CN108428956B

CN108428956B - Cell capacity grading method of lithium ion battery

Info

Publication number: CN108428956B
Application number: CN201810070977.9A
Authority: CN
Inventors: 韩承宋; 尚随军; 郑荣鹏
Original assignee: Suzhou Youlion Battery Inc
Current assignee: Suzhou Youlion Battery Inc
Priority date: 2018-01-25
Filing date: 2018-01-25
Publication date: 2020-09-01
Anticipated expiration: 2038-01-25
Also published as: CN108428956A

Abstract

The invention provides a cell capacity grading method of a lithium ion battery, which comprises the following steps: 1) fully charging the battery cell; 2) finding a position with the maximum curve slope on an open-circuit voltage curve corresponding to the SOC of the battery cell; 3) obtaining a discharge current and a discharge time through the position; 4) discharging the battery cell according to the discharge current and the discharge time; 5) and measuring the voltage of the battery core. Compared with the prior art, the capacity grading discharge method has the advantages that the capacity grading discharge process is shortened, the capacity grading method is simple, about 40% of capacity grading electric energy can be saved, the capacity grading process time is greatly shortened, and the productivity can be effectively improved.

Description

Cell capacity grading method of lithium ion battery

Technical Field

The invention relates to a battery cell capacity grading method, in particular to a battery cell capacity grading method of a lithium ion battery.

Background

In the current production process of the lithium ion battery, the capacity grading of the battery core is usually required, the capacity grading of the battery core is actually a process of screening the actual capacity of the battery, and the actual capacity of the battery can be measured only in a discharging process unlike charging. For example, the discharge time of 1C5(5 is subscript) A discharge performance required in GB/T18287-2000 is not less than 51 minutes, while the industry generally has a minimum requirement of 60 minutes.

The capacity grading of the battery core is usually realized through a capacity grading cabinet, and the quality of the lithium ion battery can be effectively distinguished through the capacity grading. In the current capacity grading technology, a capacity grading method of full charge → full discharge → shipment charge → voltage measurement after stabilization is commonly adopted to realize capacity grading. The existing capacity grading technology has the defects that the time required by the capacity grading flow is long, the production efficiency is influenced, the power consumption in the capacity grading process is high, and electric energy is wasted.

Disclosure of Invention

In view of this, the invention provides a method for grading a battery cell of a lithium ion battery, which can effectively shorten the grading flow time and reduce the grading energy consumption.

The invention provides a cell capacity grading method of a lithium ion battery, which comprises the following steps:

1) fully charging the battery cell;

2) finding a position with the maximum curve slope on an open-circuit voltage curve corresponding to the SOC of the battery cell;

3) obtaining a discharge current and a discharge time through the position;

4) discharging the battery cell according to the discharge current and the discharge time;

5) and measuring the voltage of the battery core.

Further, the above discharge time (t) is obtained by the following formula:

discharge time (t) is (1-SOC at position (a)/discharge current (I).

Further, the discharge current (I) is a discharge C rate at the position (a).

Compared with the prior art, the cell capacity grading method of the lithium ion battery provided by the invention has the following advantages: when capacity grading is carried out on the battery cell, after the battery cell is fully charged, the position with larger slope of the curve is found out according to the open-circuit voltage curve corresponding to the SOC of the battery cell, the battery cell is uniformly discharged for a certain time according to a certain current, and the capacity grading is carried out on the battery cell according to the stabilized voltage; therefore, the shipment charging process is omitted, the capacity grading discharging process is shortened, the capacity grading method is simple, about 40% of capacity grading electric energy can be saved, the capacity grading process time is greatly shortened, and the productivity can be effectively improved.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:

fig. 1 is a schematic diagram of an open-circuit voltage curve corresponding to a cell SOC in a cell capacity grading method for a lithium ion battery according to an embodiment of the present invention;

fig. 2 is a schematic diagram of a data fitting degree between a cell capacity and a normal capacity in the cell capacity grading method for a lithium ion battery according to the embodiment of the present invention.

Detailed Description

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

Referring to fig. 1, a cell capacity grading method of a lithium ion battery according to an embodiment of the present invention is shown, and includes the following steps:

1) fully charging the battery cell;

2) on an open circuit voltage curve corresponding to the SOC of the battery cell, a position A with the maximum curve slope is found to be near the SOC 30 percent and meets the delivery requirement, so the position A is selected as a capacity grading point,

3) obtaining a discharge current I of 0.5C through the position A (a proper C rate can be selected according to specific conditions, and the value of the C rate is within the C rate range of the design of the battery cell);

discharge time t ═ (1-selected SOC)/selected discharge C rate, i.e., t ═ 1-30%/0.5 ═ 1.4h ═ 84mi n;

thus the step of the partial volume discharge adopts a discharge current of 0.5C and a discharge time of 84 minutes;

4) discharging the battery cell according to the discharge current I and the discharge time t;

5) and measuring the voltage of the battery core.

Referring to fig. 2, after capacity grading is performed on the test battery cell according to the above process, normal capacity grading is performed, the fitting degree of data obtained twice is good, a voltage interval (3821-3834.8) is obtained, and specific grading can be performed according to specific conditions in the voltage interval.

The comparison of the capacity grading experimental data of the test cell provided in this embodiment and the cell in the prior art is as follows:

therefore, after the capacity grading method is adopted, the capacity grading energy consumption is reduced, and the capacity grading time is shortened.

In summary, the cell capacity grading method for the lithium ion battery provided by the embodiment of the invention has the following advantages compared with the prior art: when capacity grading is carried out on the battery cell, after the battery cell is fully charged, the position with larger slope of the curve is found out according to the open-circuit voltage curve corresponding to the SOC of the battery cell, the battery cell is uniformly discharged for a certain time according to a certain current, and the capacity grading is carried out on the battery cell according to the stabilized voltage; therefore, the shipment charging process is omitted, the capacity grading discharging process is shortened, the capacity grading method is simple, about 40% of capacity grading electric energy can be saved, the capacity grading process time is greatly shortened, and the productivity can be effectively improved.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims

1. A method for dividing the capacity of a battery core of a lithium ion battery is characterized by comprising the following steps:

1) fully charging the battery cell;

2) finding a position (A) with the maximum curve slope on an open-circuit voltage curve corresponding to the SOC of the battery cell;

3) obtaining a discharge current (I) and a discharge time (t) through said location (A);

4) discharging the cell according to the discharge current (I) and the discharge time (t);

5) measuring the voltage of the battery cell;

the discharge time (t) is obtained by the following formula:

discharge time (t) is (1-SOC at position (a)/discharge current (I);

the discharge current (I) is a discharge C rate of the location (A).