# US 10,770,746 B2 · Method for producing a lithium ion secondary battery

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- Number: US 10,770,746 B2
- Document ID: US10770746B2
- Status: Granted
- Kind: B2
- Application number: 15/544,623
- Filed: 2015-03-19
- Published: 2018-02-08
- Granted: 2020-09-08
- Earliest claimed: 2015-03-19
- Assignees: Envision AESC Japan Ltd.
- Applicants: Envision AESC Japan Ltd.
- Inventors: Ikuma Matsuzaki; Kazuki Miyatake; Keisuke Matsumoto; Kodai Nagano
- Web page: https://patentgrep.com/patent/US10770746B2

## CPC

- H01M 10/052: Li-accumulators
- H01M 10/058: Construction or manufacture
- H01M 50/443: Particulate material
- H01M 50/451: comprising layers of only organic material and layers containing inorganic material
- Y02E 60/10: Energy storage using batteries
- Y02P 70/50: Manufacturing or production processes characterised by the final manufactured product
- H01M: PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

A method for producing a lithium ion secondary battery in which a positive electrode, a heat-resistant insulating layer provided separator having a heat-resistant insulating layer formed of oxide particles on one surface of a resin porous substrate, and a negative electrode are laminated on one another, and a nonaqueous electrolyte is impregnated in the heat-resistant insulating layer provided separator, includes drying the heat-resistant insulating layer provided separator before laminating so that the water content in the heat-resistant insulating layer provided separator remains in a predetermined range. In the drying, the water content in the heat-resistant insulating layer provided separator is decreased to the predetermined range by controlling the dew point and maintaining the predetermined range after reaching the predetermined range of water content.

## Claims

### Claim 1

A method for producing a lithium ion secondary battery in which a positive electrode, a heat-resistant insulating layer provided separator having a heat-resistant insulating layer formed of oxide particles on one surface of a resin porous substrate, and a negative electrode are laminated on one another, and a nonaqueous electrolyte is impregnated in the heat-resistant insulating layer provided separator, comprising:
drying the heat-resistant insulating layer provided separator before laminating so that a water content in the heat-resistant insulating layer provided separator remains in a predetermined range,
wherein, in the drying, the water content in the heat-resistant insulating layer provided separator is decreased to the predetermined range by controlling a dew point and maintaining the predetermined range after reaching the predetermined range of the water content, and
wherein, in the drying, the heat-resistant insulating layer provided separator is dried by setting the dew point so as to attain a water content decrease rate such that a shape of the heat-resistant insulating layer provided separator after the drying defined by a length ratio Y that is a ratio of a length of the resin porous substrate to a length of the heat-resistant insulating layer satisfies an equation:
1−4πX≤Y≤1+4πX,
wherein D represents a thickness of the separator, L represents a length of the separator, and X represents a ratio (D/L) of the thickness D to the length L of the separator,
wherein, in the drying, the water content is decreased such that a water decrease rate ((1−W)/T) satisfies an equation:
((1−W)/T)≤1.2, and
wherein W is a water content ratio W=w2/w1, T is a drying time of 0.5 hour, w1 is a water content before starting the drying, and w2 is a water content that is measured when T elapses after starting the drying.

### Claim 2 (depends on 1)

The method for producing a lithium ion secondary battery according to claim 1, wherein, in the drying step, the heat-resistant insulating layer provided separator is dried such that the water content to remain in the predetermined range is controlled to satisfy an equation:
0.4≤W<1.

### Claim 3 (depends on 1)

The method for producing a lithium ion secondary battery according to claim 1, wherein the lithium ion secondary battery comprises a ratio of a battery cell area to rated capacity is 5 cm2/Ah or more, and the rated capacity is at least 3 Ah or more.