Synthesis and Characterization of a Multication Doped Mn Spinel, LiNi0.3_{0.3}Cu0.1_{0.1}Fe0.2_{0.2}Mn1.4_{1.4}O4_{4}, as 5 V Positive Electrode Material

The suitability of multication doping to stabilize the disordered Fd3̅m structure in a spinel is reported here. In this work, LiNi$_{0.3}$Cu$_{0.1}$Fe$_{0.2}$Mn$_{1.4}$O$_{4}$ was synthesized via a sol–gel route at a calcination temperature of 850 °C. LiNi$_{0.3}$Cu$_{0.1}$Fe$_{0.2}$Mn$_{1.4}$O$_{4}$ is evaluated as positive electrode material in a voltage range between 3.5 and 5.3 V (vs Li$^{+}$/Li) with an initial specific discharge capacity of 126 mAh g$^{-1}$ at a rate of C/2. This material shows good cycling stability with a capacity retention of 89% after 200 cycles and an excellent rate capability with the discharge capacity reaching 78 mAh g$^{-1}$ at a rate of 20C. In operando X-ray diffraction (XRD) measurements with a laboratory X-ray source between 3.5 and 5.3 V at a rate of C/10 reveal that the (de)lithiation occurs via a solid-solution mechanism where a local variation of lithium content is observed. A simplified estimation based on the in operando XRD analysis suggests that around 17–31 mAh g$^{-1}$ of discharge capacity in the first cycle is used for a reductive parasitic reaction, hindering a full lithiation of the positive electrode at the end of the first discharge

A method to prolong lithium-ion battery life during the full life cycle

Extended lifetime of lithium-ion batteries decreases economic costs and environmental burdens in achieving sustainable development. Cycle life tests are conducted on 18650-type commercial batteries, exhibiting nonlinear and inconsistent degradation. The accelerated fade dispersion is proposed to be triggered by the evolution of an additional potential of the anode during cycling as measured vs. Li$^+$/Li. A method to prolong the battery cycle lifetime is proposed, in which the lower cutoff voltage is raised to 3 V when the battery reaches a capacity degradation threshold. The results demonstrate a 38.1% increase in throughput at 70% of their beginning of life (BoL) capacity. The method is applied to two other types of lithium-ion batteries. A cycle lifetime extension of 16.7% and 33.7% is achieved at 70% of their BoL capacity, respectively. The proposed method enables lithium-ion batteries to provide long service time, cost savings, and environmental relief while facilitating suitable second-use applications

Constructing a Thin Disordered Self‐Protective Layer on the LiNiO₂ Primary Particles Against Oxygen Release

One of the major challenges facing the application of layered LiNiO2 (LNO) cathode materials is the oxygen release upon electrochemical cycling. Here it is shown that tailoring the provided lithium content during synthesis process can create a disordered layered Li1-xNi1+xO2 phase at the primary particle surface. The disordered surface, which serves as a self-protective layer to alleviate the oxygen loss, possesses the same layered rhombohedral structure (R m) as the inner core of primary particles of the Li1-xNi1+xO2 (x ≈ 0). With advanced synchrotron-based x-ray 3D imaging and spectroscopic techniques, a macroporous architecture within the agglomerates of LNO with ordered surface (LNO-OS) is revealed after only 40 cycles, concomitant with the reduction of nickel on the primary particle surface throughout the whole secondary particles. Such chemomechanical degradation accelerates the deterioration of LNO-OS cathodes. Comparably, there are only slight changes in the nickel valence state and interior architecture of LNO with a thin disordered surface layer (LNO-DS) after cycling, mainly arising from an improved robustness of the oxygen framework on the surface. More importantly, the disordered surface can suppress the detrimental H2 ⇋ H3 phase transition upon cycling compared to the ordered one

Kinetic Control of Long‐Range Cationic Ordering in the Synthesis of Layered Ni‐Rich Oxides

Deciphering the sophisticated interplay between thermodynamics and kinetics of high‐temperature lithiation reaction is fundamentally significant for designing and preparing cathode materials. Here, the formation pathway of Ni‐rich layered ordered LiNi$_{0.6}$Co$_{0.2}$Mn$_{0.2}$O$_{2}$ (O‐LNCM622O) is carefully characterized using in situ synchrotron radiation diffraction. A fast nonequilibrium phase transition from the reactants to a metastable disordered Li$_{1−x}$(Ni$_{0.6}$Co$_{0.2}$Mn$_{0.2}$)$_{1+x}$O$_2$ (D‐LNCM622O, 0 < x < 0.95) takes place while lithium/oxygen is incorporated during heating before the generation of the equilibrium phase (O‐LNCM622O). The time evolution of the lattice parameters for layered nonstoichiometric D‐LNCM622O is well‐fitted to a model of first‐order disorder‐to‐order transition. The long‐range cation disordering parameter, Li/TM (TM = Ni, Co, Mn) ion exchange, decreases exponentially and finally reaches a steady‐state as a function of heating time at selected temperatures. The dominant kinetic pathways revealed here will be instrumental in achieving high‐performance cathode materials. Importantly, the O‐LNCM622O tends to form the D‐LNCM622O with Li/O loss above 850 °C. In situ XRD results exhibit that the long‐range cationic (dis)ordering in the Ni‐rich cathodes could affect the structural evolution during cycling and thus their electrochemical properties. These insights may open a new avenue for the kinetic control of the synthesis of advanced electrode materials

In Situ X-ray Diffraction and X-ray Absorption Spectroscopic Studies of a Lithium-Rich Layered Positive Electrode Material: Comparison of Composite and Core–Shell Structures

Lithium- and manganese-rich transition-metal oxide (LMR-NMC) electrodes have been designed either as heterostructures of the primary components (“composite”) or as core–shell structures with improved electrochemistry reported for both configurations when compared with their primary components. A detailed electrochemical and structural investigation of the 0.5Li2MnO3–0.5LiNi0.5Mn0.3Co0.2O2 composite and core–shell structured positive electrode materials is reported. The core–shell material shows better overall electrochemical performance compared to its corresponding composite material. While both configurations gave the same initial charge capacity of ∼300 mAh/g when cycled at a rate of 10 mA/g at 25 °C, the core–shell sample gives a discharge capacity of 232 mAh/g compared to 208 mAh/g delivered by the composite sample. Also, the core–shell sample gave better rate capability and a smaller first-cycle irreversible capacity loss than the composite sample. The improved performance of the core–shell material is attributed to its lower surface reactivity and limited structural change since the more stable Li2MnO3 shell screens the more reactive Ni-rich core material from interacting with either air or electrolyte at high potentials, thereby preventing electrode surface modification. In situ X-ray diffraction correlated with electrochemical data revealed that the composite sample shows stronger volumetric changes in the lattice parameters during charging to 4.8 V. In addition, X-ray absorption spectroscopy showed an incomplete Ni reduction process after the first discharge for the composite sample. From these results, it was shown that this leads to a more severe degradation in the composite material that affects Li+ intercalation in the subsequent discharge, thereby resulting in its poorer performance. Furthermore, to confirm these results, another LMR-NMC material with a different composition (having a Ni-poor core)—0.5Li2MnO3-0.5LiNi0.33Mn0.33Co0.33O2—was investigated. The core–shell structured positive electrode material also gave an improved electrochemical performance compared to the corresponding composite positive electrode material. These results show that the core–shell configuration could effectively be used to improve the performance of the LMR-NMC materials to enable future high-energy applications

The structural origin of enhanced stability of Na3.32Fe2.106Ca0.234(P2O7)2Na_{3.32}Fe_{2.106}Ca_{0.234}(P_{2}O_{7})_{2} cathode for Na-ion batteries

The storage of renewable energy depends largely on sustainable technologies such as sodium-ion batteries with high safety, long lifespan, low cost, and non-toxicity. Pyrophosphate Na$_{3.32}$Fe$_{2.34}$(P$_2$O$_7$)$_2$ cathode could meet this requirement, however, its structural stability needs to be further enhanced for practical purposes. To overcome this problem, Na-deficient Na$_{3.32}$Fe$_{2.11}$Ca$_{0.23}$(P$_2$O$_7$)$_2$ with exceptional stability is prepared by Ca selective doping in this work. In operando synchrotron-based X-ray diffraction (SXRD) and in situ X-ray absorption near edge spectroscopy (XANES) results reveal that the prepared Na$_{3.32}$Fe$_{2.11}$Ca$_{0.23}$(P$_2$O$_7$)$_2$ is a single-phase solid-solution reaction with high reversibility. A strong correlation between the voltage curve and lattice parameters is deciphered for the first time. Additionally, the atomic-doping-engineering strategy could significantly enhance the thermal and electrochemical stability of the electrode materials, contributing to their good structural reversibility and enhanced operational safety. Specifically, after 1000 cycles at 1 C, the Ca doped electrode achieves a high capacity retention of 81.7%, which is much better than that of the un-doped electrode (15.5%). Our work may pave a new avenue for designing safe and low-cost cathode materials for battery applications with long cycle life

Li+/Na+Li^{+}/Na^{+} Ion Exchange in Layered Na2/3(Ni0.25Mn0.75)O2Na_{2/3}(Ni_{0.25}Mn_{0.75})O_{2}: A Simple and Fast Way to Synthesize O3/O2-Type Layered Oxides

Normally, high temperatures are required for solid-state reactions to overcome energy barriers in the formation of lithium insertion materials. Consequently, conventional high-temperature lithiation reactions are very time- and energy-consuming and often accompanied by undesirable side reactions. Thus, how to synthesize Li-containing cathode materials with a desired structure under a short reaction time and low temperature is of paramount significance. Herein, layered sodium-deficient Na$_{2/3}$□$_{1/3}$(Ni$_{0.25}$Mn$_{0.75}$)O$_2$ (□ for vacancy) oxides with different oxygen stackings (P2 or P3 structure) were deployed in lithium ion batteries. An interesting Li$^+$/Na$^+$ ion-exchange reaction between the electrode material and LiPF6-based carbonate electrolyte was observed at room temperature for the first time. Such a reaction can produce the layered Li$_{2/3}$□$_{1/3}$(Ni$_{0.25}$Mn$_{0.75}$)O$_2$ compounds having the O2 or O3 structure, which show the ability to reversibly accommodate lithium ions over a relatively wide voltage range. Our experiments may open up a pathway toward the development of novel electrode materials

Constructing a Thin Disordered Self‐Protective Layer on the LiNiO2_2 Primary Particles Against Oxygen Release

One of the major challenges facing the application of layered LiNiO$_2$ (LNO) cathode materials is the oxygen release upon electrochemical cycling. Here it is shown that tailoring the provided lithium content during synthesis process can create a disordered layered Li$_{1-x}$Ni$_{1+x}$O$_2$ phase at the primary particle surface. The disordered surface, which serves as a self-protective layer to alleviate the oxygen loss, possesses the same layered rhombohedral structure (R$\bar{3}$m) as the inner core of primary particles of the Li$_{1-x}$Ni$_{1+x}$O$_2$ (x ≈ 0). With advanced synchrotron-based x-ray 3D imaging and spectroscopic techniques, a macroporous architecture within the agglomerates of LNO with ordered surface (LNO-OS) is revealed after only 40 cycles, concomitant with the reduction of nickel on the primary particle surface throughout the whole secondary particles. Such chemomechanical degradation accelerates the deterioration of LNO-OS cathodes. Comparably, there are only slight changes in the nickel valence state and interior architecture of LNO with a thin disordered surface layer (LNO-DS) after cycling, mainly arising from an improved robustness of the oxygen framework on the surface. More importantly, the disordered surface can suppress the detrimental H2 ⇋ H3 phase transition upon cycling compared to the ordered one