Separator for lithium ion battery and preparation method of separator

Abstract

The invention discloses a separator for a lithium ion battery and belongs to the technical field of lithium ion batteries. The separator comprises a polymer microporous film substrate, wherein the surface of the substrate and the internal wall of a micropore duct of the substrate are coated with nano-oxide layers. The preparation method comprises the following steps: (1) performing oxidation treatment on the polymer microporous film with an acid solution, then washing the film successively with an alkali solution and deionized water and drying the film; (2) putting the film on an atomic layer deposition apparatus or a continuous atomic layer deposition device, then vacuumizing, heating to 50-100 DEG C and keeping for 1-30min; (3) introducing trimethylaluminum as a first precursor; (4) adding nitrogen or inert gas for purging; (5) introducing a second precursor; (6) adding nitrogen or inert gas for purging; (7) repeating steps (3)-(6); and (8) performing heat setting treatment. The separator disclosed by the invention is small in thickness and heat shrinkage, and is good in wetting property with electrolyte. The preparation process temperature is low, a formed coating is dense, and the thickness of the coating can be precisely controlled.

Description

technical field [0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a separator for lithium ion batteries and a preparation method thereof. Background technique [0002] At present, in the field of batteries, polyolefin microporous membranes are usually used as separators for blocking positive and negative electrodes. For example, lithium-ion battery separators commonly include polypropylene (PP) microporous membranes and polyethylene (PE) microporous membranes. However, due to the inherent characteristics of polyolefin polymers, its performance in batteries is affected, and even its application in some fields is hindered. [0003] The main disadvantages of polyolefin battery separators are: (1) Low surface energy and poor hydrophilicity; resulting in poor wettability between polyolefin separators and highly polar electrolytes, and poor liquid retention capacity, thus affecting battery performance. (2) Poor therm...

AI Technical Summary

Problems solved by technology

However, due to the inherent characteristics of polyolefin polymers, it affects its performance in batteries, and even hinders its application in some fields.

[0003] The disadvantages of polyolefin battery separators are mainly manifested in: (1) low surface energy and poor hydrophilicity; resulting in poor wettability between polyolefin separators and highly polar electrolytes, and poor liquid retention capacity, thus affecting battery performance

(2) Poor thermal stability, prone to thermal shrinkage; the battery will emit a lot of heat when charging and discharging with high current, and the battery temperature will remain at a relatively high level

However, the low thermal stability of the polyolefin separator leads to a large thermal shrinkage at high temperature, which increases the risk of short circuit in the battery.

(3) Insufficient electrochemical stability; although the polyolefin separator has good stability, it still cannot fully meet the requirements of the battery under the trend of high voltage and high capacity of the battery, and yellowing and mechanical properties will appear after long-term use. Reduced energy phenomenon, which in turn affects the service life of the battery

But the disadvantage is that the thickness of the diaphragm is increased more, which runs counter to the current direction of high capacity and miniaturization of batteries.

Moreover, the coating layer only exists on the outer surface of the diaphragm, and does not improve the inner wall of the microporous structure.

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