CN110165319B

CN110165319B - Sorting method for self-discharge performance of high-capacity lithium battery

Info

Publication number: CN110165319B
Application number: CN201910496955.3A
Authority: CN
Inventors: 曹长城; 曹成群; 张晓伟; 唐正果; 王改香
Original assignee: Henan Fusen New Energy Technology Co ltd
Current assignee: Henan Fusen New Energy Technology Co ltd
Priority date: 2019-06-10
Filing date: 2019-06-10
Publication date: 2022-02-22
Anticipated expiration: 2039-06-10
Also published as: CN110165319A

Abstract

The invention provides a sorting method for self-discharge performance of a high-capacity lithium battery, belonging to the technical field of lithium ion batteries and comprising the following steps: taking a lithium battery which is aged at the high temperature of 45 ℃ for 2 days after liquid injection, and charging for 90 minutes by adopting a constant current of 0.05-0.1C; charging for 90 minutes by adopting a constant current of 0.1-0.2C; the high-voltage power supply is formed by constant current and constant voltage of 0.3C, the upper limit protection voltage is 4.3V, and the cut-off current is 0.01C; then testing OCV1 by using a tester with the voltage precision of 0.0001V, standing at the high temperature of 40-45 ℃ for 3 days, standing at the normal temperature for 12 hours, and testing OCV 2; screening batteries with large self-discharge difference by settling the difference value between the OCV1 and the OCV 2; according to the conventional 0.5C charge-discharge detection capacity of the lithium battery, testing the OCV3 in a cabinet after 0.5C constant-current charging for 60 minutes and pressure limitation for 4.2V, testing the OCV4 after standing for 7 days at normal temperature, and controlling the battery to be qualified within less than or equal to 9mv through settling the difference value between the OCV3 and the OCV 4. The lithium battery manufactured by the invention can reduce the number of secondary capacity-divided batteries and simultaneously improve the consistency and safety of grouping use of subsequent lithium batteries.

Description

Sorting method for self-discharge performance of high-capacity lithium battery

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a high-capacity lithium battery self-discharge performance sorting method with high economic usability and safety.

Background

Currently, lithium ion batteries are in the leading position with absolute advantages in the 3C (computer, communication, consumer electronics) field compared to nickel-hydrogen and nickel-cadmium batteries; meanwhile, in order to meet the requirements of energy conservation and environmental protection, electric vehicles (including electric bicycles and electric automobiles) have wide market prospects. As a power source of an electric vehicle, a lithium ion battery has a very large competitive power. In the field of 3C electronics consumption or in the field of electric vehicle applications, batteries must be connected in parallel and in series in a certain manner due to the high demand for energy from the power supply. Such use of batteries in groups requires that the cells must have good consistency. However, due to the limitations of current battery manufacturing processes and equipment and the differences in raw material incoming material properties, the consistency of lithium ion batteries (especially high capacity batteries) is to be improved; due to the requirement of energy density, the adopted materials and process design of the high-capacity lithium battery are relatively close to the limit value, and the electrolyte is difficult to fully permeate in the later period; considering that the economical efficiency and production efficiency of practical application generally adopt a mode of gradually increasing multi-stage constant-current time-limited charging or one-time constant-voltage charging 4.2V constant-current constant-voltage formation, internal active substances can not be fully activated, and the cells with high probability self-discharge can not be effectively sorted; in addition, when the batteries are used in groups, the market general IC upper limit protection voltage of the protection plate is 4.25 +/-0.05V, the detection upper limit voltage in the actual production process of the lithium battery industry is 4.2V, the side reaction of partial active substances in the lithium battery is insufficient due to the difference between application and detection, and partial poor batteries with large self-discharge cannot be screened out in time. Therefore, even if production enterprises strictly sort the lithium batteries, the discharge time of the whole lithium battery pack is short due to the fact that the voltages of the individual lithium batteries are inconsistent after the lithium batteries are actually grouped and used for multiple times; meanwhile, due to inconsistent voltage, single string is over-charged and over-discharged, and serious potential safety hazard exists.

In view of the above, there is a need for a self-discharge sorting method for high-capacity lithium batteries with high economical efficiency and safety.

Patent document CN106772109A discloses a method for sorting self-discharge performance of batteries. The sorting method comprises the following steps: discharging the batteries after capacity grading to cut-off voltage, then starting standing, and measuring the stable voltage V0 after standing for a first time; charging the battery to a set state, then starting to stand, and measuring an intermediate voltage V1 after standing for a second time; continuing to stand the battery under the environment of the set temperature, and measuring the final voltage V2 after standing for a third time; and calculating the self-discharge rate delta of the battery as (V1-V2)/(V1-V0), judging the grade of the battery according to the self-discharge rate delta and a standard value, and charging a small capacity into the battery to enable the voltage and the capacity of the battery to be in a certain proportional relation within a certain capacity threshold value, so that the high-efficiency self-discharge test can be realized through simple logistics line change.

Patent No. CN102303023B discloses a method for detecting and sorting self-discharge performance of lithium iron phosphate batteries. The method comprises the following steps: 1. charge to <70% SOC/; 2. storing for a period of time, which is called the settling time; 3. testing the open-circuit voltage of the battery, wherein the voltage measured in the step is called as V1; 4. storing for a period of time, which is called self-discharge time; 5. testing the open-circuit voltage of the battery, wherein the voltage measured in the step is called as V2; 6. calculating the voltage drop of the battery, wherein the voltage drop is called as delta V, and the delta V = V1-V2; 7. the battery with the delta V larger than the standard value is judged as a defective product, and the battery with the delta V smaller than or equal to the standard value is judged as a good product.

The method can select the self-discharge performance of the lithium iron phosphate battery in a short time without high-temperature aging, and solves the problem of high detection cost caused by the fact that the detection time is shortened by adopting a method of accelerating the discharge speed by high-temperature aging in the existing selection method.

The sorting method can sort out the self-discharge performance of the lithium battery within a certain time, but the defect that partial bad batteries with large self-discharge cannot be screened out in time exists, so that the voltage consistency of the lithium battery is poor.

Disclosure of Invention

The invention aims to solve the technical problem that aiming at the defects of the prior art, the invention provides a method for realizing potential self-discharge performance sorting by using a low-current 4.3V high-voltage formation method of a high-capacity lithium battery and according to the double standards of the voltage difference of two times of testing OCV1 and OCV2 and the voltage difference of two times of testing OCV3 and OCV4 after capacity grading, and the method has higher economic usability and safety.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

a sorting method for self-discharge performance of a high-capacity lithium battery comprises the following steps:

(1) taking a high-capacity lithium battery which is aged at the high temperature of 45 ℃ for 2 days after liquid injection;

(2) and (2) forming the lithium battery in the step (1) by the following steps: the first step is as follows: constant current charging is carried out at 0.05-0.1 ℃; the second step is that: charging by adopting a 0.1C constant current; the third step: the upper limit protection voltage is 4.3V and the cutoff current is 0.01C by adopting a 0.3C constant current and constant voltage;

(3) testing the lithium battery in the step (2) to obtain OCV1 by adopting a tester with the voltage precision of 0.0001V, standing at the high temperature of 40-45 ℃ for 3 days, and standing at the normal temperature for 12 hours to obtain OCV 2; screening batteries with large self-discharge difference by settling the difference value between the OCV1 and the OCV 2;

(4) grading the capacity of the lithium battery in the step (3) by adopting the following steps: 0.5C constant current discharge is carried out for 2.75V; charging at 0.5C with constant current and constant voltage for 4.2V, and cutting off current for 0.01C; ③ 0.5C constant current discharge 2.75V; fourthly, charging for 60 minutes at constant current of 0.5C, and limiting the voltage to 4.2V;

(5) testing the lithium battery in the step (4) into OCV3 by adopting a voltage internal resistance tester with the precision of 0.0001V, and testing OCV4 after the lithium battery is placed for 7 days at normal temperature; and the qualified battery is obtained when the settlement difference value is less than or equal to 9mv through settlement OCV3-OCV 4.

Further, in the step (2), the constant current charging time in the first step and the second step is 90 minutes.

Further, in the step (2), the current is cut off by 0.01C in the third step.

Further, in the step (4), the constant current charging is carried out for 60 minutes at 0.5C, and the voltage is limited to 4.2V.

Compared with the prior art, the invention has the following beneficial effects:

the lithium nickel cobalt manganese oxide material has mature technology, excellent cycle performance and high cost performance, and is preferred as a high-capacity lithium battery; however, because the nickel-cobalt lithium manganate has a large proportion of nickel components along with the increase of the capacity, the contents of residual carbonate, hydroxyl and the like on the surface are relatively high in the sintering process, and the pH value is relatively difficult to control compared with that of lithium cobaltate, lithium manganate and lithium iron phosphate. In the industrialized use process, the moisture content of the battery is easy to exceed the standard due to uncontrollable process environment, and the internal side reactant is higher than that of similar products. Meanwhile, the material compaction of the high-capacity battery process design material is close to the limit value of the material, and the conventional detection mode has certain defects on the separation of potential bad batteries; in consideration of various factors, the invention adopts a low-current and high-voltage mode to carry out formation, fully activates the generation of internal active substances and side reactants by high-temperature placement, and separates out batteries with large self-discharge by combining the formation and a mode of testing the OCV difference settlement twice before and after capacity grading; and simultaneously, after capacity grading, batteries with large self-discharge are sorted out again through a difference settlement mode of testing OCV twice. The high-capacity lithium battery manufactured by the method has stable voltage, good consistency and stronger economical efficiency and operability.

Detailed Description

For better understanding of the present invention, the contents of the present invention will be further clarified by the following examples in combination with comparative examples, but the contents of the present invention are not limited to only the following examples. In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the invention.

Comparative example

(2) formation: the first step is as follows: charging for 90 minutes by adopting a 0.05C constant current; the second step is that: charging for 90 minutes by adopting a 0.1C constant current; the third step: forming an upper limit protection voltage of 3.9V by adopting a 0.2C constant current;

(3) then testing OCV1 by using a tester with the voltage precision of 0.0001V, standing at the high temperature of 40-45 ℃ for 3 days, standing at the normal temperature for 12 hours, and testing OCV 2; screening out batteries with larger difference when self-discharge is less than 15mv and more than 30mv by settling the difference value between the OCV1 and the OCV 2;

(4) a capacity grading step: 0.5C constant current discharge is carried out for 2.75V; charging at 0.5C with constant current and constant voltage for 4.2V, and cutting off current for 0.01C; ③ 0.5C constant current discharge 2.75V; fourthly, charging the battery at constant current and constant voltage of 0.5C for 3.9V, and cutting off the current of 0.01C;

(5) detecting OCV3 by using a voltage and internal resistance tester with the precision of 0.0001V, testing OCV4 after standing for 7 days at normal temperature, and settling the OCV3-OCV4 to obtain qualified batteries with the settlement difference value of less than or equal to 9 mv;

and (5) preparing a qualified battery for the comparative example according to the steps (1) to (5).

Example one

(2) formation: the first step is as follows: charging for 90 minutes by adopting a 0.05C constant current; the second step is that: charging for 90 minutes by adopting a 0.1C constant current; the third step: forming an upper limit protection voltage of 4.3V by adopting a constant current of 0.3C, and cutting off the current of 0.01C;

(3) then testing OCV1 by using a tester with the voltage precision of 0.0001V, standing at the high temperature of 40-45 ℃ for 3 days, standing at the normal temperature for 12 hours, and testing OCV 2; screening out batteries with large difference of self-discharge less than 50mv and more than 65mv by settling the difference value of OCV1-OCV 2;

a qualified battery of the example was obtained according to the steps (1) to (5).

Example two

(4) a capacity grading step: 0.5C constant current discharge is carried out for 2.75V; charging at 0.5C with constant current and constant voltage for 4.2V, and cutting off current for 0.01C; ③ 0.5C constant current discharge 2.75V; and fourthly, charging for 60 minutes at constant current of 0.5C, and limiting the voltage to 4.2V.

a battery acceptable in the second example was obtained according to the steps (1) to (5).

Qualified batteries prepared in comparative example, example one and example two were precisely paired to prepare 3 strings of 1, and the batteries were circulated for 50 weeks at 3m Ω, 3mv and 20mAh, and the pressure difference and capacity retention were measured. The specific detection data are as follows:

through comparative example, comparative example I and comparative example II, the comparative example shows that the comparative example I and comparative example II show that the battery voltage of the formation voltage 4.3V is higher than that of the battery with the formation voltage 3.9V by about 0.0059V under the same standing time and temperature conditions after capacity grading, meanwhile, the capacity after circulation is kept higher by 0.2 percentage point, and the voltage range is smaller by 0.006V; in contrast to the first embodiment, under the same test conditions, the capacity of the second embodiment is maintained 0.9% higher than that of the first embodiment after the cyclic test due to the constant current charging ratio of the constant current charging to the constant current charging, and the voltage range is 0.003V smaller.

The following conclusions are drawn through comparison of detection data:

by comparing the first embodiment and the second embodiment which simultaneously increase the formation voltage to 4.3V by the small current gradient formation with the comparative formation voltage of 3.9V, the method for increasing the formation voltage by the small current with the same gradient is shown to be capable of fully intensifying the generation of side reactants in the battery, reducing the voltage difference generated in the subsequent grouping application, improving the capacity retention rate and prolonging the grouping service life. The proposal solves the consistency problem of battery grouping application to a certain extent from the source essence, and is an improvement way with simple operation, economy and practicality.

It should be noted that the above-mentioned embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.

Claims

1. A sorting method for self-discharge performance of a high-capacity lithium battery is characterized by comprising the following steps: the method comprises the following steps:

(2) and (2) forming the lithium battery in the step (1) by the following steps: the first step is as follows: charging by adopting a 0.05C constant current; the second step is that: charging by adopting a 0.1C constant current; the third step: the constant current of 0.3C is adopted for formation, the upper limit protection voltage of the constant voltage is 4.3V, and the cut-off current is 0.01C;

(4) grading the capacity of the lithium battery in the step (3) by adopting the following steps: 0.5C constant current discharge is carried out for 2.75V; charging at constant current of 0.5C, charging at constant voltage of 4.2V, and cutting off current of 0.01C; ③ 0.5C constant current discharge 2.75V; fourthly, charging for 60 minutes at constant current of 0.5C, and limiting the voltage to 4.2V;

2. The method for sorting the self-discharge performance of the high-capacity lithium battery as claimed in claim 1, wherein: in the step (2), the constant current charging time is 90 minutes in the first step and the second step.