Disclosure of Invention
The application aims to provide a method for improving capacity matching consistency of a lithium ion battery, and aims to solve the problem that in the prior art, the capacity matching consistency of the lithium ion battery is affected by the environmental temperature in the production process of the lithium ion battery.
The application is realized in such a way that the method for improving the capacity allocation consistency of the lithium ion battery comprises the following steps:
s10: charging the lithium ion battery to a full-charge state, and then placing the lithium ion battery;
s20: the ambient temperature of the lithium ion battery after being placed is T1 Step discharge of the combination of large and small currents is carried out under the condition of (1) and the discharge capacity of each stage is measured; wherein, the discharge current I in the 1 st stage1 The discharge capacity at the lower level was C1 Phase 2 discharge current I2 The discharge capacity at the lower level was C2 N-th stage discharge current In The discharge capacity at the lower level was Cn Final stage discharge current In+1 The discharge capacity at the lower level was Cn+1 ，In+1 Less than or equal to 0.01C, wherein C is the rated battery capacity of the lithium ion battery; the lithium ion battery is at the ambient temperature T1 Under the condition thatLimit discharge capacity C of (2)max ＝C1 +C2 +……+Cn +Cn+1 The method comprises the steps of carrying out a first treatment on the surface of the n is a natural number;
s30: respectively at ambient temperature T2 、T3 、……Tm And (2) repeating the steps S10-S20, and testing the limit capacity of the lithium ion battery at each environmental temperature, wherein the limit capacity of the lithium ion battery at the standard environmental temperature is marked as Cmax mark ；
S40: couple (C)max -Cmax mark )/Cn+1 T is subjected to linear fitting analysis, and the limit discharge capacity C of the lithium ion battery at standard discharge temperaturemax mark The mathematical model of (a) is: c (C)max mark ＝C1 +C2 +……+Cn +Cn+1 -Cn+1 * (a+b), a being the ambient temperature T versus the final stage discharge capacity Cn+1 B is a correction coefficient; through (C)max -Cmax mark )/Cn+1 T is subjected to linear fitting analysis, and the determined values of the coefficient a and the constant b are determined; and calculating the limit discharge capacity of the lithium ion battery at the standard ambient temperature in the mass production process through the mathematical model.
Optionally, in step 20, the lithium ion battery is left for more than 10 minutes after each stage of discharge.
Optionally, in step S20, I1 ≥I2 ≥……≥In ≥In+1 。
Alternatively, in step S40, the mathematical model is applied at a temperature range of 21 ℃ to 43 ℃.
Optionally, in step S30, the standard ambient temperature is 25 ℃.
Optionally, the discharging in the n-th stage in the step S10 is stopped when the voltage of the lithium ion battery reaches 2.5V or 2.75V.
Optionally, during the final stage discharge in the step S10, the voltage of the lithium ion battery is kept at 2.5V or 2.75V.
Optionally, before step S10, the lithium ion battery is left in a constant temperature environment with standard ambient temperature for more than 30min, and then the lithium ion battery is producedStandard charging current, constant current and constant voltage charging specified by the standard specification of the product are carried out until full power is obtained; after the material is placed for more than 10 minutes, discharging to cut-off voltage according to standard discharging current specified by product specification, and marking the discharging capacity as C0 。
Optionally, a conversion constant d=c between the limit capacity and the nominal capacity of the lithium ion batterymax mark -C0 。
Optionally, C for a plurality of said lithium ion batteriesmax mark Performing capacity allocation according to the capacity limit of 20mAh, and dividing the capacity allocation into a plurality of capacity files; sampling and detecting the lithium ion battery in each capacity range, firstly charging the battery to full power at a constant current and constant voltage of 0.5C according to the requirement of a product specification under the constant temperature environment with the ambient temperature of 25 ℃, placing the battery for more than 30 minutes, then discharging the battery to a cut-off voltage at a constant current of 0.2C, measuring the nominal capacity of the lithium ion battery, and evaluating the capacity matching consistency of the lithium ion battery.
Compared with the prior art, the method for improving the capacity allocation consistency of the lithium ion battery provided by the application has the advantages that the environmental temperature is T1 Under the condition of (1) carrying out discharge detection on the lithium ion battery to be detected with extremely small discharge current, thereby measuring the limit discharge capacity C of the lithium ion batterymax And then, determining a mathematical model through fitting analysis of the limit discharge capacities of the batteries at different temperatures, converting the mathematical model into the limit discharge capacities of the lithium ion batteries at standard discharge temperatures, and facilitating capacity allocation according to the capacity, reducing the influence of environmental temperature difference on the capacities of the lithium ion batteries in the production process, and remarkably improving the consistency of capacity allocation. The technical scheme provided by the embodiment ensures that the production enterprises do not need to additionally increase the investment of complex refrigeration constant temperature equipment, reduces the higher energy consumption cost generated by strict environmental temperature difference control, and is suitable for large-scale application of lithium ion battery production enterprises to battery capacity allocation.
In the embodiment, through a multi-step discharging mode combining large-current discharging and small-current discharging, and adopting extremely small-current discharging in the final stage, the method can not only not affect the production efficiency of battery detection, but also obviously reduce the influence of environmental temperature difference on the limit discharge capacity of the battery, greatly reduce the control difficulty of the environmental temperature of enterprises, and simultaneously realize the targets of three aspects of capacity allocation consistency, production efficiency improvement and energy consumption cost reduction.
Detailed Description
The present application will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present application more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application.
The implementation of the present application will be described in detail below with reference to specific embodiments.
The same or similar reference numerals in the drawings of the present embodiment correspond to the same or similar components; in the description of the present application, it should be understood that, if there is an azimuth or positional relationship indicated by terms such as "upper", "lower", "left", "right", etc., based on the azimuth or positional relationship shown in the drawings, it is only for convenience of describing the present application and simplifying the description, but it is not indicated or implied that the apparatus or element referred to must have a specific azimuth, be constructed and operated in a specific azimuth, and thus terms describing the positional relationship in the drawings are merely illustrative and should not be construed as limiting the present application, and specific meanings of the terms described above may be understood by those of ordinary skill in the art according to specific circumstances.
In the prior art, the capacity of a lithium ion battery is usually tested according to a test method in a specification or a product specification, the discharge current of the battery is larger in the test process, and the environmental temperature has a remarkable influence on the discharge capacity test of the battery, so that the tolerance of the assembled lithium ion battery is larger, and the overall performance of the lithium ion battery is influenced. In order to control the environmental temperature, a complex constant temperature control system is required to be added, a large amount of energy is required to be consumed for maintaining the constant temperature, and the production cost of the product is increased. Therefore, the inventor faces the technical problem actually generated in the production practice, researches a method for improving the capacity matching consistency of the lithium ion battery, and is applied to the production practice, so that the yield of the lithium ion battery is greatly improved.
Referring to fig. 1-3, a preferred embodiment of the present application is provided.
A method for improving capacity allocation consistency of lithium ion batteries comprises the following steps:
s10: charging the lithium ion battery to a full-charge state, and then placing the lithium ion battery;
s20: for the lithium ion battery after being placed, the ambient temperature is T1 Step discharge of the combination of large and small currents is carried out under the condition of (1) and the discharge capacity of each stage is measured; wherein, the discharge current I in the 1 st stage1 The discharge capacity at the lower level was C1 Phase 2 discharge current I2 The discharge capacity at the lower level was C2 N-th stage discharge current In The discharge capacity at the lower level was Cn Final stage discharge current In+1 The discharge capacity at the lower level was Cn+1 ，In+1 Less than or equal to 0.01C, wherein C is the rated battery capacity of the lithium ion battery; lithium ion battery at ambient temperature T1 Limiting discharge capacity C under conditionsmax ＝C1 +C2 +……+Cn +Cn+1 The method comprises the steps of carrying out a first treatment on the surface of the n is a natural number;
s30: respectively at ambient temperature T2 、T3 、……Tm And (2) repeating the steps S10-S20, and testing the limit capacity of the lithium ion battery at each environmental temperature, wherein the limit capacity of the lithium ion battery at the standard environmental temperature is marked as Cmax mark ；
S40: couple (C)max -Cmax mark )/Cn+1 T is subjected to linear fitting analysis, and the limit discharge capacity C of the lithium ion battery at standard discharge temperaturemax mark The mathematical model of (a) is: c (C)max mark ＝C1 +C2 +……+Cn +Cn+1 -Cn+1 * (a+b), a being the ambient temperature T versus the final stage discharge capacity Cn+1 B is a correction coefficient; through (C)max -Cmax mark )/Cn+1 T is subjected to linear fitting analysis, and the determined values of the coefficient a and the constant b are determined; and calculating the limit discharge capacity of the lithium ion battery at the standard ambient temperature in the mass production process through a mathematical model.
The method for improving capacity allocation consistency of lithium ion batteries provided by the embodiment is implemented by using the temperature T at the ambient temperature1 Under the condition of (1) carrying out discharge detection on the lithium ion battery to be detected with extremely small discharge current, thereby measuring the limit discharge capacity C of the lithium ion batterymax And then, determining a mathematical model through fitting analysis of the limit discharge capacities of the batteries at different temperatures, converting the mathematical model into the limit discharge capacities of the lithium ion batteries at standard discharge temperatures, and facilitating capacity allocation according to the capacity, reducing the influence of environmental temperature difference on the capacities of the lithium ion batteries in the production process, and remarkably improving the consistency of capacity allocation. The technical scheme provided by the embodiment ensures that the production enterprises do not need to additionally increase the investment of complex refrigeration constant temperature equipment, reduces the higher energy consumption cost generated by strict environmental temperature difference control, and is suitable for large-scale application of lithium ion battery production enterprises to battery capacity allocation.
In the embodiment, through a multi-step discharging mode combining large-current discharging and small-current discharging, and adopting extremely small-current discharging in the final stage, the method can not only not affect the production efficiency of battery detection, but also obviously reduce the influence of environmental temperature difference on the limit discharge capacity of the battery, greatly reduce the control difficulty of the environmental temperature of enterprises, and simultaneously realize the targets of three aspects of capacity allocation consistency, production efficiency improvement and energy consumption cost reduction.
In step 20, the lithium ion battery is left for more than 10 minutes after each stage of discharge. The heat release of the battery during discharging is reduced to adversely affect the capacity detection of the lithium ion battery.
In step S20, I1 ≥I2 ≥……≥In ≥In+1 . Through the multi-step discharging mode combining large-current discharging and small-current discharging, the rapid discharging can be realized through the large-current discharging, the production efficiency is improved, and the limit capacity of the single battery can be measured more accurately through the subsequent small-current discharging and the minimum-current discharging.
Specifically, the discharge current I of each discharge stage before the final stage1 、I2 、……、In The magnitude of (2) depends on any discharge current which can be borne by the lithium ion battery, and can be generally 0.2-100 ℃; and the minimum discharge current value I of the final stagen+1 Less than or equal to 0.01C and as small as the equipment accuracy permits.
Where C is the design capacity of the lithium ion battery, and if C is 1000mAh, the minimum discharge current of 0.01C means 10mA.
In step S30, at the ambient temperature T2 、T3 、……Tm And (3) m is a natural number, repeating the steps S10-S20, and testing the limit capacity of the lithium ion battery at each ambient temperature. In the measuring process, the standard test method of the design, materials, structures, production process and product capacity of the lithium ion battery product is kept unchanged, and the pertinence, the accuracy and the effectiveness of a mathematical model obtained later are ensured. For different types of lithium ion batteries, the method for improving the capacity allocation consistency of the lithium ion batteries is adopted, and mathematical models for capacity calibration are established respectively.
Referring to the cumulative discharge capacity increase rate of the lithium ion battery at different temperatures shown in fig. 3, under the condition of standard discharge current of 0.2C, the temperature difference has a larger influence on the cumulative discharge capacity of the lithium ion battery; the larger the discharge current is, the larger the temperature difference has an effect on the accumulated discharge capacity of the lithium ion battery; and under the condition of discharging at the minimum current of 0.01C, the temperature difference has little influence on the accumulated discharge capacity of the lithium ion battery, and the curve of the accumulated discharge capacity increase rate of the lithium ion battery at different temperatures is basically horizontal.
In step S30, the standard ambient temperature is 25 ℃. Corresponding to standard environmental temperature when the battery national standard/enterprise standard/product specification is tested.
Specifically, in step S40, the temperature range for which the mathematical model is applied is 21 ℃ to 43 ℃. For example, the limit capacities of the batteries at the respective temperatures of 21 ℃, 23 ℃, 25 ℃, 27 ℃, 29 ℃, 31 ℃, 33 ℃, 35 ℃, 37 ℃, 39 ℃, 41 ℃ and 43 ℃ can be tested, and the mathematical model in step S40 can be constructed.
In step S10, the n-th stage discharge is stopped when the voltage of the lithium ion battery reaches 2.5V or 2.75V.
At the final stage of discharge in step S10, the voltage of the lithium ion battery is maintained at 2.5V or 2.75V.
In the discharging process, the lithium ion battery can only be discharged to the termination voltage, and the termination voltage can be 2.5V or 2.75V generally; the lithium ion battery cannot be discharged to zero volt, otherwise, irreversible loss of partial electric quantity of the lithium ion battery is caused, and the battery is seriously and thoroughly damaged.
Before step S10, placing the lithium ion battery in a constant temperature environment with standard environmental temperature for more than 30min, and then charging the lithium ion battery to full power by constant current and constant voltage with standard charging current specified by a product specification; after the material is placed for more than 10 minutes, discharging to cut-off voltage according to standard discharging current specified by product specification, and marking the discharging capacity as C0 . The situation of detecting the lithium ion battery by a buyer is simulated, and the situation corresponds to the nominal capacity of the battery in the national standard/enterprise standard/product specification test.
Conversion constant d=c between limit capacity and nominal capacity of lithium ion batterymax mark -C0 . The conversion constant d can be determined through the detection experiment operation steps in the application, so that capacity matching is conveniently carried out on a plurality of lithium ion batteries.
Preferably, C for a plurality of lithium ion batteriesmax mark And performing capacity allocation according to the capacity limit of 20mAh, and dividing the capacity allocation into a plurality of capacity files. The consistency of the capacity allocation of the lithium ion battery of each capacity grade is good.
Sampling and detecting the lithium ion battery in each capacity range, firstly charging the battery to full power at a constant current and constant voltage of 0.5C according to the requirement of a product specification under the constant temperature environment with the ambient temperature of 25 ℃, placing the battery for more than 30 minutes, then discharging the battery to a cut-off voltage at a constant current of 0.2C, measuring the nominal capacity of the lithium ion battery, and evaluating the capacity matching consistency of the lithium ion battery. Through sampling detection, the consistency of capacity allocation of the lithium ion battery can be determined again to meet the requirements of the yield of production enterprises.
In the following specific examples, specific operations and experimental results of a method for improving capacity allocation consistency of lithium ion batteries provided by the application are described.
First embodiment:
the detection object is: the 18650 lithium ion battery has a design capacity of 2600mAh, and comprises a ternary material of nickel cobalt lithium aluminate of an anode, graphite of a cathode, hexafluorophosphate lithium electrolyte, a diaphragm, a steel shell and other key materials, wherein the basic principle is that the anode is delithiated and intercalated with graphite of the cathode during charging, and the graphite of the cathode is delithiated and intercalated with lithium ions during discharging and returns to the anode material.
A method for improving capacity allocation consistency of lithium ion batteries comprises the following steps:
1) Taking 8pcs (pcs is an abbreviation of pieces, refers to a number, a number of pieces, a plural number of pieces)
The batteries are respectively placed in a constant temperature environment at 25 ℃ for 30min, then are charged to 4.2V according to the constant current and constant voltage of 0.5C required by the specification of the product, and the cut-off current is 0.02C;
2) After the mixture is placed for 10min, the mixture is discharged to 2.75V according to the standard discharge current of 0.2C specified by the product specification, and the discharge capacity is marked as C0 ；
3) Recharging the battery to 4.2V according to the method in step 1, discharging to 2.75V by 1.0C, 0.2C, 0.1C, 0.05C, 0.02C and 0.01C with minimum current respectively, wherein after each discharge step is finished, the battery is left for 10min, and the discharge capacity of each discharge step is marked as C respectively1 、C2 、C3 、C4 、C5 And C6 Limit capacity Cmax ＝C1 +C2 +C3 +C4 +C5 +C6 ；
4) Repeating steps 1-3 to test the limit capacity C of the battery at each temperature at 21 deg.C, 23 deg.C, 25 deg.C, 27 deg.C, 29 deg.C, 31 deg.C, 33 deg.C, 35 deg.C, 37 deg.C, 39 deg.C, 41 deg.C and 43 deg.Cmax Wherein the limit capacity at 25℃is recorded asCmax mark ；
5) With (C)max -Cmax mark ) And performing fitting analysis on the (C6-T) to obtain a mathematical transformation model for testing the limit capacity of the lithium ion battery at 25 ℃ of the model: c (C)max mark ＝C1 +C2 +C3 +C4 +C5 +C6 -C6 *
(0.1648 x T-4.151), the applicable temperature range is preferably 21 ℃ or less and T or less than 43 ℃;
6) C calculated from the C0 measured in step 2 and the mathematical model in step 5max mark The conversion constant d=c of the lithium ion limit capacity and nominal capacity of the model can be calculatedmax mark -C0 ；
7) The capacity test of lithium ion battery batch production is completed according to the charge and discharge steps shown in the table 1, and the battery of the model is discharged to the limit capacity C of 2.75V at the temperature of 25 ℃ under the full charge of 4.2Vmax mark ＝
C1+c2+c3+c4+c5+c6-c6 (0.1648×t-4.151), conversion constant d=140 for the limit capacity and nominal capacity, discharging from 4.2V full charge at 0.2C to nominal capacity C of 2.75V as required by the specificationLabel (C) ＝Cmax mark -140, the ambient temperature is more than or equal to 21 ℃ and less than or equal to 43 ℃.
Table 118650 capacity batch test charge-discharge process steps
8) Minimum capacity C of 0.2C discharge of the type battery according to the requirements of the product specificationLabel (C) More than or equal to 2550mAh, then Cmax mark The capacity matching is carried out according to the capacity extremely poor of 20mAh, 100pcs batteries of three capacity grades are extracted, the batteries are firstly charged to 4.2V (cut-off current 0.02C) at constant current and constant voltage of 0.5C according to the requirement of a product specification under the constant temperature environment with the environment temperature of 25 ℃, then discharged to 2.75V at constant current of 0.2C, the nominal capacities of three groups of batteries are all more than or equal to 2550mAh, the tolerance of the three groups of batteries is less than 1.5%, and the tolerance of the three groups of batteries is respectively 32mAh, 37mAh and 31mAh, so that the extremely good effect is achieved, and the capacity matching consistency of the lithium ion batteries is remarkably improved.
Specific embodiment II:
the detection object is: the 18650 lithium ion battery has a design capacity of 3350mAh, and comprises a positive electrode nickel cobalt aluminum material, a negative electrode graphite, hexafluorophosphate lithium electrolyte, a diaphragm, a steel shell and other key materials, wherein the basic principle is that the positive electrode is delithiated and intercalated into the negative electrode graphite during charging, and the negative electrode graphite is delithiated and intercalated into the positive electrode material during discharging.
A method for improving capacity allocation consistency of lithium ion batteries comprises the following steps:
1) Taking 8pcs batteries, respectively placing the 8pcs batteries in a constant temperature environment at 25 ℃ for 30min, then charging the 8pcs batteries to 4.2V according to the constant current and constant voltage of 0.5C required by the specification of the product, and stopping the current at 0.02C;
2) After the mixture is placed for 10min, the mixture is discharged to 2.5V according to the standard discharge current of 0.2C specified by the product specification, and the discharge capacity is marked as C0 ；
3) Recharging the battery to 4.2V according to the method in step 1, discharging to 2.5V by 1.0C, 0.2C, 0.1C, 0.05C, 0.02C and 0.01C with minimum current respectively, wherein the rest time is 10min after the discharge is finished, and the discharge capacity of each step is marked as C respectively1 、C2 、C3 、C4 、C5 And C6 Limit capacity Cmax ＝C1 +C2 +C3 +C4 +C5 +C6 ；
4) Repeating steps 1-3 to test the limit capacity C of the battery at each temperature at 21 deg.C, 23 deg.C, 25 deg.C, 27 deg.C, 29 deg.C, 31 deg.C, 33 deg.C, 35 deg.C, 37 deg.C, 39 deg.C, 41 deg.C and 43 deg.Cmax Wherein the limiting capacity at 25℃is designated Cmax mark ；
5) With (C)max -Cmax mark ) And C6-T is subjected to fitting analysis, and a mathematical transformation model of the model lithium ion battery for testing the limit capacity at 25 ℃ is as follows: c (C)max mark ＝C1 +C2 +C3 +C4 +C5 +C6 -C6 *
(2.814-0.1067 x T), the applicable temperature range is preferably 21 ℃ or more and less than or equal to 43 ℃;
6) C measured according to step 20 And step 5 mathematical model calculationC of (2)max mark The conversion constant d=c of the lithium ion limit capacity and nominal capacity of the model can be calculatedmax mark -C0 ；
7) The capacity test of lithium ion battery batch production is completed according to the charge and discharge steps shown in the table 2, and the battery of the model is discharged to the limit capacity C of 2.5V at the full charge of 4.2V under the condition of 25 DEG Cmax mark ＝
Conversion constants d=64 for the limit capacity and nominal capacity of c1+c2+c3+c4+c5+c6-c6 (2.814-0.1067×t), discharge from 4.2V full charge at 0.2C to nominal capacity C of 2.5V as required by the specificationLabel (C) ＝Cmax mark -64, the ambient temperature is more than or equal to 21 ℃ and less than or equal to 43 ℃.
Table 218650 capacity batch test charge-discharge process step
8) Minimum capacity C of 0.2C discharge of the type battery according to the requirements of the product specificationLabel (C) ≥
3250mAh, then Cmax mark Performing capacity matching according to the capacity difference of 20mAh, extracting 100pcs batteries with A, B, C capacity files, and charging the batteries to 4.2V (cut-off current) at constant current and constant voltage of 0.5C under the constant temperature environment with the environment temperature of 25 ℃ according to the requirement of the product specification
0.02C), then discharging to 2.5V at constant current of 0.2C, and the nominal capacities of the three groups of batteries are equal to or more than
3250mAh, and the tolerance in the three groups of battery packs is less than 2% and is 46mAh, 41mAh and respectively
42mAh, achieves a very good effect, and remarkably improves the capacity allocation consistency of the lithium ion battery.
The method for improving the capacity allocation consistency of the lithium ion battery provided by the embodiment can be applied to the capacity measurement process of the lithium ion battery, and of course, the method can also be applied to the capacity measurement process of other batteries, and is not limited to the application in the embodiment.
The foregoing description of the preferred embodiments of the application is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the application.