Lithium battery diaphragm, the main role of the diaphragm is to make the positive and negative electrodes of the battery separated to prevent the two poles from contacting and short circuit, in addition to the function of enabling the passage of electrolyte ions. Diaphragm coated with aluminum oxide, when the current is too large, can block the current. It has very good thermal conductivity, and when the battery temperature is too high, this material can conduct heat well, thus solving the problem of poor thermal conductivity of PP/PE materials. And it can be coated on the positive and negative electrodes to prolong the service life.