Gradient potential distribution composite electrode, preparation method thereof and power battery

Abstract

The invention relates to the technical field of power batteries, in particular to a gradient potential distribution composite electrode, a preparation method of the composite electrode and a power battery. The preparation method comprises the following steps that a multi-layer co-extrusion coating method is adopted, one side of a current collector is coated with multiple kinds of electrode active slurry at the same time, multiple electrode active layers are formed, and the potential gradient of the multiple electrode active layers is gradually increased or gradually decreased in the direction away from the current collector; by adopting the multi-layer coextrusion coating method, the other side of the current collector is coated with multiple electrode active slurry at the same time to form multiple electrode active layers, and the electrode active layers on the two sides are symmetrically distributed with the current collector as the axis, wherein the number of layers is not less than 2. According to the invention, various defects caused by preparation of multiple electrode active layers by a layer-by-layer coating method are solved, the interface performance of each potential electrode active layer in the composite electrode with gradient potential distribution can be improved, and the safety of the battery under the condition of internal short circuit thermal runaway is further improved.

Description

technical field [0001] The invention relates to the technical field of power batteries, in particular to a composite electrode with gradient potential distribution, a preparation method thereof and a power battery. Background technique [0002] The safety of power batteries is a common problem faced by the entire battery industry at present. The frequent fire accidents of new energy vehicles in recent years have raised the intrinsic safety of batteries to the height that determines the fate of the entire industry. The thermal runaway of lithium-ion batteries is the core cause of power battery safety accidents. How to improve the safety of power batteries from the cell level is imminent. [0003] The battery cell includes positive and negative electrodes. How to design and prepare positive and negative electrode materials to improve the safety of the battery in the case of internal short-circuit thermal runaway is a key research topic in the industry. [0004] In addition, w...

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Problems solved by technology

But in actual application, if it is to prepare the positive sheet that contains multi-layer positive electrode active layer, there are following problems: 1. Before coating the second active layer, if the first active layer is not subjected to rolling pretreatment, then coating When laying the second layer of material, the solvent in the second layer of slurry will quickly penetrate into the first active layer, slowly volatilize and penetrate the second active layer during the subsequent baking process, resulting in residues on the surface of the second active layer A large number of pore defects affect the consistency of the final battery; 2. Before coating the second active layer, if the first active layer is pretreated by rolling, the rolling process will be in the coating area and blank area of ​​​​the current collector. Uneven stress distribution occurs, which leads to serious curling and even belt breakage of the positive electrode sheet in the drying tunnel when coating the second active layer

If the third and fourth layers of coating are also carried out, the problem is even more serious; if it is to prepare a negative electrode sheet containing a multilayer negative electrode active layer, there are the following problems: one, the negative electrode slurry usually adopts water-based slurry, and the water-based slurry Poor adhesion, if the water-based slurry is still used for the second coating, the bottom coating layer will be peeled off from the current collector, resulting in coating failure; if the oil-based slurry is used for coating, it is still inevitable The defect of partial powder falling; 2. The whole process is coated with oily slurry successively, which increases the environmental protection requirements of equipment and environment, as well as the complexity of the process, increases the cost and increases the number of defects

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