Zheng Si,Baozhao Shi,Jin Huang,Ye Yu,You Han,Jinli Zhang,Wei Li
Nickel-rich layered oxides (LiNixCoyMn1−x−yO2) (x ≥ 0.8, NCM) are intensively developed cathode materials for lithium-ion batteries owing to their high energy and low price, however, their application is impeded by poor cycle stability. Herein we explored a Ti and F co-doped Li(Ni0.8Co0.1Mn0.1)O2 cathode through a solid phase reaction using the precursors of TiO2 and NH4F. Combining the characterization results of XRD, Ar sputtering assisted XPS, HRTEM, in situ XRD, etc, it is illustrated that Ti4+ and F− co-modification can synergistically modulate the lattice parameter and the Ni2+/Li+ mixing degree for the Li(Ni0.8Co0.1Mn0.1)O2 cathode material. Particularly, density functional theory (DFT) calculations demonstrate that Ti and F co-doping is beneficial to form stable crystal structures with a layered phase and rock-salt phase. Ti4+ and F− co-dopants induce the formation of an ultra-thin rock-salt phase on the cathode surface, which provides a protective layer on the nickel-rich cathode surface, so as to enhance the electrochemical performance. The optimal Ti4+ and F− co-doped sample 0.5Ti@0.5F-NCM shows a superior discharge capacity of 202.2 mA h g−1 at 1C and 45 °C, and a capacity retention of 88.1% after 200 cycles, much higher than the retention of 45.2% for NCM. For 0.5Ti@0.5F-NCM, the lithium-ion diffusion coefficients after the 1st and 100th cycles are 2.67 × 10−11 cm2 s−1 and 7.14 × 10−12 cm2 s−1 respectively, larger than those of the pristine NCM (1.37 × 10−11 cm2 s−1 and 4.52 × 10−12 cm2 s−1). The Ti4+ and F− co-doping can suppress the H2–H3 phase change of the cathode during the charge and discharge process and reduce the charge transfer resistance. The results provide a simple and feasible design strategy via cation@anion dopants to boost the electrochemical performance of nickel-rich cathodes for lithium-ion batteries.
Jiahao Chen,Hong Zhang,Hongzhu Chen,Enjie Xia,Yanmei Wu,Zhicheng Li
Solid-state Li-ion batteries (LIBs) have recently attracted much attention for their high safety and energy density . Polyvinylidene fluoride (PVDF) is as a potential electrolyte for solid-state LIBs due to its high permittivity, wide voltage window and excellent thermal stability. Here, Y 3+ -doped Li 29 Zr 9 Nb 3 O 40 (LZNO) Li-ionic conductor with room temperature conductivity (σ 25 ) of 1.26 × 10 −4 S cm −1 is prepared. LZNO decorated PVDF-based composite solid electrolytes (CSEs) are fabricated. The PVDF-based CSE with 10% (mass ratio) of LZNO shows σ 25 of 2.34 × 10 −4 S cm −1 , and has thermal stability with melting temperature up to 332 °C and voltage window of 4.8 V. The assembled Li ( Ni 0.8 Co 0.1 Mn 0.1 ) O 2 |CSE|Li cells show initial specific discharge capacity of 216.7 mAh g −1 at 0.1 C, and exhibit high capacity and cycle performance. LiFePO 4 |CSE|Li cells display initial specific discharge capacity of 137.4 mAh g −1 at 0.5 C and high cycle performance. Addition of LZNO powder in CSEs can inhibit the dehydrofluorination of PVDF during the charge-discharge of cells, alleviate the deterioration of interface resistance, and greatly improve the specific discharge capacity of cells at high rates.
The development of high-performance solid-state batteries (SSBs) that integrate high safety with high energy density has long been pursued. However, conventional lithium-containing anode materials are unable to balance these two requirements, thereby necessitating the exploration of lithium-free anodes for SSBs. In the current study, a core–shell lithium-free α-Fe2O3@TiNb2O7 (TNO) nanofiber composite is synthesized and applied as an SSB anode. The confinement effect from the hollow TNO nanotubes on the encapsulated α-Fe2O3 nanoparticles can buffer the volume-change crushing during charging/discharging, leading to robust structural stability. Moreover, the high rate capability of TNO and high capacity of α-Fe2O3 work synergistically to provide superior electrochemical performances. The prepared α-Fe2O3@TNO composite delivers twice the reversible capacity (625 mA h g−1 at 0.1 A g−1) of pristine TNO as well as a remarkably prolonged cycle life (500 cycles with 79.2% capacity retention) and an improved rate performance (305 mA h g−1 at 3 A g−1) compared with those of α-Fe2O3, making this composite the most efficient TNO-based anode material ever reported. By pairing the composite with the high-energy Li[Ni0.8Co0.1Mn0.1]O2 (NCM811) cathode, the SSB full cell exhibits a high energy density of 400 W h kg−1. These results demonstrate the feasibility and great potential of the proposed lithium-free anode material in SSBs for practical applications.
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