Li3V2(PO4)3-coated Li1.17Ni0.2Co0.05Mn0.58O2 as the cathode materials with high rate capability for Lithium ion batteries

Improving the long-term electrochemical performances of Li-rich cathode material by encapsulating a three-in-one nanolayer

With large specific capacity, wide voltage window, and high energy density, Li-rich layered oxides have been considered as a promising cathode candidate for advanced lithium-ion batteries (LIBs). However, their commercial application is challenging due to severe capacity degradation and voltage fading caused by irreversible oxygen evolution and phase transition upon repeated cycling. This work proposes an effective strategy to improve the long-term electrochemical performances of Li_1.2Mn_0.56Ni_0.17Co_0.07O₂ (LMNCO) by constructing multifunctional nanolayers composed of element-doping, layered-spinel heterostructural connection, and fast ion conductor shell via a facile method. The Li_0.09B_0.97PO₄ (LBPO) coating shell acts as a fast ion carrier and physical screen to promote Li⁺ diffusion and isolate side reactions at the cathode-electrolyte interface; moreover, two-phase transitional region provides three-dimensional channel to facilitate Li⁺ transport and inhibit phase transition. Besides, B³⁺ and PO₄^3--doping collaborates with oxygen vacancies to stabilize lattice oxygen and restrain oxygen evolution from the bulk active cathode. The optimized LMNCO@LBPO material exhibits a superior capacity retention of 78.6%, higher than that of the pristine sample (49.3%), with the mitigated voltage fading of 0.73 mV per cycle after 500 cycles at 1 C. This study opens up an avenue for the surface modification to the electrochemical properties and perspective application of Li-rich cathodes in high-performance LIBs.

Enhancing Cell Performance of Lithium-Rich Manganese-Based Materials via Tailoring Crystalline States of a Coating Layer

Li-rich Mn-based-layered oxides are considered to be the most felicitous cathode material candidates for commercial application of lithium-ion batteries on account of high energy density. Nevertheless, defects containing an unsatisfactory initial Coulombic efficiency and rapid voltage decay seriously impede their practical utilization. Herein, a coating layer with three distinct crystalline states are employed as a coating layer to modify Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂, respectively, and the effects of coating layers with distinct crystalline states on the crystal structure, diffusion kinetics, and cell performance of host materials are further explored. A coating layer with high crystallinity enables mitigatory voltage decay and better cyclic stability of materials, while a coating layer with planar defects facilitates Li⁺ transfer and enhances the rate performance of materials. Consequently, optimizing the crystalline state of coating substances is critical for preferable surface modification.

Validating the Electronic Structure of Vanadium Phosphate Cathode Materials

Investigation of the electronic structure of contending battery electrode materials is an essential step for developing a detailed mechanistic understanding of charge-discharge properties. Herein, we use synchrotron soft X-ray absorption spectroscopy (XAS) in combination with complementary experiments and density functional theory calculations to map the electronic structure, band positioning, and band gap of prototype vanadium(III) phosphate cathode materials, Na₃V₂(PO₄)₃, Li₃V₂(PO₄)₃, and K₃V₃(PO₄)₄·H₂O, for alkali-ion rechargeable batteries. XAS fluorescence yield and electron yield measurements reveal substantial variation in surface-to-bulk atomic structure, vanadium oxidation states, and density of oxygen hole states across all samples. We attribute this variation to an intrinsic alkali metal surface depletion identified across these alkali metal vanadium(III) phosphates. We propose that an alkali-depleted surface provides a beneficial interface with the bulk structure(s) that raises the Fermi level and improves surface charge transfer kinetics. Furthermore, we discuss how this effect can play a significant role in reducing the electronic and ionic diffusion limitations of alkali vanadium phosphates in alkali-ion rechargeable batteries. These findings clarify the electronic structure and properties of alkali metal vanadium phosphates and offer guidance on future strategies to improve vanadium phosphate battery performance.

Improved electrochemical properties of LiNi0.91Co0.06Mn0.03O2 cathode material via Li-reactive coating with metal phosphates

Ni-rich layered oxides are promising cathode materials due to their high capacities. However, their synthesis process retains a large amount of Li residue on the surface, which is a main source of gas generation during operation of the battery. In this study, combined with simulation and experiment, we propose the optimal metal phosphate coating materials for removing residual Li from the surface of the Ni-rich layered oxide cathode material LiNi_0.91Co_0.06Mn_0.03O₂. First-principles-based screening process for 16 metal phosphates is performed to identify an ideal coating material that is highly reactive to Li₂O. By constructing the phase diagram, we obtain the equilibrium phases from the reaction of coating materials and Li₂O, based on a database using a DFT hybrid functional. Experimental verification for this approach is accomplished with Mn₃(PO₄)₂, Co₃(PO₄)₂, Fe₃(PO₄)₂, and TiPO₄. The Li-removing capabilities of these materials are comparable to the calculated results. In addition, electrochemical performances up to 50 charge/discharge cycles show that Mn-, Co-, Fe-phosphate materials are superior to an uncoated sample in terms of preventing capacity fading behavior, while TiPO₄ shows poor initial capacity and rapid reduction of capacity during cycling. Finally, Li-containing equilibrium phases examined from XRD analysis are in agreement with the simulation results.

Rapid Self-Assembly Spherical Li1.2Mn0.56Ni0.16Co0.08O2 with Improved Performances by Microwave Hydrothermal Method as Cathode for Lithium-Ion Batteries

Spherical Li-rich Li1.2Mn0.56Ni0.16Co0.08O2 compound is rapidly synthesized through a facile microwave hydrothermal method followed by a high-temperature solid-state reaction. Homogenous spherical precursor can be precipitated through the microwave hydrothermal (MH) method within 30 min without rigorous coprecipitation condition. The as-prepared Li-rich compound exhibits a hierarchical structure composed of spherical secondary particles (2-3 μm) and small primary particles (150-250 nm) with pores. X-ray diffractometry (XRD) and Brunauer-Emmett-Teller (BET) tests prove that a well-formed layered structure and a large specific surface area containing pores are obtained through the MH method. Such structure is a benefit for the thorough contact between active materials and electrolyte to increase the reactive points. Thus, the as-prepared Li-rich compound exhibits perfect electrochemical performances with a high discharge capacity of 235.6 mAh g(-1) at a current density of 200 mA g(-1). Even at higher current densities of 1000 and 2000 mA g(-1), discharge capacities of 168.6 and 131.2 mAh g(-1) are still maintained, respectively. Furthermore, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic intermittent titration technique (GITT) are carried out to study the material prepared by microwave hydrothermal method. It is considered as an efficient way to synthesize Li-rich compound as cathode material for applications.

Enhanced high rate performance of Li[Li0.17Ni0.2Co0.05Mn0.58−xAlx]O2−0.5x cathode material for lithium-ion batteries

Pristine LNCM and LNCMA as Li-rich cathode materials for lithium ion batteries were synthesized via a sol–gel route. The Al-substituted LNCM sample exhibits an enhanced high rate performance and superior cyclability.

Enhanced cycling performance of the Li4Ti5O12anode in an ethers electrolyte induced by a solid–electrolyte interphase film

Uniform solid–electrolyte interphase film can be generated on the surface of the Li₄Ti₅O₁₂anode in ethers electrolyte with lithium bis(trifluoromethanesulfonyl)imide as the lithium salt, leading to enhanced cycling stability and rate performance.