NiMH No.7 battery.Effect of graphite anode on fast charging performance of lithium-ion batteries

　　The article analyzes the mechanism of the influence of graphite anode materials on the fast charging performance of lithium-ion batteries, prepares a series of graphite anode materials with different coke raw materials, conducts particle size, polarization and XRD tests on them, and makes lithium-ion batteries for rate testing. Charging and rate cycle testing.

　　The article analyzes the mechanism of the influence of graphite anode materials on the fast charging performance of lithium-ion batteries, prepares a series of graphite anode materials with different coke raw materials, conducts particle size, polarization and XRD tests on them, and makes lithium-ion batteries for rate testing. Charging and rate cycle testing. The results show that graphite materials prepared from coke raw materials with better orientation have better fast charging performance. A high-energy-density fast-charging lithium-ion battery was made using the improved graphite anode, and the capacity retention rate reached more than 86% in a 6C/1 rate cycle test for 300 weeks.

　　introduction

　　Since its inception, lithium-ion batteries have been widely used in many fields. From the current point of view, lithium-ion batteries are not only widely used in electronic products such as mobile phones, digital cameras, tablets, etc., but have also made certain breakthroughs in the field of vehicle power supply; judging from the future market demand for lithium-ion batteries: fast charging type Lithium-ion batteries will become an important direction for lithium-ion batteries.

　　In order to improve the fast charging performance of graphite anode materials, this paper experimentally prepared a series of graphite anode materials made from different coke raw materials, and conducted particle size, polarization and XRD tests on them to make lithium-ion batteries for rate charging and rate charging. Loop test. And the test results were analyzed.

　　Analysis of the fast charging mechanism of lithium-ion batteries and the impact of graphite on fast charging of lithium batteries

　　Taking lithium cobalt oxide as the positive electrode and graphite as the negative electrode as an example, the reactions of the positive and negative electrodes when charging a lithium-ion battery are as follows:

　　Positive electrode reaction equation: LiCoO2→Li1-xCoO2+xLi+xe-

　　Negative electrode reaction equation: xLi+xe-+6C→LixC6

　　When a lithium-ion battery is being charged, part of the Li+ in lithium cobalt oxide breaks away from the crystal lattice and enters the electrolyte, and then migrates (embedded) into the crystal lattice of the negative active material carbon to generate a LixC compound.

　　During this process, lithium ions migrate and diffuse from the positive electrode to the negative electrode under the action of the electric field and concentration gradient, and undergo liquid phase diffusion in the solution, electrochemical reaction on the graphite surface, and solid phase diffusion in the graphite.

　　The solid-phase diffusion coefficient of lithium inside graphite is relatively small (usually only about 10-10cm2.s-1), which makes the solid-phase diffusion of lithium inside graphite easily become the control step of the entire electrode reaction. Therefore, improving graphite materials and increasing the solid-phase diffusion of lithium in graphite can effectively reduce the risk of battery polarization and lithium precipitation, and improve the fast charging performance of lithium-ion batteries.

　　Preparation of graphite

　　Preparation of artificial graphite from different coke raw materials: Select different coke raw materials a, b, and c respectively. After pulverization and sieving, perform high-temperature graphitization at 2800°C. The temperature rise rate is 15°C/min, constant temperature. Time: 5 hours. The high-temperature treated material is sieved through a 250-mesh screen to obtain artificial graphite A, B, and C. The physical and chemical indicators of different artificial graphite materials are shown in Table 1.

　　Withdraw power assembly

　　Take the CR2016 button battery shell, drop electrolyte into the positive shell, and then put in the negative electrode sheet, separator (drop electrolyte on the negative electrode sheet and separator respectively), processed lithium sheets, nickel foam, and stainless steel sheets , cover the negative electrode shell to seal the battery, and make a CR2016 button battery.

　　Full battery assembly

　　Mix lithium cobalt oxide, PVDF, conductive agent carbon black SuperP and solvent NMP with a mass ratio of 96.5:1.5:2, and then coat them on a 16 μm thick aluminum foil; mix artificial graphite with a mass ratio of 96:3:1, The binder (sodium carboxymethyl cellulose CMC, styrene-butadiene rubber SBR = 1:1) and the conductive agent carbon black SuperP were mixed with the solvent deionized water and then coated on a 10 μm thick copper foil. The coated positive and negative electrode sheets undergo processes such as sheeting, winding, drying, liquid injection, sealing, formation, and volume separation to make the 554065 soft-pack lithium-ion battery.

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