It is reported that the Chinese Academy of Sciences, Shenyang Institute of Materials Science (Joint) Laboratory of High Performance Ceramic Materials Research Group Wang Xiaohui research group based on previous studies, through the creation of extreme water shortage of the acidic synthesis environment, the first time in the world to prepare a 12 nm thick [100] oriented LiFePO4 thin nanosheets. This work provides a new method and perspective for further improving the rate performance of lithium-ion batteries in the future.
Lithium-ion battery is the necessary power source of mobile electronic devices in today's society. It consists of positive electrode, negative electrode, separator, electrolyte and so on. Its key performance indicators (such as rate capability and cycle life) are determined by the electrochemical performance 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 Chinese Academy of Sciences Institute of Metal Shenyang National Laboratory of Materials Science (high performance ceramic materials Wang Xiaohui research group based on previous studies (J.Phys.Chem.C114: 16806 (2010); Phys.Chem. CrystEngCommun 16: 10112 (2014)), for the first time in the world, [100] oriented LiFePO4 ultrathin nanosheets have been prepared for the first time in the world by creating an extremely acidic environment that is dehydrated. 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 10C (60 minutes / 10 = 6 minutes) charge and discharge rate, after 1000 cycles to maintain the initial capacity of 90%. At 20C 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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