Li-rich Materials Research Articles

Reversible anionic redox chemistry in layered Li4/7[□1/7Mn6/7]O2 enabled by stable Li–O-vacancy configuration

<h2>Summary</h2> The combination of anionic and cationic activities within Li-rich materials breaks through the traditional capacity limitation and achieves high-energy-density batteries. However, the utilization of anionic oxygen redox reactions always leads to detrimental lattice oxygen release, which accelerates structural distortion and electrochemical performance deterioration. In contrast to the typical Li–O–Li configuration in Li-rich layered oxides, not only can oxygen redox behaviors be triggered within layered Li_4/7[□_1/7Mn_6/7]O₂ (□: Mn vacancy) with Li–O-vacancy configuration, but lattice oxygen loss can be effectively suppressed. Upon Li⁺ (de)intercalations, Mn vacancy within the TM layer also enables reversible structural evolution and Li migration processes, further boosting high output capacity and long-term cycling stability. Besides, not only can the irreversible/reversible anionic/cationic redox reactions be clearly unraveled, but their capacity distributions can be roughly quantified upon cycling. Overall, our findings demonstrate that the introduction of Mn vacancy provides a promising configuration to achieve high-capacity cathode candidates for next-generation Li-ion batteries.

Another view of oxygen in cathodes for high energy batteries

The concept of utilizing anionic redox reactions to achieve high energy batteries has been revived for almost a decade by now; however, both its fundamental mechanism and practical implementation remain elusive and highly debated. In this issue of <i>Joule</i>, Weixin Song, Peter D. Nellist, and co-workers utilized electron ptychography to image the oxygen sublattice distortion of a Li-rich material that is known to involve oxygen redox reactions. Through the dose-efficient ptychography reconstruction with picometer resolution, they provide a beautiful demonstration of detecting the atomic placements of both the heavy, i.e., transition metals, and light, i.e., O and Li, elements of the Li-rich electrode at different electrochemical states, inspiring valuable discussions on the oxygen activities in battery cathodes.

Suppressing oxygen vacancies on the surface of Li-rich material as a high-energy cathode via high oxygen affinity Ca0.95Bi0.05MnO3 coating

Because of high energy density and work voltage, the Li-rich materials are considered to be one of the most promising next-generation lithium-ion batteries. However, the commercial applications are limited by the capacity loss, poor rate capability, and voltage decay during cycling. Herein, functionalizing the surface of Li1.2Mn0.54Ni0.13Co0.13O2 by Ca0.95Bi0.05MnO3 is proposed, which suppresses the formation of the oxygen vacancies and maintains structural stability by high oxygen affinity and alleviative electrolyte corrosion. Electrochemical tests demonstrate that this admirable electrode delivers excellent cycling stability. The Li-rich electrode decorated with 5 wt.% Ca0.95Bi0.05MnO3 exhibits a stable capacity retention of 86.5% at 0.1C after 200 cycles and an excellent full cell performance with the energy retention of 95.4% at 0.1C after 100 cycles. Moreover, the voltage decay of the modified material is restrained from 5.02 to 3.07 mV per cycle over 200 cycles. The finding here sheds new light on the development of the better Li-rich cathodes for improving electrochemical performance of electrode materials.

Tuning redox activity through delithiation induced protective layer and Fe-O coordination for Li-rich cathode with improved voltage and cycle performance

Li-rich layered transition metal oxides are one of the most promising cathode materials for their high energy density. However, the cathodes usually suffer from severe potential dropping and capacity fading during cycling, which are associated with the surface oxygen release and accompanied by cation densification and structural collapse. Herein, an integrative approach of simultaneous constructing uniform 3d Fe-ion doping in the transition metal layer and Li-rich Li5FeO4 shell to grab the oxygen and prevent interfacial side reactions is proposed. The introduction of Fe induces higher redox potential and stronger 3d Fe-O 2p covalent bond, triggering reversible anionic redox via a reductive coupling mechanism. And the delithiated product of Li-rich Li5FeO4 not only acts as a protective layer alleviating the side reactions but also enhances the surface kinetic property. With the benefit of promoted reversibility of oxygen redox and enhanced surface stability, the cathode exhibits high reversible capacity and superior cycle performance. Density function theory calculation indicates that the O 2p non-bonding state in the cathode incorporated with Fe sits at a lower energy band, resulting in higher energy storage voltage and improved oxygen stability. Consequently, the modified cathode exhibits a discharge specific capacity of 307 mA h g−1 (1C = 250 mA g−1), coulombic efficiency of 82.09% in the initial cycle at 0.1C and 88.34% capacity retention after 100 cycles at 1C. The work illustrates a strategy that could simultaneously enhance oxygen redox reversibility and interface stability by constructing lattice bond coordination and delithiation induced protective layer to develop Li-rich materials with high reversible capacity and long lifespan.

Modification Strategy for Constructing Li Gradient Combined with Spinel Phase Coating on Li-Rich Mn-Based Materials

Li-rich layered oxides (LLOs) are considered as the cathode materials for the next generation of lithium-ion batteries because of their high specific capacity. However, due to the structural rearrangement in the charging and discharging process, the initial Coulombic efficiency (ICE) is low and accompanied by serious voltage attenuation and bad cycle performance. In this work, the Li-gradient layer on the surface of the rod-like LLOs is constructed by the treatment of (NH4)2SiF6 under high temperature and subsequent washing. XRD, HRTEM, and Raman spectra verify the existence of the spinel phase of Li1–xMn2O4 on the surface of LLOs by the modification. The results of electrochemical measurements show that the modified LLOs exhibit a higher ICE of 87% with an excellent cycling retention of 90.4% (after 100 cycles at 1 C). These improvements on the electrochemical performance are caused by the high Li+ diffusion and improved the redox reversibility of oxygen ions on the LLOs with the unique structure of the Li-gradient and spinel coating layer on the surface.

Restriction of voltage decay by limiting low-voltage reduction in Li-rich oxide materials

Li-rich layered oxides are recognized as promising candidates for next-generation Li-ion batteries owing to the high capacity of >250 mAh g−1, but the severe voltage fade has prevented their commercialization. It is widely known that high-voltage charge processes result in layered-to-spinel structural evolution and voltage fade in Li-rich layered oxides. This work emphasizes that limiting the low-voltage reduction can maintain the structure and voltage stability of Li-rich layered oxides after the 4.6 V high-voltage charge processes. A strategy of limiting the low-voltage (<2.8 V) reduction by cycling at 4.6–2.8 V was performed in traditional Li1.2Ni0.13Mn0.54Co0.13O2 and high-Ni Li1.2Ni0.222Mn0.504Co0.074O2. After 300 cycles, traditional Li1.2Ni0.13Mn0.54Co0.13O2 and high-Ni Li1.2Ni0.222Mn0.504Co0.074O2 cycling at 4.6–2 V showed midpoint discharge voltages of 2.83 V and 2.97 V with high voltage fade rates of 2.25 mV/cycle and 2.24 mV/cycle, respectively. While the two materials cycling at 4.6–2.8 V can maintain discharge midpoint voltages of 3.34 V and 3.49 V, with low voltage decay rates of 0.692 mV/cycle and 0.632 mV/cycle, respectively. To better understand the voltage performance, their electric structures were calculated by density functional theory. Physical characterizations were also used to analyze their differences in structural evolution. The results suggested that limiting low-voltage reduction in Li-rich layered oxides is highly necessary for maintaining their structure and voltage stability.

Structural features of complete and partial activation of Li-rich cathodes studied by in-situ XRD

Li-rich oxides are materials shows a high specific discharge capacity which is achieved through a special charging procedure called activation. Still, these materials have the following disadvantages: a short cycle life and a drop of average discharge voltage. This paper describes the synthesis of Li1.2Ni0.13Co0.13Mn0.54O2 (LMR) and its 5 at.%. K doping (LMRK) by the sol-gel method. A capacity of the produced materials equals to 232 mAh/g for LMR and 228 mAh/g for LMRK, respectively, under 0.1 С discharge current. The criterion of Li2MnO3 phase complete activation was suggested following the results of studying charge/discharge curves and structural changes revealed with the use of in situ XRD method. This criterion has become a basis for determining the charge/discharge modes (current, voltage) required for Li2MnO3 phase complete activation. It has been found out that elevated current increases the voltage at which complete activation occurs. K doping affects the material diffusion characteristics and results in an extra increase in voltage at which complete activation occurs. The obtained results can be used to study the activation of Li-rich cathodic materials and to select the optimum operation mode of lithium-ion batteries manufactured with the use of such materials.

Improving the oxygen redox reversibility of Li-rich battery cathode materials via Coulombic repulsive interactions strategy

The oxygen redox reaction in lithium-rich layered oxide battery cathode materials generates extra capacity at high cell voltages (i.e., >4.5 V). However, the irreversible oxygen release causes transition metal (TM) dissolution, migration and cell voltage decay. To circumvent these issues, we introduce a strategy for tuning the Coulombic interactions in a model Li-rich positive electrode active material, i.e., Li1.2Mn0.6Ni0.2O2. In particular, we tune the Coulombic repulsive interactions to obtain an adaptable crystal structure that enables the reversible distortion of TMO6 octahedron and mitigates TM dissolution and migration. Moreover, this strategy hinders the irreversible release of oxygen and other parasitic reactions (e.g., electrolyte decomposition) commonly occurring at high voltages. When tested in non-aqueous coin cell configuration, the modified Li-rich cathode material, combined with a Li metal anode, enables a stable cell discharge capacity of about 240 mAh g−1 for 120 cycles at 50 mA g−1 and a slower voltage decay compared to the unmodified Li1.2Mn0.6Ni0.2O2.

Tracking the Fate of Excess Li in the Synthesis of Various Liy[Ni1−xMnx]O2 Positive Electrode Materials Under Different Atmospheres

Various Ni-rich Liy[Ni1−xMnx]O2 (x = ∼0.08, 0.2, 0.5) materials were synthesized with excess Li precursor in oxygen, dry air or air to understand what happens to the excess Li during synthesis. The Li[Ni1−xMnx]O2 components of the synthesized materials were single phase and synthesis in oxygen produced materials with less Ni in the Li layer. Inductively coupled plasma optical emission spectrometry (ICP-OES) and titration experiments on as-prepared samples and samples that were rinsed with water are useful in the determination of the amount of Li lost during heating, the amount of Li taken in by the material during synthesis and the amount of residual Li present in the samples as impurity phases. Materials synthesized in oxygen and dry air lost a similar amount of Li during heating but synthesis in air resulted in more Li loss. Synthesis in oxygen increased the lithium content, y, in the Liy[Ni1−xMnx]O2 materials. Materials with a higher Mn content can take in more Li to form Li-rich materials with larger values of y. From these experiments, the fate of Li can be tracked to heating loss, residual Li as impurity phases or uptake into the material as a function of Mn content and synthesis atmosphere.

Preparation of Li2MnO3 nanowires with structural defects as high rate and high capacity cathodes for lithium-ion batteries

Li2MnO3, as a member of Li-rich and Mn-rich (LMR) layered oxides, has been considered as an appealing candidate for cathode preparation due to its high capacity and high voltage. Nevertheless, its commercialized application has been hindered by its demerits of poor ratability and capacity decay. Meanwhile, structural defects have been proven to influence the electrochemical activities of Li2MnO3. Herein, Li2MnO3 nanowires with varying numbers of structural defects were prepared and measured as cathode materials. rLMO-2 nws with the highest level of oxygen vacancies and the largest amount of Mn3+ were found to exhibit higher specific capacities, higher capacity retention rates, and better rate performances. In order to demonstrate the superiority of nanowire materials with large surface areas, the performance of nanowires materials was compared with that of nanobelt materials. As LIB cathodes within the voltage window of 2.0–4.8 V and at the rate of 0.1C, R-LMO-30 nbs were found to reach the specific capacities of 98.7, 119.1, 137.7, and 146.8 mAh g−1 in the 2nd, 5th, 10th, and 20th cycles, respectively, while rLMO-2 nws delivered the relatively high values of 170.7, 189.4, 196.4, and 162.3 mAh g−1, respectively. The rLMO-2 nws sample also showed an enhanced rate capacity. The superior electrochemical properties of the rLMO-2 sample were associated with the nanowire structure’s large surface area, which could not only activate the Li2MnO3 phase quite easily but also enhance electron and ion transportation properties. This research revealed the influences of morphological control on the formation of surface structural defects in Li-rich layered oxides. And we believe our research findings will be helpful in providing a feasible strategy to enhance the electrochemical performance of Li-rich and Mn-rich layered oxides materials.

Theoretical insights into interfacial stability and ionic transport of Li2OHBr solid electrolyte for all-solid-state batteries.

Li-rich antiperovskite materials are promising candidates as inorganic solid electrolytes (ISEs) for all-solid-state Li-ion batteries (ASSLIBs). However, the material faces several pressing issues for its application, concerning the phase stability and electrochemical stability of the synthesized material and the Li-ion transport mechanism in it. Herein, we performed first-principles computational studies on the phase stability, interfacial stability, defect chemistry, and electronic/ionic transport properties of Li2OHBr material. The calculation results show that the Li2OHBr is thermodynamically metastable at 0 K and can be synthesized experimentally. This material exhibits a wider intrinsic electrochemical stability window (0.80-3.15 V) compared with sulfide solid electrolytes. Moreover, the Li2OHBr displays significant chemical stability when in contact with typical cathode materials (LiCoO2, LiMn2O4, LiFePO4) and moisture. The dominant defects of Li2OHBr are predicted to be VLi- and Lii +, corresponding to lower Li-ion migration barriers of 0.38 and 0.49 eV, respectively, while the replacement of some of the OH- by F- is shown to be effective in decreasing migration barriers in Li2OHBr. These findings provide a theoretical framework for further designing high performance ISEs.

Systematic study of the effects of lithium deficiencies on the crystal structure and electrochemical performance of Li-rich materials

A series of Li-rich materials with lithium deficiencies are obtained by a mild sol-gel and high-temperature calcination method. We use conventional test methods, such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy, to analyze the crystal structure and morphology of as-prepared materials. The results show that the Li1.1Mn0.54Co0.13Ni0.13O2 (named L1.1) displays superior electrochemical performance, that is, the discharge capacities are 303.9 and 145 mAh g−1 at rate of 0.1 C and 5 C, respectively. The excellent rate capability is mainly attributed to the formation of lithium vacancy and the formation of distorted lattice fringes, which enlarged the Li slab and changed the local structures in the L1.1 material.

Synchronous construction of oxygen vacancies with suitable concentrations and carbon coating on the surface of Li-rich layered oxide cathode materials by spray drying for Li-ion batteries

Lithium-rich layered oxide materials with high reversible capacities (over 250 mAh g−1) are considered as one of the most promising cathode materials for the next generation of lithium-ion batteries. However, some challenges including low initial Coulombic efficiency, voltage decay and poor cycling restrict their commercial application. Herrin, Li-rich layered oxide materials Li1.2Ni0.2Co0.08Mn0.52O2 co-modified by constructing oxygen vacancies with suitable concentration and C coating layer have been synthesized via a facile spray drying process. The oxygen vacancies with suitable concentration can not only suppress the release of O2 and improve the stability of the layered structure, but also facilitate Li diffusion. Moreover, C coating layer acts as a physical barrier to protect the materials from electrolyte, and reduce the interface impedance. The co-modified material shows excellent electrochemical properties: a high initial Coulombic efficiency of 83.1%, a small voltage decay rate of 0.306 mV, and a capacity retention of 78.3% after 1000 cycles at 5 C. And it provides a simple and feasible way to improve the properties of lithium-rich layered oxide materials.

Cobalt Free Structurally Integrated Positive Electrode Materials for Lithium-Ion Batteries

Introduction Rechargeable Lithium-ion batteries (LIBs) having high energy density have been widely used as energy storage device for electric vehicles (EVs) and hybrid-electric vehicles (HEVs). It is necessary to increase the energy density of LIBs in order to meet future energy requirements. Since energy density depends mainly on positive electrodes, exploration of new positive electrode materials with high specific capacities, good rate capabilities and cycling stabilities become crucial.In this context, positive electrodes, which are composites of Li-rich layered materials (high specific capacity) and spinel materials (high rate capability) attracted intense attention. Li-rich layered positive electrode materials deliver a capacity of ~250 mAh g-1 when charged above 4.5 V[1]. A large irreversible initial capacity is observed, which is attributed to the complete electrochemical activation of Li2MnO3 with the simultaneous removal of oxygen and lithium (“Li2O”) from the crystal lattice[1]. Further, this class of materials exhibits poor rate capability[2]. Spinel-type positive electrodes are marked by its high operating voltage (4.7 V), good cycling stability as well as high rate capability due to the fast Li+ diffusion through its three-dimensional structure, even though it offers a low discharge capacity (about 140 mAh g-1)[4]. Additionally, Fe substitution to the spinel positive electrode materials was found to be effective in improving thermal stability, structural stability as well as electrochemical performance[5]. Further, Fe is cost-effective and is earth abundant[3]. Results and Discussion In the present work, Fe–containing cobalt free structurally integrated (at molecular level) Li-rich layered-spinel positive electrode material was synthesized by sol-gel method. Four different annealing temperatures were selected to get final products. The structure and morphology of the materials were characterized by using X-ray diffraction (XRD) and Field emission scanning electron microscopy (FESEM). X-ray diffraction (XRD) studies showed that obtained composite materials contain spinel (space group Fd-3m) as well as Li-rich layered phases (space group C2/m). Mössbauer spectroscopy experiments revealed the coordination environment and oxidation state of the Fe present in the composite. Furthermore, the electrochemical performance was investigated within the voltage range 2.00 - 4.95 V vs. Li+/Li. The obtained cyclic voltammograms further confirmed the coexistence of Li-rich layered and spinel components in the composites. Selected materials delivered high discharge capacity, close to 200 mAh g-1 and ˃ 90% capacity retention after 50 cycles and will be discussed in detail. Acknowledgement: A.Bhaskar and H. Enale acknowledge the financial support from funding agency, Science and Engineering Board (SERB), New Delhi, India through ECR/2017/002556 program. D. Dixon acknowledges the financial support from funding agency, Science and Engineering Board (SERB), New Delhi, India through Ramanujan Fellowship, under the grant number SB/S2/ RJN-162/2017. A. Surendran is grateful to UGC New Delhi (Ref. no.:63/CSIR-UGC NET DEC. 2017) for the UGC SRF grant and Academy of Scientific and Innovative Research (AcSIR), Ghaziabad- 201002, India. The CIF, CSIR-CECRI is acknowledged for technical support with material characterization. A. Thottungal acknowledges the Council of Scientific and Industrial Research (CSIR) for a senior research fellowship.

Ti Substitution in Li5FeO4: A Li-Rich Cathode Material for Li-Ion Batteries from First Principles Calculations

Li-rich materials with simultaneous anionic and cationic reductions are one among the most promising class of cathode materials for high−capacity Li-ion batteries. The recent studies on the Li-rich Li5FeO4 with defect antifluorite-type structure show that Li5FeO4 can generate high capacity by simultaneous reduction of Fe and O atoms without any obvious release of oxygen gas. But, the poor cyclability as well as electrical conductivity of Li5FeO4 makes it a less attractive cathode for Li-ion batteries in practical applications. In the present study, we have substituted the Fe sites with Ti in different concentrations (Li5Fe1−x Ti x O4 with x = 0.125, 0.250, 0.375, 0.500, 0.625, 0.750, 0.875, 1.00) and investigated the structural, electronic and Li-diffusion properties using density functional theory calculations. The total energy calculations show that all the Ti substituted systems have negative enthalpy of formation and this implies that the Ti substituted materials are also stable. The analysis of the calculated density of states indicates that Ti substitution reduces the bandgap and thereby improves the electronic conductivity of these materials. Similarly, the analysis of Li migration in Ti substituted Li5FeO4 shows lower barrier height compared to that in the parent compound indicating the possibility of fast diffusion of Li-ions by Ti substitution.

A synergistic exploitation to produce high-voltage quasi-solid-state lithium metal batteries

The current Li-based battery technology is limited in terms of energy contents. Therefore, several approaches are considered to improve the energy density of these energy storage devices. Here, we report the combination of a heteroatom-based gel polymer electrolyte with a hybrid cathode comprising of a Li-rich oxide active material and graphite conductive agent to produce a high-energy “shuttle-relay” Li metal battery, where additional capacity is generated from the electrolyte’s anion shuttling at high voltages. The gel polymer electrolyte, prepared via in situ polymerization in an all-fluorinated electrolyte, shows adequate ionic conductivity (around 2 mS cm−1 at 25 °C), oxidation stability (up to 5.5 V vs Li/Li+), compatibility with Li metal and safety aspects (i.e., non-flammability). The polymeric electrolyte allows for a reversible insertion of hexafluorophosphate anions into the conductive graphite (i.e., dual-ion mechanism) after the removal of Li ions from Li-rich oxide (i.e., rocking-chair mechanism).

Understanding Li roles in chemical reversibility of O2-type Li-rich layered cathode materials

Traditional O3-type Li-rich layered materials are attractive with ultra-high specific capacities, but suffering from inherent problems of voltage hysteresis and poor cycle performance. As an alternative, O2-type materials show the potential to improve the oxygen redox reversibility and structural stability. However, their structure-performance relationship is still unclear. Here, we investigate the correlation between the Li component and dynamic chemical reversibility of O2-type Li-rich materials. By exploring the formation mechanism of a series of materials prepared by Na/Li exchange, we reveal that insufficient Li leads to an incomplete replacement, and the residual Na in the Li-layer would hinder the fast diffusion of Li+. Moreover, excessive Li induces the extraction of interlayer Li during the melting chemical reaction stage, resulting in a reduction in the valence of Mn, which leads to a severe Jahn-Teller effect. Structural detection confirms that the regulation of Li can improve the cycle stability of Li-rich materials and suppress the trend of voltage fading. The reversible phase evolution observed in in-situ X-ray diffraction confirms the excellent structural stability of the optimized material, which is conducive to capacity retention. This work highlights the significance of modulating dynamic electrochemical performance through the intrinsic structure.

Study on electrochemical performance of Al-substitution for different cations in Li-rich Mn-based materials

Layered Li-rich Mn-based cathode materials have attracted immense interest for using in lithium-ion batteries, owing to their high energy density. However, the severe degradation of cycle and rate performances has impeded the actual commercial application. Herein, Al was selected as doping element to substitute for the metal elements of Li, Ni, Co and Mn in Li1.2Mn0.54Ni0.13Co0.13O2 material to promote electrochemical performances and optimize element proportion. Results indicate that when replacing Li with Al, it displays outstanding initial coulombic efficiency of 80.06%. Besides, Al-substitution for Co shows excellent rate performance of 147.3 mAh g−1 at 5.0 C. Particularly, the replacement of Mn not only shows the highest capacity and voltage retention within the potential range from 2.0 to 4.8 V, but also presents superior capacity retention up to the potential of 5.0 V. Unfortunately, the substitution of Ni displays the worst balanced electrochemical performance among Al-doped materials, which shows lower voltage retention than that of pristine. The reasons why Al-substitution for various cations displays difference on electrochemical performance were discussed from the perspective of migration, dissolution and valence reduction of transition metal ions to the structure evolution in detail. The proposed method and detected action mechanisms can provide guidance on how to optimize materials structure and composition for cathode materials in lithium-ion batteries to obtain electrode materials with excellent comprehensive electrochemical performance.

Microstructure-Controlled Li-Rich Mn-Based Cathodes by a Gas–Solid Interface Reaction for Tackling the Continuous Activation of Li2MnO3

Li-rich Mn-based cathodes have attracted much attention due to their high capacity stemming from anion redox above 4.5 V. However, the continuous activation of Li2MnO3 in Li-rich Mn-based materials, which correlates with O2 release and TM migration, is usually unfavorable to structural stability. Herein, based on a gas-solid interface reaction, we tackle this continuous activation phenomenon by restricting the capacity release of Li2MnO3 via NH4HCO3 treatment in the Li1.2Ni0.36Mn0.44O2 cathode. After modification, oxygen vacancies associated with the spinel phase are introduced on the surface. The 4 mol % NH4HCO3-modified material's capacity starts at 182 mAh g-1 at 1 C instead of increasing from 173 to 186 mAh g-1 for 25 cycles in the pristine material. Meanwhile, it also exhibits an excellent capacity retention of 93.24% after 200 cycles (at 1 C), with a small voltage decay rate of 1.19 mV cycle-1.

Critical Role of Ti4+ in Stabilizing High-Voltage Redox Reactions in Li-Rich Layered Material.

Li-rich layered oxide materials are considered promising candidates for high-capacity cathodes for battery applications and improving the reversibility of the anionic redox reaction is the key to exploiting the full capacity of these materials. However, permanent structural change of the electrode occurring upon electrochemical cycling results in capacity and voltage decay. In view of these factors, Ti4+ -substituted Li2 IrO3 (Li2 Ir0.75 Ti0.25 O3 ) is synthesized, which undergoes an oxygen redox reaction with suppressed voltage decay, yielding improved electrochemical performance and good capacity retention. It is shown that the increased bond covalency upon Ti4+ substitution results in structural stability, tuning the phase stability from O3 to O1' upon de-lithiation during charging compared with O3 to T3 and O1 for pristine Li2 IrO3 , thereby facilitating the oxidation of oxygen. This work unravels the role of Ti4+ in stabilizing the cathode framework, providing insight for a fundamental design approach for advanced Li-rich layered oxide battery materials.