Metal Powder On The Performance Of Lithium-ion Battery, The Conductive Agent

With the rapid development of electronic facilities as well as energy and environmental concerning, people make high demands on batteries. Lithium-ion batteries are widely used as a new clean and high energy source for their favorable advantages of high voltage, big specific capacity, long cycling life and non-pollution. In future, the lithium ion power batteries for electrical vehicles will be the developing direction of the transportation industry.Based on summarizing the status quo and development of Li-ion batteries and their correlative materials, we compared the advantages and shortcomings of four kinds of the most popular positive materials, analyzed the requirements of power batteries for electric vehicles. It is known that the deficiency in these cathode materials is lower conductance, so the aim of our investigations is to improve the larger charge-discharge performance with better conductive addictive in this paper.First, the surface treatment on the graphite and acetylene black was carried out as following. They are put into acetone and mixed for 10 minutes, then filtered and dried. The conductive addictive was mixed with LiMn₂O₄ and the PVDF solution mass ratio with 8:85:7, then making them into electrode and assembling to battery to test the electrochemical performance. Comparing the samples with surface treatment and without treatment, we can draw these conclusions: (1) the special capacity and circle performance can be improved with the cleaned conductive addictive in electrode under larger charge-discharge current. It can be attributed that graphite and the acetylene black was covered with a layer of lipid substance which arises resistance to the electron and the lithium ion transfer, but the acetone can remove this lipid substance well; (2) With the same mass contents, the battery which added graphite as the conductive additive has better cycling performance than that of acetylene black, but the acetylene black samples have highly special capacity. It is because that the particle size of acetylene black is smaller than that of graphite, it is easy to disperse well among active material. It can also result from that the conductance rate of acetylene black and the transfer rate of lithium ion are higher thanthat of graphite.Secondly, the adding metal powder in conductive additive has been investigated to increase conductance. The acetylene black was chosen as the conductance main body in this research, the certain amount of the metal powder was added to increase the electrode conductance and improve the performance of larger charge-discharge current. Results show as following: (1) no matter how many mass, the capacity of batteries is little when the addictive is copper powder, because there is a potential between copper powder and aluminum foil which disturbs the inside electric field and resists the moving of electron and lithium ion; (2) adding aluminum powder as the addictive agent can improve the battery capacities at larger current with small amount. On the contrary, the special capacity is lower with larger amount which can be ascribed that aluminum powder affects the transfer between electron and lithium ion. By the comparison, it can be found that the performance of battery is best when the adding content is between 0.5 0.75% (ωt%)in the conductive additive; (3)comparing several adding methods of aluminum powder, the cathode capacity is improved with manual mixture in the agate mortar before mixing materials, but the cycle behavior is not poor. It is because manual mixture can not obtain very homogeneous effect which affects the size of LiMn₂O₄ and the crystal structure. In addition, the nanometer aluminum powder is also very easy to oxidize to alumina, affecting the property of battery; (4) the mixed conductive additive was prepared by putting aluminum powder and acetylene black into agate ball-milling mixed for 8 hours with alcohol as dispersant, then dried in vacuum furnace and passed with 250 sieve sieving. The cycle behavior and capacity are improved at larger current. The capacity fading is only 4.6% at 0.2 mA with 15 cycles, 0.24% at 0.5 mA20 cycles and 8.7% at 0.8 mA 20 cycles. The special capacity is up to 97.5 mAh/g. It is found that adding aluminum powder can improve electrode conductivity and reduce the resistance by A.C. Impedance test.It is also discussed that the Ag powder was added into the electrode by utilizing the decomposition of AgNO₃, but the result is not so good. Scanning by SEM, the active material is broken with long time mixture or temperature is insufficient to decompose completely. The mixed conductive additive was put into the active material LiFePO₄ to improve the conductivity. The original sample with pure acetylene black has betterbehavior than the other sample at 0.2mA current, but the difference is larger when increase the charge-discharge current. The sample with 0.75% aluminum powder has the preferable performance, whose C_0.2/C_0.5 is the minimum. Maybe performance will be better after increasing aluminum contents.As a whole, the addition amount of aluminum powder in conductive addictive can improve the performance of lithium ion battery at larger current using LiMn₂O₄ as active material. But for the other material and metal conductive addictive, it need further investigation.