b) gives the Arrhenius plots of two resistance values, R 2 and R 3, calculated with the equivalent circuit shown in the inset of Fig. 1 (a). The activation energy of R 3 was calculated to be 37 kJ mol–1, which is similar to that of the charge transfer resistance of LCO reported in ASS systems [2,3]. In addition, the SOC dependence of R 3 was similar to that of the charge transfer resistance observed for LCO electrode in a liquid electrolyte system [4]. From these results, R 3 can be assign to the charge transfer resistance. The activation energy of R 2 was 57 kJ mol–1, which is much higher than that of ionic conductivity of LGPS and also inconsistent with that of LCO electronic conductivity. Considering the SOC independence of R 2, we can assign R 2 to some interface or interphase resistance in the composite electrodes. The data with other electrode materials will be also reported in the presentation.

Analysis of Mechanical Properties of Composite Electrode with Different Binder Molecular Weights

In order to improve the energy density of the lithium ion battery, the loading level of the electrode is continuously increasing. As a result, the presence of inactive materials such as conductive materials / binders in the electrodes is also highlighted. In particular, securing the mechanical properties of the electrode according to the distribution and composition of the binder is becoming more important in terms of long-term reliability. However, increasing the composition of the binder of the electrode can ensure the mechanical properties of the electrode at the same loading level and density, but increases the resistance of the electrode. This increase in resistance may reduce the lifetime of the electrode, apart from the mechanical properties of the electrode. Therefore, in order to minimize the resistance increase rate of the electrode and to secure mechanical properties, the mechanical properties and resistance of the electrode according to the molecular weight of the binder in the electrode were analyzed.In this presentation, three LiCoO2 electrodes with different PVDF binder molecular weights of 500,000 / 630,000 / 1,000,000 were prepared, and the adhesion and volume resistivity of the electrodes were measured using SAICAS and Electrode Resistance Meter. Although the adhesion of the electrodes was different according to the molecular weight of the PVdF binder, the increase in the volume resistivity of the electrode was not large. This is because the behavior of the binder and the active material / conductive material in the electrode are different from each other as the molecular weight of the binder increases, and the mechanical properties of the binder are also different according to the molecular weight. In order to confirm this more intuitively, the battery was fabricated and the behavior of the electrode was observed. Furthermore, the physical properties of the polymer were analyzed according to the molecular weight of the binder in order to clarify the cause.

Interface Structure and Transport Properties of Thin-Film Solid-State Batteries with an Epitaxial Cathode

A problem of solid-state Li ion batteries is a relatively low ionic conductivity at the interface between electrodes and electrolytes that limits the charging/discharging rate. For designing the solid-state batteries, understanding the mechanism behind the low interface conductivity is crucial. Investigation of the atomic structure of the interfaces and its relation to the ionic conductivity would be helpful for this purpose. However, atomic-scale observation of the buried interfaces is often difficult in practical batteries which consist of grain aggregates. Recent progress in thin-film deposition techniques of electrodes and electrolyteshas opened a path to study the interface quantitatively. By using an all-in-vacuum battery fabrication system [1], we succeeded in fabricating a very low solid-electrolyte/electrode interface resistance in thin film batteries with an epitaxial cathode. The well-defined crystalline interfaces allow the analysis of atomic-scale structure and its transport properties. For the structure analysis, we used X-ray crystal truncation rod (CTR) scattering which enables the atomic-scale analysis in a non-destructive manner.The analysis of two interfaces will be presented: a solid-electrolyte/electrode interface and an electrode/current collector interface. In the former case, we studied Li(negative electrode)/Li3PO4(solid electrode)/LiCoO2(positive electrode) thin-film Li batteries with low and high (more than 10 times) interface resistances. It turned out that the low-resistance interface has an atomically well-ordered LiCoO2 surface and a disordered surface CoO2 layer can results in the high-resistance interface, demonstrating the crucial importance of the structural ordering in the interfacial layer for realizing a low-resistance interface [2]. In the second topic, we focused on electrode/current collector interface that can also affect the battery performance. We found a drastic improvement of the charging/discharging property by inserting 1.2 nm-thick band insulator LaAlO3 into the LiCoO2 (electrode)/Nb-doped SrTiO3 (current collector) interface. The CTR analysis revealed that a formation of electric dipole at the LaAlO3/Nb-doped SrTiO3 interface, which causes a energy band alignment preferable for the electronic conductance between the electrode and the current collector.

Electrochemical Relithiation for Direct Regeneration of LiCoO2 Materials from Spent Lithium-Ion Battery Electrodes

Increased generation of spent lithium-ion batteries (LIBs) has driven the exploration of new methods for reusing and/or recycling LiCoO₂ cathode materials. Herein, an electrochemical relithiation method was proposed to directly regenerate LiCoO₂ cathode materials using the waste LiₓCoO₂ electrode as a base. It was shown that Li⁺ was successfully inserted into the waste LiₓCoO₂ electrode, and this relithiation process became faster with either a higher Li₂SO₄ concentration or a higher cathodic current density. The XRD analysis confirmed that the peak positions of the relithiation products were consistently close to those of a standard LiCoO₂ material. The crystal structure of the relithiation products was restored with a post-annealing process. The activation energy for electrochemical relithiation (Eₐ) was estimated at 22 kJ mol–¹, and the constant of equilibrium constant k₀ was determined as 1.35 × 10–⁶ cm s–¹. The relithiation process was controlled by the charge transfer process when the Li₂SO₄ concentration was high (e.g., 1, 0.8, and 0.5M), and a lower concentration at 0.01–0.3 M led to a diffusion control pattern. The electrode made of the regenerated LiCoO₂ materials had a charge capacity of 136 mAh g–¹, close to that of the commercial LiCoO₂ electrode (140 mAh g–¹). A potential mechanism of electrochemical relithiation was proposed involving lithium defects, relithiation, and crystal regeneration.

The aluminum current collector with honeycomb-like surface and thick Al2O3 film increased durability and enhanced safety for lithium-ion batteries

Durability and safety are main factors contributing to the market requirement of lithium-ion batteries (LIBs) in practical applications. The improvement of current collector has been proven as an effective approach to enhance comprehensive performance of LIBs. To achieve a sufficient electrical contact between the current collector and active materials, honeycomb-like surface of aluminum current collector is etched by direct current in sulfuric acid and phosphoric acid mixed solution. At the same time, a dense anodic aluminum oxide film is formed on the surface of aluminum current collector, which can protect LIBs from corrosion and thermal runaway. Experimental results show that the adhesion between the active material and aluminum current collector was improved by 23% after anodization. The corrosion resistance of alumina foil was promoted significantly in ethyl methyl carbonate and ethylene carbonate electrolyte with LiPF6. The corrosion current peak reduces to 0.022 mA/cm2 from 0.267 mA/cm2 after surface treatment. The capacity retention rate of the LiCoO2 electrode with an oxidation-treated aluminum current collector is 6.3% higher than with untreated aluminum foil at 5C after 500 cycles. What’s more, the nail penetration demonstrates that the aluminum current collector we prepared can reduce the temperature of the full batteries surface when the nail pierced, which improved the safety performance of LIBs.

Evolution of the morphology, structural and thermal stability of LiCoO2 during overcharge

The overcharge behaviors of 1000 mAh LiCoO2/graphite pouch cells are systematically investigated through the analysis of morphology, structural and thermal stability of LiCoO2 under different state of charge (SOC) of 120%, 150%, 174%, 190% and 220%. The LiCoO2 experiences the phase transition from O3 to H1-3 and then O1 together with the grain breakage and boundary slip as evidenced by XRD and SEM analysis respectively, which results in the pronounced Co dissolution after the SOC of 174%. The impedance analysis of the pouch cells and coin cells demonstrates that the main contribution of impedance increase originates from the LiCoO2 electrode. Under the combined effect of structural collapse, Co dissolution, and electrolyte oxidization, the thermal stability of LiCoO2 cathode materials reduces with the progressing of overcharge as revealed by differential scanning calorimetry (DSC) results. We hope that this comprehensive understanding can provide meaningful guidance for advancing the overcharge performance of LiCoO2/graphite pouch cells.

Engineering lithium-ion battery cathodes for high-voltage applications using electromagnetic excitation

Microwave radiation (MWR), a type of electromagnetic excitation source, reduces the synthesis temperature and processing time for chemical reactions compared to traditional synthesis methods. Recently, we demonstrated that MWR can engineer ceramics with different crystal phases compared to traditional methods [Journal of Materials Chemistry A5, 35 (2017)]. In this study, we further apply the MWR-assisted technique to improve the electrochemical performance of LiCoO2 cathodes by engineering TiO2 and ZrO2 ceramic coatings. Electrochemical tests suggest that the TiO2 coating improves the rate capability of the LiCoO2 electrode. Both TiO2 and ZrO2 coatings improve the high-voltage (4.5 V) cycling stability of LiCoO2. The capacity remaining is improved from 52.8 to 84.4% and 81.9% by the TiO2 coating and the ZrO2 coating, respectively, after 40 cycles. We compare these results with existing studies that apply traditional methods to engineer TiO2/ZrO2 on LiCoO2, and find that the MWR-assisted method shows better performance improvement. X-ray photoelectron spectroscopy measurements suggest that the improved cycling stability arises from the formation of metal fluorides that protect the electrode from side reactions with electrolytes. This mechanism is further supported by the reduced Co dissolution from TiO2/ZrO2-coated LiCoO2 electrode after cycling. This study provides a new toolbox facilitating the integration of many delicate, low melting point materials like polymers into battery electrodes.

Performance of Li4Ti5O12-based reference electrode for the electrochemical analysis of all-solid-state lithium-ion batteries

The establishment of three-electrode cells for all-solid-state lithium-ion batteries is an important issue to clarify the electrochemical behavior of the battery components and solve problems for the practical applications. Here we prepared an all-solid-state three-electrode cell with a chemically-reduced Li4Ti5O12 reference electrode and investigated electrochemical properties of a LiCoO2 composite electrode in a Li-In|Li10GeP2S12|LiCoO2 cell. Plateau potentials in charge-discharge curves were coincident with reported values. Cell impedance measured with two-electrode configuration agreed well with the sum of the impedances of the positive and the negative electrodes measured with the reference electrode. These results show that chemically-reduced Li4Ti5O12 reference electrode was worked as a Li7Ti5O12|Li4Ti5O12 reference electrode and electrochemical properties of the LiCoO2 electrode and the Li-In electrode were separated. From the temperature and the state of charge dependences of LiCoO2 impedance, resistances related to interface or interphase and charge-transfer reaction were identified. These results show that all-solid-state cells with chemically-reduced Li4Ti5O12 reference electrodes are promising candidates for three-electrode cells for all-solid-state lithium-ion battery systems.

Tailoring Solution-Processable Li Argyrodites Li6+xP1-xMxS5I (M = Ge, Sn) and Their Microstructural Evolution Revealed by Cryo-TEM for All-Solid-State Batteries.

Owing to their high Li+ conductivities, mechanical sinterability, and solution processability, sulfide Li argyrodites have attracted much attention as enablers in the development of high-performance all-solid-state batteries with practicability. However, solution-processable Li argyrodites have been developed only for a composition of Li6PS5X (X = Cl, Br, I) with insufficiently high Li+ conductivities (∼10-4 S cm-1). Herein, we report the highest Li+ conductivity of 0.54 mS cm-1 at 30 °C (Li6.5P0.5Ge0.5S5I) for solution-processable iodine-based Li argyrodites. A comparative investigation of three iodine-based argyrodites of unsubstituted and Ge- and Sn-substituted solution-processed Li6PS5I with varied heat-treatment temperature elucidates the effect of microstructural evolution on Li+ conductivity. Notably, local nanostructures consisting of argyrodite nanocrystallites in solution-processed Li6.5P0.5Ge0.5S5I have been directly captured by cryogenic transmission electron microscopy, which is a first for sulfide solid electrolyte materials. Specifically, the promising electrochemical performances of all-solid-state batteries at 30 °C employing LiCoO2 electrodes tailored by the infiltration of Li6.5P0.5Ge0.5S5I-ethanol solutions are successfully demonstrated.

Improvement of float charge durability for LiCoO2 electrodes under high voltage and storage temperature by suppressing O1-Phase transition

To produce electronic devices with high functionality and longer operating times, the energy density of lithium-ion batteries (LIBs) has to be increased while maintaining a long battery life and high reliability. The energy density of LIBs can be increased by increasing the charge cut-off voltage. The float charge durability of LIBs containing LiCoO2 under high voltage is one of the most important issues in practical use. The leakage current during float charge conditions is caused by the O1 phase transition of LiCoO2. In this study, metal-substituted lithium cobalt oxides, LiCo1-xMxO2 (M = Co, Ni, Al, Mg, and Zr), were investigated to suppress degradation during float charge conditions. When Ni was substituted for Co at an amount of 5%, the float charge durability improved more than 4 times compared to bare-LiCoO2 without lowering the energy density. According to the structural analysis, we proposed the mechanism for improving float charge durability by LiCo1-xNixO2; Ni ions partially migrate to the lithium layer and then stabilize the O3 structure. This Ni ions substitution in LiCoO2 greatly contributes to extending life and the safety of high energy density LIBs containing layered positive materials.

Reaction uniformity visualized by Raman imaging in the composite electrode layers of all-solid-state lithium batteries.

The reaction uniformity of LiCoO2 composite positive electrodes in all-solid-state cells was compared quantitatively by investigating the Raman band shifts corresponding to the state-of-charge (SOC) of LiCoO2. The quantitative SOC analysis was conducted using the Raman imaging data of composite electrodes with smaller or larger solid electrolytes. The electrodes exhibited different reaction uniformity although the cells showed similar initial charge capacities and average SOC. In the case of larger solid electrolytes, most LiCoO2 particles showed higher or lower SOC than the average SOC, and lower battery performance. The quantitative analysis of SOC in each LiCoO2 electrode demonstrated that a variable SOC outside the average SOC resulted in larger irreversible capacity and lower rate performance. The quantitative SOC analysis newly developed in the present study is a useful technique for designing composite electrodes showing higher battery performance.

Structural elucidation of the degradation mechanism of nickel-rich layered cathodes during high-voltage cycling.

Phase transition occurring during cycling plays a fundamentally important role in the cycling performance of nickel-rich cathodes. Here, splitting of two O3 phases, rather than the often observed O1 phases in the conventional LiCoO2 electrode, was discovered in LiNi0.85Co0.10Mn0.05O2 at a high-voltage region (>4.6 V). Such degradation could be mitigated via Al doping.

Investigation of the cathodic interfacial stability of a nitrile electrolyte and its performance with a high-voltage LiCoO2 cathode.

The limited discharge capacity of LiCoO2 can be improved by increasing its working potential, but it suffers from Co4+ dissolution and decomposition of the electrolyte. Nitriles have attracted great interest as high-voltage electrolytes due to their wide electrochemical window. However, the cathodic interfacial stability of nitrile electrolytes with a high-voltage LiCoO2 cathode has yet to be explored. Herein, we adopted an SN-based deep eutectic electrolyte with SN as the only solvent and found that Co4+ could be reduced by the SN solvent on the interface of the LiCoO2 electrode, causing a reverse phase change of LiCoO2 and severe self-discharge of the LiCoO2|Li and LiCoO2|Li4Ti5O12 batteries. When LiDFOB was introduced into the electrolyte, the self-discharge behavior of cells could be largely decelerated. The series of characterizations performed in our work revealed that the cathode/electrolyte interface generated from the LiDFOB salt could stabilize the interface of LiCoO2 and suppress the dissolution of the ions of the transition metal Co.

Effects of a solid electrolyte coating on the discharge kinetics of a LiCoO2 electrode: mechanism and potential applications

The application of a Li+-conductive amorphous Li2B4O7 coating on a LiCoO2 electrode enhanced its discharge kinetics by increasing the local concentration of Li+ at the surface of LiCoO2 particles.

Recovery Li/Co from spent LiCoO2 electrode based on an aqueous dual-ion lithium-air battery

While lithium-ion batteries dominate the field of electronic devices and vehicles, recovery of LiCoO2 from spent batteries becomes a significant process. Aqueous lithium-air battery and dual-ion battery were blended into a novel electrochemical system as dual-ion lithium-air battery (DLAB) system to recover Li and Co elements from the spent LiCoO2 (acid solution). In the system, oxygen, LiCoO2 acid solution and Li2Ti2(PO4)3 (LTPO), which has Na+ superionic conductor structure and is synthesized by sol-gel method, were used as cathode, dual-ion electrolyte and anode. Relatively low voltage plateaus, stability and insolubility of LTPO make it to be a feasible candidate for this aqueous DLAB. By applying Pt/C as a catalyst for cathode, the full discharged system exhibits a Co ion recovering rate of up to 96.2%. Moreover, this system presents positive discharge plateaus at around 0.47 V and 0.10 V during recovering, demonstrating an output energy density of 43.88 Wh kg−1. The system shows a green and promising way for the recovery of spent LiCoO2 battery.

Mechanical robustness of composite electrode for lithium ion battery: Insight into entanglement & crystallinity of polymeric binder

To investigate the correlation between the molecular weight of the polymeric binder in Li-ion battery electrodes and their adhesion properties, polyvinylidene fluoride (PVdF) with three different molecular weights of 500,000, 630,000, and 1,000,000 are selected for LiCoO2 electrode fabrication. Using a surface and interfacial cutting analysis system, it is observed that, as the molecular weight of the PVdF increases, the adhesion strength not only in the electrode composite, but also at the electrode/current collector interface increases. This enhancement can be attributed to the increased polymeric chain entanglement and higher crystallinity of PVdF with higher molecular weight, which is confirmed using a microfluidic viscometer and differential scanning calorimeter, respectively. In summary, regardless of slightly higher electrode resistance, the LiCoO2 electrode with a PVdF binder of high molecular weight shows better electrochemical performance during cycling test even at 60 °C due to its stable mechanical integrity.

Structural Distortion-Induced Charge Gradient Distribution of Co Ions in Delithiated LiCoO2 Cathode.

Layered LiCoO2 has drawn tremendous attention as a modeling cathode for Li-ion batteries, while its structural instability, especially in the high delithiation region, remains unsolved. With the aim of revealing the structural fundamentals, LiCoO2 electrodes are investigated at a long delithiation range using both in situ and ex situ techniques. In the highly delithiated LiCoO2 electrode, the unique charge compensation process leads to a spatial charge gradient of Co2+/Co3+/Co4+ ions from surface to bulk, which can be further manipulated by structural distortion, Li extraction, and surface side reactions. The coordinated surface oxygen is shown to be electrochemically active and fully reversible in participating in the charge compensation during cycling. Moreover, the active lattice O can be significantly stabilized by introducing the undesired surface Li-Co antisites, which also play an effective role in accommodating the internal stress induced by volume changes. These findings effectively bridge the structural changes with the Li+/e- migration kinetics to elucidate the degradation of LiCoO2 cathode upon delithiation, demonstrating a rewarding avenue for improving the electrochemical performance of LiCoO2 itself and developing high energy density cathodes for the battery community as well.