Discussion on Development Process and Technical Development Direction of Power Battery

According to the customer's demand decomposition, carry out step-by-step decomposition design, and each process will eventually be transformed into file input and output. The product design process is described in detail below.

GB / t34013-2017 specifications and dimensions of power batteries for electric vehicles

The most basic design includes that the negative electrode is 1-2mm wider than the positive electrode and the diaphragm is 2-4mm wider than the negative electrode. In order to ensure that the battery will not be short circuited due to misalignment, the lamination is equivalent to the parallel connection of multiple small pole pieces, and the winding is equivalent to a large pole piece

Due to the light weight of aluminum-plastic film and high utilization rate of internal space, soft pack battery is suitable for the development of battery with large energy density. However, the metal shell is limited by the internal space, and the general energy density is slightly lower than that of soft pack battery. Safety because the aluminum shell battery has the protection of metal shell, the safety will be higher, while the flexible packaging battery can only pass the safety test by relying on the performance of the material itself, which seems to be more difficult at present.

In terms of process difficulty, because the soft pack battery is a lot of small pole pieces, it has high requirements for die-cutting equipment, which is easy to produce large self discharge and local micro short circuit. At the same time, due to the limitation of internal space, there is less free electrolyte, and the cycle performance may be slightly poor.

The wound battery is relatively better and has some surplus, which is easy to realize automatic production. In terms of cost, because the wound battery has high requirements for shell welding, the cost is slightly higher, while the soft pack battery does not involve laser welding, focusing on packaging and low equipment investment.

According to the internal space of the battery, calculate the number of positive and negative poles of the cell and the layers of the diaphragm. According to the development of the industry, the relevant parameters of the material are carried out according to the previous test experience. The experimental verification needs to verify the compaction density, material performance, auxiliary material performance (including the verification of SBR, CMC, PVDF, conductive agent, etc.) based on the development of the platform model, The development of the final process also needs to be matched with the materials to obtain the final control plan and process flow chart. Now, in order to shorten the time, manufacturers combine experimental verification and process development, but the risk is often large. After all, the material system itself develops with the development of technology.

Each performance of each material has relevant detection standards. Some performance indexes of the positive and negative electrodes are directly related to the performance indexes of the battery. However, there is no suitable model for forward electrochemical performance simulation, which is only repaired according to the existing empirical data.

However, the increase of CO ratio leads to the decrease of cell parameters a and C and the increase of C / A, resulting in the decrease of capacity.

However, too high Mn content will reduce the gram capacity of the material, and it is easy to produce spinel phase and destroy the layered structure of the material.

However, too high Ni content will produce mixed discharge effect with Li , resulting in deterioration of cycle performance and rate performance, and too high pH value of high nickel materials will affect the actual use.

With the increase of nickel content, the capacity of the material is higher and higher, but the thermal stability of the material decreases gradually. Mn can stabilize the structure, while Ni does not have this function. With the increase of temperature,

The de lithium cathode material Ni migrates to the Li layer through the tetrahedral position, causing structural collapse and thermal stability problems.

The structure of the material changes from layered salt to spinel, and continues to change to rock salt structure. Each change has the release of oxygen, which accelerates the thermal runaway of the material.

For most material manufacturers, they do not produce precursors. There are special manufacturers of precursors. Raw material manufacturers purchase precursors from precursor manufacturers, and then sinter materials according to requirements. Materials with different properties are obtained according to different control conditions.

The serious gas production during NCA charging and discharging leads to the bulging and deformation of the battery, the decline of cycle and shelf life, and brings potential safety hazards to the battery. Therefore, NCA cathode material is usually used to make 18650 cylindrical battery,

To alleviate the bulging deformation of the battery. Tesla Model s adopts a high-capacity 3.1ahnca lithium battery pack jointly developed with Panasonic, which is composed of 7000 18650 cylindrical batteries.

Due to the harsh preparation conditions and relatively troublesome use of NCA, China prefers the ncm811 route and Japan and South Korea prefer the NCA route.

The performance of single crystal ncm523 material of a material manufacturer under different voltages. Although the increase of voltage is conducive to the improvement of energy density, it brings some difficulty to the matching of the whole system.

1. Oxide coating can improve the conductivity without affecting the process of lithium ion stripping, or provide a path, or protect the surface.

Low valence elements: Mg, Sr, Zn, Al, B, La

Tetravalent elements: Zr, Ti, Si, CE

High priced elements: V, W, Mo, Cr, etc

2. Electronic and fast ionic conductor

Electronics: C, graphene, azo, ITO, PPy, etc

Fast ions: LBO, LZO, NTP, li3po4, etc

3. Salt coating

AlF3, AlPO4, lialf4, etc

According to the recommendations of the expert group and the current technical level, improve the nickel content and the upper limit voltage of the material, assist other material technologies to upgrade the technology of the material, transition the negative electrode from graphite to silicon carbon, and finally realize the application of lithium metal negative electrode.

Editing: JQ

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