Lithium iron phosphate (LiFePO 4 ) is one of the most important cathode materials for high-performance lithium-ion batteries in the future due to its high safety, high reversibility, and good repeatability. However, high cost of lithium salt makes it difficult to large scale production in hydrothermal method . Therefore, it is urgent to reduce production costs of LiFePO 4 while maintaining the unique advantages of hydrothermal methods. In this work, the lithium iron phosphate powders (LFP-twi) with low Fe-Li anti-site defect concentration and inhibition along the direction [010] was constructed by hydrothermal reaction with low lithium usage. As a result, this allows the material to have an excellent reversible capacity (163.6 mAhg −1 at 0.1 C), ultra-high-rate capability (120 mAhg −1 at 10 C), and noticeable low-temperature performance (130 mAhg −1 at - 20 ℃ and 0.1 C). These findings open a new avenue for the development of high-density current and low-temperature resistant LiFePO 4 batteries.
Nickel-rich layered LiNi x Co y Mn 1- x - y O 2 (NCM, x ≥ 0.83) is considered as a promising cathode material for lithium-ion batteries (LIBs), owing to its satisfying specific energy. However, the undesired phase transformation from layered into rock-salt at the NCM surface will easily induce Li concentration gradient during cycling, which hinders the Li-ions diffusion and leads to the gradual accumulation of inner stress with the appearance of microcracks. Herein, we propose a surficial engineering strategy to promote the Li-ions transmission for single-crystalline LiNi 0.83 Co 0.11 Mn 0.06 O 2 (SCNCM) via Li 1.3 In 0.3 Ti 1.7 (PO 4 ) 3 (LITP) modification. It is noted that, as the fast Li-ion conductor, LITP can accelerate the Li-ions diffusion and alleviate the electrode–electrolyte side reaction simultaneously. More importantly, LITP can serve as the Li-ions regulator, ensuring the homogeneous distribution of Li-ions and minimizing the concentration difference at SCNCM surface. It can relieve the stress induced by the inconsistent Li-ions dispersion, which effectively decreases the degree of structural disordering and lattice mismatch at surface, eventually maintaining the high structure integrity during long-term cycling. As anticipated, even under the harsh testing conditions, the LITP modified SCNCM still can achieve a satisfied reversible capacity of 196.4 mAh g −1 under potential range of 2.75–4.6 V after 200 cycles at 25 °C in coin-type half-cells. Furthermore, it provides an extraordinary capacity retention of 88% in 2.75–4.3 V after 400 cycles at high temperature of 45 °C in pouch-type full-battery.
The Li + concentration and Li + transport channel size of garnet-type solid electrolyte Li 7 La 3 Zr 2 O 12 are the two key factors associated with the improvement of Li ionic conductivity . Through precise control of the Li + concentration and the Li + transport channel size by Ta-doping (Li 7-X La 3 Zr 2-X Ta X O 12 , X = 0.2–1.0), synergistic regulation of the two factors is achieved. Results show that the optimum Li + concentration seems to be at about 6.31 where the Li + occupancy in LiO 6 is high and the Li + arrangement in LiO 4 is disordering. With the Li + concentration higher than 6.31, the occupancy in LiO 4 sites remains constant but the Li + arrangement in LiO 4 becomes more and more ordering. At higher Li + concentration of 6.52, Li + arrangement becomes certain of ordering which should have reduced the grain conductivity, however, the grain conductivity is still as high as 9.84 × 10 −4 S cm −1 . This indicates that LLZO with this Li + concentration have favorable Li + transport channel size. The optimum Li + transport channel size is about 12.95 ± 0.01 Å. At Li + concentration of 6.31, the proper Li + concentration is the main factor for the high grain ionic conductivity of 10.1 × 10 −4 S cm −1 . While at Li + concentration of 6.52, the suitable Li + transport channel size is the main factor for the high grain ionic conductivity. In conclusion, the high grain ionic conductivity at Li + concentration of 6.31–6.52 is due to the synergistic regulation of Li + concentration and Li + transport channel size.
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