Superior charge-transfer kinetics of NASICON-type Li3V2(PO4)3 cathodes by multivalent Al3+ and Cl− substitutions

Flexible All-Solid-State Li-Ion Battery Manufacturable in Ambient Atmosphere

The rational design and exploration of safe, robust, and inexpensive energy storage systems with high flexibility are greatly desired for integrated wearable electronic devices. Herein, a flexible all-solid-state battery possessing competitive electrochemical performance and mechanical stability has been realized by easy manufacture processes using carbon nanotube enhanced phosphate electrodes of LiTi₂(PO₄)₃ and Li₃V₂(PO₄)₃ and a highly conductive solid polymer electrolyte made of polyphosphazene/PVDF-HFP/LiBOB [PVDF-HFP, poly(vinylidene fluoride-co-hexafluoropropylene)]. The components were chosen based on their low toxicity, systematic manufacturability, and (electro-)chemical matching in order to ensure ambient atmosphere battery assembly and to reach high flexibility, good safety, effective interfacial contacts, and high chemical and mechanical stability for the battery while in operation. The high energy density of the electrodes was enabled by a novel design of the self-standing anode and cathode in a way that a large amount of active particles are embedded in the carbon nanotube (CNT) bunches and on the surface of CNT fabric, without binder additive, additional carbon, or a large metallic current collector. The electrodes showed outstanding performance individually in half-cells with liquid and polymer electrolyte, respectively. The prepared flexible all-solid-state battery exhibited good rate capability, and more than half of its theoretical capacity can be delivered even at 1C at 30 °C. Moreover, the capacity retentions are higher than 75% after 200 cycles at different current rates, and the battery showed smaller capacity fading after cycling at 50 °C. Furthermore, the promising practical possibilities of the battery concept and fabrication method were demonstrated by a prototype laminated flexible cell.

Effect of Reducing Agent on Solution Synthesis of Li3V2(PO4)3 Cathode Material for Lithium Ion Batteries

In this study, Li₃V₂(PO₄)₃ (LVP) powders are prepared by a solution synthesis method. The effects of two reducing agents on crystal structure and morphology and electrochemical properties are investigated. Preliminary studies on reducing agents such as oxalic acid and citric acid, are used to reduce the vanadium (V) precursor. The oxalic acid-assisted synthesis induces smaller particles (30 nm) compared with the citric acid-assisted synthesis (70 nm). The LVP powders obtained by the oxalic acid exhibit a higher specific capacity (124 mAh g⁻¹ at 1C) and better cycling performance (122 mAh g⁻¹ following 50 cycles at 1C rate) than those for the citric acid. This is due to their higher electronic conductivity caused by carbon coating and downsizing the particles. The charge-discharge plateaus obtained from cyclic voltammetry are in good agreement with galvanostatic cycling profiles.

Magnesium/chloride co-doping of lithium vanadium phosphate cathodes for enhanced stable lifetime in lithium-ion batteries

Combining XRD with ³¹P NMR, it is demonstrated that the Mg and Cl atoms of the new Mg and Cl co-doped Li₃V₂(PO₄)₃/C material occupy V and O sites in its structure, respectively.

Impact of Cl Doping on Electrochemical Performance in Orthosilicate (Li2FeSiO4): A Density Functional Theory Supported Experimental Approach

Safe and high-capacity cathode materials are a long quest for commercial lithium-ion battery development. Among various searched cathode materials, Li₂FeSiO₄ has taken the attention due to optimal working voltage, high elemental abundance, and low toxicity. However, as per our understanding and observation, the electrochemical performance of this material is significantly limited by the intrinsic low electronic conductivity and slow lithium-ion diffusion, which limits the practical capacity (a theoretical value of ∼330 mAh g^-1). In this report, using first-principles density functional theory based approach, we demonstrate that chlorine doping on oxygen site can enhance the electronic conductivity of the electrode and concurrently improve the electrochemical performance. Experimentally, X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission gun scanning electron microscopy elemental mapping confirms Cl doping in Li_2-xFeSiO_4-xCl_x/C (x ≤ 0.1), while electrochemical cycling performance demonstrated improved performance. The theoretical and experimental studies collectively predict that, via Cl doping, the lithium deinsertion voltage associated with the Fe²⁺/Fe³⁺ and Fe³⁺/Fe⁴⁺ redox couples can be reduced and electronic conductivity can be enhanced, which opens up the possibility of utilization of silicate-based cathode with carbonate-based commercial electrolyte. In view of potential and electronic conductivity benefits, our results indicate that Cl doping can be a promising low-cost method to improve the electrochemical performance of silicate-based cathode materials.

Rational Design and Facial Synthesis of Li3V2(PO4)3@C Nanocomposites Using Carbon with Different Dimensions for Ultrahigh-Rate Lithium-Ion Batteries

Li3V2(PO4)3 (LVP) particles dispersed in different inorganic carbons (LVP@C) have been successfully synthesized via an in situ synthesis method. The inorganic carbon materials with different dimensions including zero-dimensional Super P (SP) nanospheres, one-dimensional carbon nanotubes (CNTs), two-dimensional graphene nanosheets, and three-dimensional graphite particles. The effects of carbon dimensions on the structure, morphology, and electrochemical performance of LVP@C composites have been systematically investigated. The carbon materials can maintain their original morphology even after oxidation (by NH4VO3) and high-temperature sintering (850 °C). LVP@CNT exhibits the best electrochemical performances among all of the samples. At an ultrahigh discharge rate of 100C, it presents a discharge capacity of 91.94 mAh g(-1) (69.13% of its theoretical capacity) and maintains 79.82% of its original capacity even after 382 cycles. Its excellent electrochemical performance makes LVP@CNT a promising cathode candidate for lithium-ion batteries.

Effects of morphology on the electrochemical performances of Li3V2(PO4)3 cathode material for lithium ion batteries

The effects of various morphologies on the electrochemical performances of Li₃V₂(PO₄)₃ (LVP) were summarized and discussed.

Enhancement of the cycling performance of Li3V2(PO4)3/C by stabilizing the crystal structure through Zn2+ doping

Zn doping was proven to be helpful in stabilizing the crystal structure of Li₃V₂(PO₄)₃/C upon repeated cycles.