Lithium batteries are the necessary power source for mobile electronic devices in today's society. They consist of positive electrodes, negative electrodes, separators, electrolytes, etc. The key performance indicators (such as magnification and cycle life) are determined by the electrochemical properties of the positive electrode material. LiFePO4 is a recognized cathode material. In order to improve its electrochemical performance, people have long been committed to reducing the diffusion distance of lithium ions, that is, decreasing the size of the [010] direction. Recent studies have shown that the electrode consists of a large number of particles, and its electrochemical performance depends mainly on the proportion of particles (activated particles) in the total number of particles involved in the electrochemical reaction during charging and discharging. Therefore, how to obtain LiFePO4 with a high ratio of activated particles is a key issue in the research of cathode materials.
In response to this problem, the Wang Xiaohui research group of the Research Department of High Performance Ceramics, Shenyang Institute of Materials Science, Shenyang Institute of Materials Science, China, based on the previous research (J. Phys. Chem. C 114: 16806 (2010) (100) -oriented LiFePO4 ultrathin nanosheets [12] have been produced for the first time in the world by creating an acidic synthesis environment that is extremely water-deficient. Chem. Phys. 14: 2669 (2012); CrystEngCommun 16: 10112 (2014) . The voltage hysteresis experiment results show that the electrode composed of this material has the smallest voltage gap so far, and the potentiostatic gap titration test results show that the electrode has high activation rate and conversion rate. These results indicate that the [100] orientation Electrodes made of LiFePO4 thin nanosheets have a high ratio of activated particles. Thus, the electrode has excellent rate performance and cycle life. At 10 C (60 minutes / 10 = 6 minutes) charge and discharge rate, after 1000 cycles to maintain the initial capacity of 90%. At 20 C charge and discharge rate, the capacity can still reach 72% of the theoretical capacity. This work provides a new method and perspective for further increasing the rate performance of lithium-ion batteries. In this way, the diffusion distance of lithium ions can be shortened not only by reducing the size of the [010] direction, but also by controlling the size of the [100] direction Improve the proportion of activated lithium-ion battery particles to improve lithium-ion battery rate performance. Relevant results are published in the January 13 issue of Nano Letters (16: 795-799) magazine.
This work is supported by the project of "Introduction of Outstanding Scholars" by the Metals Institute and the Youth Innovation Promotion Association of Chinese Academy of Sciences.
Figure 1 (a) newly synthesized sample and the sample is dispersed and then dropped onto amorphous silicon XRD patterns. (b) Schematic of Figure a. (c, d) TEM image of LiFePO4. (e) corresponds to the electron diffraction pattern of (d). Gaussian function fitting LiFePO4 grain size statistics in different directions. (f) a axis, 12 nm, (g) b axis, 134 nm, (h) c axis, 280 nm.
Figure 2 (a) [100] orientation, microwave assisted synthesis and [010] oriented LiFePO4 morphology diagram. (b) The voltage gap of three kinds of electrodes consisting of [100] orientation, microwave assisted synthesis, [010] oriented LiFePO4 at C / 2 to C / 100 at different charge and discharge currents. (c) The Li chemical potential in LiFePO4 as a function of Li fraction change, where there is a maximum transition barrier (Δμb) defined as the difference between the maximum and the chemical potential in the middle of the immiscible region. (d) Potentiostatic gap titration with [100] orientation and microwave-assisted synthesis of LiFePO4 electrode and its fitting experimental data.
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