Lift silicon negative What do you think of it? Large-capacity, high-volume expansion? As a new generation of negative electrode material of lithium ion battery, the capacity of silicon negative electrode is up to 4200mAh / g, which is more than 10 times that of graphite negative electrode material. It is the most promising negative electrode material for the next generation lithium ion battery.
In this dazzling halo, silicon cathode also has insurmountable shortcomings. This is mainly due to the serious volume expansion of silicon negative electrode during lithium intercalation. Under complete lithium insertion, the volumetric expansion of silicon negative electrode can reach 300% This can result in pulverization and loss of the material particles, seriously affecting their electrochemical properties. Efforts to reduce the volume expansion of silicon anode materials, such as nano-particles, thin-film electrodes, carbon coating and other methods, are people to overcome the expansion of silicon negative efforts. Volume expansion is a bad news for Li-ion batteries, but let's take a closer look at the huge volumetric expansion of silicon negatives. Is there any other special envoy's use?
Jialiang Lang, Tsinghua University, who developed a "mini crane" that exploits the volume expansion of silicon negative electrodes during charge and discharge. The "mini crane" is actually a soft-pack lithium-ion battery with a LiFePO4 material with a small change of volume on the positive electrode and a silicon negative electrode material on the negative electrode with a capacity of 2.1 Ah. And the use of the battery was "water test" in the experiment by charging the battery "lift" 637.5g of water in the fully charged state battery expansion pressure reached 25.8KPa, in the subsequent cycle In the average pressure of 21KPa. Subsequent studies show that the battery can produce the highest pressure up to 17MPa. During the entire charge and discharge voltage platform, the battery can continue to produce more than 10MPa pressure. In the process, the energy generated by charging is divided into three parts, part of which is converted into mechanical energy, part of which is converted to chemical energy stored in the battery, and part of the energy is dissipated as heat energy.
Of course, the ability to respond quickly to a device intended to convert electrical energy to mechanical energy is of course very important, and Jialiang Lang studied the battery's response to volumetric expansion in fast charge-discharge mode. Studies have shown that battery expansion has a good response to pulsed current. And the expansion distance and charging time showed a linear relationship, the current density of 2A / g, the expansion rate of 1.6nm / s, so the program can be used for the positioning of nano-precision. The expansion rate of the battery is mainly related to the surface density of the negative electrode of the silicon, the thickness of the battery and the current density. Therefore, under the premise of battery shaping, we can control the expansion rate of the battery by controlling the current so as to achieve the control precision we need. In this study, the capacity of the Si negative electrode exerted only 800 mAh / g, so the "mini crane" still has a lot of room for improvement. The "mini-jack" accurately produces nanoscale displacements and is capable of withstanding tremendous loads, enabling it to be used in applications requiring high-precision positioning on the nanometer scale, such as probes that operate a scanning tunneling microscope. In the opposite direction, often can achieve good results.
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