This paper studies the various electrochemical properties of the soft-packaged lithium-ion battery and the differences between it and the stainless steel-cased lithium-ion battery to verify the possibility of industrialization of the soft-packaged lithium-ion battery.

　　Lithium-ion batteries are undoubtedly a new generation of batteries with a high technological content and a wide range of applications. It has high volume ratio energy and mass ratio energy, rechargeable and pollution-free, and possesses the three major advantages of the current battery industry development. It is called "the most promising chemical power source".

　　Stainless steel shell lithium ion battery, polymer lithium ion battery and soft package lithium ion battery three different technologies are compared as listed in Table 1. This paper studies the various electrochemical properties of the soft-packaged lithium-ion battery and the differences between it and the stainless steel-cased lithium-ion battery to verify the possibility of industrialization of the soft-packaged lithium-ion battery.

　　Research on the performance of soft-packaged lithium-ion battery

　　1, experiment

　　The positive electrode material used in the experimental battery is lithium cobalt oxide, and the negative electrode material is artificial spherical graphite. LiPF/EC/DEC/DMC is the electrolyte, in which LiPF is a conductive salt, and EC (ethylene carbonate)/DEC (diethyl carbonate)/DMC (dimethyl carbonate) is a composite solvent. The outer packaging of the battery is a composite aluminum plastic film, and its structure is five layers of PET (polyester) / glue / Al / glue / PP (polypropylene). The battery tab sealing glue is a modified polyolefin material.

　　The battery manufacturing process includes batching, mixing, coating, rolling, slitting, spot welding, winding, sealing, forming, degassing, and volume division. A lithium-ion battery with a stainless steel case was fabricated at the same time under similar process conditions. The size of the soft-packaged lithium-ion battery and the stainless steel-cased lithium-ion battery are both 48mm&TImes;30mm&TImes;4.1mm. The nominal capacity of the two batteries is 500mA·h.

　　In the experiment, the pre-charging method was used to form the protective film of the negative electrode material. A part of the gas will be generated during the formation of the protective film, and then the generated gas will be removed by vacuum. In this way, the problem of battery gas swelling caused by the formation method is eliminated.

　　2. Results and discussion

　　2.1 Rate discharge performance

　　The reason is as follows: the outermost layer of the battery after the inner winding of the soft-packaged lithium-ion battery is the positive pole piece, and the outermost layer of the battery after the inner-winding of the stainless steel shell battery is the negative electrode. The amount of cathode material coating is more, and the discharge capacity of lithium-ion batteries is determined by the anode, so the capacity of soft-packaged batteries is relatively higher than that of stainless steel batteries. The internal cells of the battery adopt different structures, which are related to the materials used in the outer casing. The soft packaging lithium-ion battery shell is made of aluminum-plastic packaging film with an Al foil isolation layer as the middle layer. If it is in contact with the inner winding cell with the outermost layer as the negative pole piece, it will be at a very low potential (about 0 when fully charged. 05mVVS.Li) may cause the dissolution of the Al foil isolation layer of the flexible packaging, causing the battery to fail. If the stainless steel shell battery uses an internally wound cell with the outermost positive pole piece, there is a problem of welding between the tabs (usually Al strips) on the positive pole piece and the stainless steel shell, so the outermost layer is usually the negative pole piece. The inner winding cell. From the structural point of view, the soft-packaged lithium-ion battery has a competitive advantage over the stainless steel-cased lithium-ion battery in terms of capacity.

　　2.2 High and low temperature performance

　　It can be seen from the figure that the discharge capacity of the soft-packaged lithium-ion battery at a high temperature of 45cc and a low temperature of -10°C has reached 102.8% and 87.8% of the battery capacity at a normal temperature of 25°C. The battery has good high and low temperature performance. The high and low temperature performance of the lithium-ion battery with stainless steel casing, its discharge capacity at a high temperature of 45 ℃ and a low temperature of -10 ℃ reach 103.2% and 93.4% of the battery capacity at a normal temperature of 25 ℃. It can be seen from the figure that the discharge capacity retention rate of the soft-packaged lithium-ion battery at low temperatures is close to the capacity retention rate of the stainless steel-cased lithium-ion battery at low temperatures.

　　2.3 Cycle stability

　　Figure 3 is a comparison diagram of the cycle performance of two lithium-ion batteries. Wherein is the number of cycles, c is the battery capacity, and the battery charge-discharge cycle system is 1CmA charging to 4.2V, and constant voltage charging at this voltage for 2h and then standing still 10rain, then 1CmA discharge to 3.0V. After 300 cycles of the battery, the discharge capacity of the soft-packaged lithium-ion battery was maintained at about 90.6% of the initial capacity, while the discharge capacity of the stainless steel-case lithium-ion battery was maintained at 91.3% of the initial capacity. It can be seen from the figure that the lithium-ion battery made with the aluminum-plastic composite film packaging shell instead of the conventional metal shell is good in terms of cycle stability. The structure and material of the aluminum-plastic composite film and the performance of the tab sealant can completely isolate the interaction between the battery interior and the external environment. The aluminum-plastic composite film can complete a good sealing function similar to that of a metal casing.

　　The testing of other properties of soft-packaged lithium-ion batteries, such as storage performance, self-discharge performance and various safety performances, has been completed. The product basically meets the test requirements of the national standard "General Specification for Lithium-ion Batteries for Cellular Phones GB/T18287-2000). Flexible packaging lithium-ion products are currently being tested by the market, and are mainly used in MP3, wireless earphones, car DVDs and other applications.

　　3. Conclusion

　　Research on the electrochemical performance of soft-packaged lithium-ion batteries, such as rate discharge capacity, high and low temperature discharge capacity, and battery cycle stability, shows that the soft-packaged lithium-ion batteries have very high application value. It is not only different from the general metal shell lithium ion battery, but also different from the polymer lithium ion battery. It is a new type of lithium ion battery. This kind of battery has the advantages of high weight ratio energy, good shape plasticity and simple production process. Mass production. There are currently two common lithium-ion battery technologies: liquid lithium-ion batteries with metal shells and polymer lithium-ion batteries. The shell of liquid lithium-ion battery is generally steel shell or aluminum shell, and its plasticity is not as good as polymer lithium-ion battery. However, the manufacturing process of polymer lithium-ion batteries is complicated, especially the low yield, which greatly restricts the industrialization of this battery.