A method for improving the accuracy of lithium-ion battery capacity division

Abstract

This invention belongs to the field of lithium-ion battery manufacturing technology, and relates to a method for improving the accuracy of capacity grading in lithium-ion batteries. The method includes controlling the ambient temperature range of the lithium-ion battery during the capacity grading stage, performing constant current and constant voltage full charging of the lithium-ion battery, discharging the lithium-ion battery with gradually decreasing current to the final voltage, performing a first compensation of the lithium-ion battery capacity based on the relationship between lithium-ion battery capacity and ambient temperature, and then performing a second compensation of the lithium-ion battery capacity based on the relationship between lithium-ion battery discharge current and capacity. This invention can improve the accuracy of lithium-ion battery capacity grading, resulting in higher capacity consistency when lithium-ion batteries are used in combination, avoiding overcharging and over-discharging of some batteries during the charging and discharging process due to large capacity differences, thus extending the lifespan of the lithium-ion battery pack and reducing safety risks.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery manufacturing process, and in particular relates to a method for improving the accuracy of lithium ion battery capacity division. Background Art

[0002] Lithium-ion batteries are a type of battery that is currently commonly used and are widely used in digital products, power tools, automobiles, energy storage and other fields. In many of these fields, multiple batteries are used in series and parallel combination, and at this time, high requirements are placed on the consistency of battery capacity in the same battery pack. If the battery capacity varies greatly, some batteries will be overcharged or over-discharged during the charging and discharging process, which will greatly shorten the life of the battery pack and may even cause combustion and explosion in severe cases. In existing lithium-ion battery capacity division methods, the capacity is greatly affected by ambient temperature. During mass production, the battery capacity division environment has a large space, and it is difficult to ensure consistent temperature in the horizontal and vertical directions, resulting in a large deviation between the capacity obtained by battery capacity division and the actual capacity of the battery, that is, the capacity division is inaccurate, and the risk of shortened battery life and combustion and explosion is high during subsequent combined use. Summary of the invention

[0003] The purpose of the invention is to provide a method for improving the accuracy of lithium-ion battery capacity division, making the capacity division more accurate, reducing the capacity difference of single cells during combined use, increasing the life of the battery pack, and reducing safety risks.

[0004] The present invention adopts the following technical scheme to achieve the above-mentioned purpose, a method for improving the accuracy of lithium-ion battery capacity classification, and the specific steps are:

[0005] Step S1, before lithium-ion battery capacity division, controlling the temperature of the capacity division environment;

[0006] Step S2, after the ambient temperature meets the standard requirements, connect the lithium-ion battery to the charging and discharging equipment, fully charge the lithium-ion battery in a 0.5C-1C constant current and constant voltage mode, and the constant voltage end current is 0.02-0.05C (current rate); let it stand for 10-20 minutes after charging; discharge at a constant current of current 1 to the end voltage; let it stand for 3-5 minutes; discharge at a constant current of current 2 to the end voltage; let it stand for 3-5 minutes; discharge at a constant current of current 3 to the end voltage; let it stand for 3-5 minutes; discharge at a constant current of current 4 to the end voltage; let it stand for 3-5 minutes; discharge at a constant current of current 5 to the end voltage; during the capacity division process, the equipment automatically measures and records the ambient temperature; wherein the current of current step 1 to current step 5 gradually decreases;

[0007] Step S3, counting the sum of the capacities of each step of the constant current discharge in step S2;

[0008] Step S4, performing the first temperature compensation on the battery capacity;

[0009] Step S5, performing a second compensation on the battery capacity, this compensation is to compensate for the capacity difference caused by the different discharge currents.

[0010] In the above method for improving the accuracy of lithium-ion battery capacity classification, in step S1, the ambient temperature is 20-40°C.

[0011] In the above method for improving the accuracy of lithium-ion battery capacity classification, in step S1, the ambient temperature is 20-35°C.

[0012] In the above method for improving the accuracy of lithium-ion battery capacity classification, in step S2, the range of current 1 is 0.5-2C, the range of current 2 is 0.2-0.5C, the range of current 3 is 0.1-0.2C, the range of current 4 is 0.05-0.1C, and the range of current 5 is 0.02-0.05C.

[0013] In the above-mentioned method for improving the accuracy of lithium-ion battery capacity division, in step S4, the first temperature compensation of the battery capacity is to call out the ambient temperature data of the capacity division process from the system, and the system automatically calculates the difference between the actual ambient temperature and the standard ambient temperature, and then performs the first temperature compensation on the battery capacity based on the relationship coefficient between the capacity and the temperature.

[0014] In the above method for improving the accuracy of lithium-ion battery capacity classification, in step S4, the coefficient of relationship between capacity and temperature is in the range of 0%-1% SOC / °C.

[0015] In the above method for improving the accuracy of lithium-ion battery capacity classification, in step S5, the second compensation of the battery capacity is performed by the system automatically according to a pre-set current and capacity relationship.

[0016] In the above method for improving the accuracy of lithium-ion battery capacity classification, in step S5, the coefficient of relationship between capacity and current ranges from 0% to 5% SOC.

[0017] The beneficial effects of the present invention are as follows: the present invention can improve the accuracy of the capacity of lithium-ion batteries, so that the lithium-ion batteries have higher capacity consistency when used in combination, avoid overcharging and over-discharging of some batteries during the charging and discharging process of the battery pack due to large capacity differences, extend the life of the lithium-ion battery pack, and reduce safety risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a flow chart of the method of the present invention.

[0019] Figure 2 This is a capacity comparison chart between the G method and the customer's standard method. DETAILED DESCRIPTION

[0020] The above contents of the present invention are further described in detail below through examples, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples, and all technologies implemented based on the above contents of the present invention belong to the scope of the present invention.

[0021] Example 1

[0022] The above contents of the present invention are further described in detail below in conjunction with the accompanying drawings. Figure 1 As shown, taking a 18650-2.0Ah nickel-cobalt-manganese ternary lithium-ion battery as an example, a method for improving the accuracy of lithium-ion battery capacity distribution in this embodiment specifically includes the following steps:

[0023] Step S1, before lithium-ion battery capacity division, control the temperature of the capacity division environment to be between 20°C and 35°C;

[0024] Step S2, after the ambient temperature meets the standard requirements, connect the lithium-ion battery to the charging and discharging equipment, charge the lithium-ion battery to 4.2V in a 1A constant current and constant voltage mode, and the constant voltage end current is 0.04A; let it stand for 10 minutes after charging; discharge at a constant current of 2A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 0.4A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 0.2A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 0.1A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 0.04A to an end voltage of 2.5V; during the capacity division process, the equipment automatically measures and records the ambient temperature;

[0025] Step S3, the sum of the capacities of each step of the constant current discharge in step S2 is counted as (2086 mAh);

[0026] Step S4, the system retrieves the starting ambient temperature data of the 2A discharge step in the capacity division process, and the system automatically calculates the difference between the actual ambient temperature and the standard ambient temperature of 25°C, and then performs temperature compensation on the battery capacity according to the capacity-temperature relationship coefficient of 0.06%SOC / °C (corresponding to 1.2mAh / °C in this implementation case);

[0027] In step S5, the system automatically compensates the battery capacity according to the pre-set current and capacity relationship 2% SOC (corresponding to 40 mAh in this implementation case).

[0028] Combined with steps S3, S4, and S5, the overall battery capacity compensation formula is: C=C0-(T-25)×ab, where C is the battery capacity after compensation, C0 is the sum of the capacities of each step of constant current discharge in step S3, T is the starting ambient temperature of the 2A discharge step in the capacity division process in step S4, a is the coefficient of the relationship between capacity and temperature in step S3, 1.2mAh / ℃, and b is the relationship between current and capacity in step S5, 40mAh. According to the above formula, the battery capacity C after compensation in this embodiment is (2041mAh), and the capacity is 2038mAh tested according to the standard method in the product specification, with a small deviation.

[0029] Comparative Example 1

[0030] Take 18650-2.0Ah nickel-cobalt-manganese ternary lithium-ion battery as an example.

[0031] Step S1, before lithium-ion battery capacity division, control the temperature of the capacity division environment to be between 20°C and 35°C;

[0032] Step S2, after the ambient temperature meets the standard requirements, connect the lithium-ion battery to the charging and discharging equipment, charge the lithium-ion battery to 4.2V in a 1A constant current and constant voltage mode, and the constant voltage end current is 0.04A; let it stand for 10 minutes after charging; discharge it at a constant current of 2A to an end voltage of 2.5V; let it stand for 5 minutes; discharge it at a constant current of 0.4A to an end voltage of 2.5V; during the capacity division process, the equipment automatically measures and records the ambient temperature;

[0033] Step S3, counting the sum of the capacities of each step of the constant current discharge in step S2 (2046 mAh);

[0034] Step S4, the system retrieves the starting ambient temperature data of the 2A discharge step in the capacity division process, and the system automatically calculates the difference between the actual ambient temperature and the standard ambient temperature of 25°C, and then performs temperature compensation on the battery capacity according to the capacity-temperature relationship coefficient of 0.4%SOC / °C (corresponding to 8mAh / °C in this implementation case);

[0035] Combined with steps S3 and S4, the overall battery capacity compensation formula is: C=C0-(T-25)×a, where C is the battery capacity after compensation, C0 is the sum of the capacities of each step of constant current discharge in step S3, T is the starting ambient temperature of the 2A discharge step in the capacity division process in step S4, and a is the coefficient of the relationship between capacity and temperature in step S3, 1.2mAh / ℃. According to the above formula, the battery capacity C after compensation in this embodiment is (2014mAh), and the capacity is 2042mAh tested according to the standard method in the product specification, which has a large deviation.

[0036] Example 2

[0037] The above contents of the present invention are further described in detail below in conjunction with the accompanying drawings. Figure 1As shown, taking a 14500-0.68Ah nickel-cobalt-manganese ternary lithium-ion battery as an example, a method for improving the accuracy of lithium-ion battery capacity distribution in this embodiment specifically includes the following steps:

[0038] Step S1, before lithium-ion battery capacity division, control the temperature of the capacity division environment to be between 20°C and 35°C;

[0039] Step S2, after the ambient temperature meets the standard requirements, connect the lithium-ion battery to the charging and discharging equipment, charge the lithium-ion battery to 4.2V in a constant current and constant voltage mode of 0.34A, and the constant voltage end current is 0.013A; let it stand for 10 minutes after charging; discharge at a constant current of 1C to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 0.136A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 0.068A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 0.034A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 0.013A to an end voltage of 2.5V; during the capacity division process, the equipment automatically measures and records the ambient temperature;

[0040] Step S3, the sum of the capacities of each step of the constant current discharge in step S2 is counted as (715 mAh);

[0041] Step S4, the system retrieves the starting ambient temperature data of the 0.68A discharge step in the capacity division process, and the system automatically calculates the difference between the actual ambient temperature and the standard ambient temperature of 25°C, and then performs temperature compensation on the battery capacity according to the capacity-temperature relationship coefficient of 0.06%SOC / °C (corresponding to 0.41mAh / °C in this implementation case);

[0042] In step S5, the system automatically compensates the battery capacity according to the pre-set current and capacity relationship 2% SOC (corresponding to 13 mAh in this implementation case).

[0043] Combined with steps S3, S4, and S5, the overall battery capacity compensation formula is: C=C0-(T-25)×ab, where C is the battery capacity after compensation, C0 is the sum of the capacities of each step of constant current discharge in step S3, T is the starting ambient temperature of the 1C discharge step in the capacity division process in step S4, a is the coefficient of the relationship between capacity and temperature in step S3, 0.41mAh / ℃, and b is the relationship between current and capacity in step S5, 13mAh. According to the above formula, the battery capacity C after compensation in this embodiment is (701mAh), and the capacity is 703mAh tested according to the standard method in the product specification, with a small deviation.

[0044] Comparative Example 2

[0045] Step S1, before lithium-ion battery capacity division, control the temperature of the capacity division environment to be between 20°C and 35°C;

[0046] Step S2, after the ambient temperature meets the standard requirements, connect the lithium-ion battery to the charging and discharging equipment, charge the lithium-ion battery to 4.2V in a constant current and constant voltage mode of 0.34A, and the constant voltage end current is 0.013A; let it stand for 10 minutes after charging; discharge it at a constant current of 1C to an end voltage of 2.5V; let it stand for 5 minutes; discharge it at a constant current of 0.136A to an end voltage of 2.5V; during the capacity division process, the equipment automatically measures and records the ambient temperature;

[0047] Step S3, the sum of the capacities of each step of the constant current discharge in step S2 is counted as (688 mAh);

[0048] Step S4, the system retrieves the starting ambient temperature data of the 0.68A discharge step in the capacity division process, and the system automatically calculates the difference between the actual ambient temperature and the standard ambient temperature of 25°C, and then performs temperature compensation on the battery capacity according to the capacity-temperature relationship coefficient of 0.3%SOC / °C (corresponding to 2mAh / °C in this implementation case);

[0049] Combined with steps S3 and S4, the overall battery capacity compensation formula is: C=C0-(T-25)×a, where C is the battery capacity after compensation, C0 is the sum of the capacities of each step of constant current discharge in step S3, T is the starting ambient temperature of the 1C discharge step in the capacity division process in step S4, and a is the coefficient of the relationship between capacity and temperature in step S3, 0.41mAh / ℃. According to the above formula, the battery capacity C after compensation in this embodiment is (684mAh), and the capacity is 699mAh tested according to the standard method in the product specification, which has a large deviation.

[0050] Example 3

[0051] The above contents of the present invention are further described in detail below in conjunction with the accompanying drawings. Figure 1 As shown, taking a 2590150-40Ah nickel-cobalt-manganese ternary lithium-ion battery as an example, a method for improving the accuracy of lithium-ion battery capacity distribution in this embodiment specifically includes the following steps:

[0052] Step S1, before lithium-ion battery capacity division, control the temperature of the capacity division environment to be between 20°C and 35°C;

[0053] Step S2, after the ambient temperature meets the standard requirements, connect the lithium-ion battery to the charging and discharging equipment, charge the lithium-ion battery to 4.2V in a 20A constant current and constant voltage mode, and the constant voltage end current is 0.8A; let it stand for 10 minutes after charging; discharge at a constant current of 40A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 8A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 4A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 2A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 0.8A to an end voltage of 2.5V; during the capacity division process, the equipment automatically measures and records the ambient temperature;

[0054] Step S3, the sum of the capacities of each step of the constant current discharge in step S2 is counted as (42.7Ah);

[0055] Step S4, the system retrieves the starting ambient temperature data of the 40A discharge step in the capacity division process, and the system automatically calculates the difference between the actual ambient temperature and the standard ambient temperature of 25°C, and then performs temperature compensation on the battery capacity according to the capacity-temperature relationship coefficient of 0.06%SOC / °C (corresponding to 24mAh / °C in this implementation case);

[0056] In step S5, the system automatically compensates the battery capacity according to the pre-set current and capacity relationship 2% SOC (corresponding to 800 mAh in this implementation case).

[0057] Combined with steps S3, S4, and S5, the overall battery capacity compensation formula is: C=C0-(T-25)×ab, where C is the battery capacity after compensation, C0 is the sum of the capacities of each step of constant current discharge in step S3, T is the starting ambient temperature of the 1C discharge step in the capacity division process in step S4, a is the coefficient of the relationship between capacity and temperature in step S3, 24mAh / ℃, and b is the relationship between current and capacity in step S5, 800mAh. According to the above formula, the battery capacity C after compensation in this embodiment is (41.66Ah), and the capacity is 41.57Ah tested according to the standard method in the product specification, with a small deviation.

[0058] Comparative Example 3

[0059] Take 2590150-40Ah nickel-cobalt-manganese ternary lithium-ion battery as an example.

[0060] Step S1, before lithium-ion battery capacity division, control the temperature of the capacity division environment to be between 20°C and 35°C;

[0061] Step S2, after the ambient temperature meets the standard requirements, connect the lithium-ion battery to the charging and discharging equipment, charge the lithium-ion battery to 4.2V in a constant current and constant voltage mode of 20A, and the constant voltage end current is 0.8A; let it stand for 10 minutes after charging; discharge it at a constant current of 40A to an end voltage of 2.5V; let it stand for 5 minutes; discharge it at a constant current of 8A to an end voltage of 2.5V; during the capacity division process, the equipment automatically measures and records the ambient temperature;

[0062] Step S3, the sum of the capacities of each step of the constant current discharge in step S2 is (41.62Ah);

[0063] Step S4, the system retrieves the starting ambient temperature data of the 40A discharge step in the capacity division process, and the system automatically calculates the difference between the actual ambient temperature and the standard ambient temperature of 25°C, and then performs temperature compensation on the battery capacity according to the capacity-temperature relationship coefficient of 0.3%SOC / °C (corresponding to 120mAh / °C in this implementation case);

[0064] Combined with steps S3 and S4, the overall battery capacity compensation formula is: C=C0-(T-25)×a, where C is the battery capacity after compensation, C0 is the sum of the capacities of each step of constant current discharge in step S3, T is the starting ambient temperature of the 1C discharge step in the capacity division process in step S4, and a is the coefficient of the relationship between capacity and temperature in step S3, 24mAh / ℃. According to the above formula, the battery capacity C after compensation in this embodiment is (40.42Ah), and the capacity is 41.52Ah tested according to the standard method in the product specification, which has a large deviation.

[0065] Example 4

[0066] The above contents of the present invention are further described in detail below in conjunction with the accompanying drawings. Figure 1 As shown, taking a 27130150-50Ah lithium iron phosphate lithium-ion battery as an example, a method for improving the accuracy of lithium-ion battery capacity distribution in this embodiment specifically includes the following steps:

[0067] Step S1, before lithium-ion battery capacity division, control the temperature of the capacity division environment to be between 20°C and 35°C;

[0068] Step S2, after the ambient temperature meets the standard requirements, connect the lithium-ion battery to the charging and discharging equipment, charge the lithium-ion battery to 4.2V in a constant current and constant voltage mode of 25A, and the constant voltage end current is 1A; let it stand for 10 minutes after charging; discharge at a constant current of 50A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 10A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 5A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 5A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 2.5A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 1A to an end voltage of 2.5V; during the capacity division process, the equipment automatically measures and records the ambient temperature;

[0069] Step S3, the sum of the capacities of each step of the constant current discharge in step S2 is counted as (52.9Ah);

[0070] Step S4, the system retrieves the starting ambient temperature data of the 50A discharge step in the capacity division process, and the system automatically calculates the difference between the actual ambient temperature and the standard ambient temperature of 25°C, and then performs temperature compensation on the battery capacity according to the capacity-temperature relationship coefficient of 0.06%SOC / °C (corresponding to 30mAh / °C in this implementation case);

[0071] In step S5, the system automatically compensates the battery capacity according to the pre-set current and capacity relationship 2% SOC (corresponding to 1000 mAh in this implementation case).

[0072] Combined with steps S3, S4, and S5, the overall battery capacity compensation formula is: C=C0-(T-25)×ab, where C is the battery capacity after compensation, C0 is the sum of the capacities of each step of constant current discharge in step S3, T is the starting ambient temperature of the 1C discharge step in the capacity division process in step S4, a is the coefficient of the relationship between capacity and temperature in step S3, 30mAh / ℃, and b is the relationship between current and capacity in step S5, 1000mAh. According to the above formula, the battery capacity C after compensation in this embodiment is (51.53Ah), and the capacity is 51.5Ah tested according to the standard method in the product specification, with a small deviation.

[0073] Comparative Example 4

[0074] Step S1, before lithium-ion battery capacity division, control the temperature of the capacity division environment to be between 20°C and 35°C;

[0075] Step S2, after the ambient temperature meets the standard requirements, connect the lithium-ion battery to the charging and discharging equipment, charge the lithium-ion battery to 4.2V in a constant current and constant voltage mode of 25A, and the constant voltage end current is 1A; let it stand for 10 minutes after charging; discharge it at a constant current of 50A to an end voltage of 2.5V; let it stand for 5 minutes; discharge it at a constant current of 10A to an end voltage of 2.5V; during the capacity division process, the equipment automatically measures and records the ambient temperature;

[0076] Step S3, the sum of the capacities of each step of the constant current discharge in step S2 is calculated to be (52.1Ah);

[0077] Step S4, the system retrieves the starting ambient temperature data of the 50A discharge step during the capacity division process, and the system automatically calculates the difference between the actual ambient temperature and the standard ambient temperature of 25°C, and then performs temperature compensation on the battery capacity according to the capacity-temperature relationship coefficient of 0.4%SOC / °C (corresponding to 200mAh / °C in this implementation case);

[0078] Combined with steps S3 and S4, the overall battery capacity compensation formula is: C=C0-(T-25)×a, where C is the battery capacity after compensation, C0 is the sum of the capacities of each step of constant current discharge in step S3, T is the starting ambient temperature of the 1C discharge step in the capacity division process in step S4, and a is the coefficient of the relationship between capacity and temperature in step S3, 50mAh / ℃. According to the above formula, the battery capacity C after compensation in this embodiment is (50.4Ah), and the capacity is 51.5Ah tested according to the standard method in the product specification, which has a large deviation.

[0079] Example 5

[0080] The above contents of the present invention are further described in detail below in conjunction with the accompanying drawings. Figure 1 As shown, taking a 27130150-50Ah lithium iron phosphate lithium-ion battery as an example, a method for improving the accuracy of lithium-ion battery capacity distribution in this embodiment specifically includes the following steps:

[0081] Step S1, before lithium-ion battery capacity division, control the temperature of the capacity division environment to be between 20°C and 35°C;

[0082] Step S2, after the ambient temperature meets the standard requirements, connect the lithium-ion battery to the charging and discharging equipment, charge the lithium-ion battery to 4.2V in a constant current and constant voltage mode of 25A, and the constant voltage end current is 1A; let it stand for 10 minutes after charging; discharge at a constant current of 100A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 15A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 7.5A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 2.5A to an end voltage of 2.5V; let it stand for 5 minutes; discharge at a constant current of 1A to an end voltage of 2.5V; during the capacity division process, the equipment automatically measures and records the ambient temperature;

[0083] Step S3, the sum of the capacities of each step of the constant current discharge in step S2 is (52.88Ah);

[0084] Step S4, the system retrieves the starting ambient temperature data of the 50A discharge step in the capacity division process, and the system automatically calculates the difference between the actual ambient temperature and the standard ambient temperature of 25°C, and then performs temperature compensation on the battery capacity according to the capacity-temperature relationship coefficient of 0.06%SOC / °C (corresponding to 30mAh / °C in this implementation case);

[0085] In step S5, the system automatically compensates the battery capacity according to the pre-set current and capacity relationship 2% SOC (corresponding to 1000 mAh in this implementation case).

[0086] Combined with steps S3, S4, and S5, the overall battery capacity compensation formula is: C=C0-(T-25)×ab, where C is the battery capacity after compensation, C0 is the sum of the capacities of each step of constant current discharge in step S3, T is the starting ambient temperature of the 1C discharge step in the capacity division process in step S4, a is the coefficient of the relationship between capacity and temperature in step S3, 30mAh / ℃, and b is the relationship between current and capacity in step S5, 1000mAh. According to the above formula, the battery capacity C after compensation in this embodiment is (51.64Ah), and the capacity is 51.5Ah tested according to the standard method in the product specification, with a small deviation.

[0087] Comparative Example 5

[0088] Step S1, before lithium-ion battery capacity division, control the temperature of the capacity division environment to be between 20°C and 35°C;

[0089] Step S2, after the ambient temperature meets the standard requirements, connect the lithium-ion battery to the charging and discharging equipment, charge the lithium-ion battery to 4.2V in a 50A constant current and constant voltage mode, and the constant voltage end current is 1A; let it stand for 10 minutes after charging; discharge it at a constant current of 50A to an end voltage of 2.5V; let it stand for 5 minutes; discharge it at a constant current of 10A to an end voltage of 2.5V; during the capacity division process, the equipment automatically measures and records the ambient temperature;

[0090] Step S3, the sum of the capacities of each step of the constant current discharge in step S2 is counted as (51.7Ah);

[0091] Step S4, the system retrieves the starting ambient temperature data of the 50A discharge step during the capacity division process, and the system automatically calculates the difference between the actual ambient temperature and the standard ambient temperature of 25°C, and then performs temperature compensation on the battery capacity according to the capacity-temperature relationship coefficient of 0.4%SOC / °C (corresponding to 200mAh / °C in this implementation case);

[0092] Combined with steps S3 and S4, the overall battery capacity compensation formula is: C=C0-(T-25)×a, where C is the battery capacity after compensation, C0 is the sum of the capacities of each step of constant current discharge in step S3, T is the starting ambient temperature of the 1C discharge step in the capacity division process in step S4, and a is the coefficient of the relationship between capacity and temperature in step S3, 50mAh / ℃. According to the above formula, the battery capacity C after compensation in this embodiment is (50.1Ah), and the capacity is 51.5Ah tested according to the standard method in the product specification, which has a large deviation.

[0093] Example 6

[0094] In this embodiment, three different methods are used to test the battery capacity. The test methods are as follows:

[0095] A Method Customer standard capacity test method (international standard IEC61960). After standard charge, 0.2C constant current discharge to 2.5V capacity. Method B The current production capacity test method adopts the company's internal standard documents. After standard charging, 0.5C+0.2C capacity. Example: 1865-2.0Ah battery capacity standard LP / QW03620.10 G method (method of the present invention) Step S1, before the lithium-ion battery is divided into different capacities, the temperature of the divided capacities environment is controlled at 20-35°C; Step S2, after the temperature meets the standard requirements, the lithium-ion battery is connected to the charging and discharging equipment, and the lithium-ion battery is charged to the specified voltage in a standard constant current and constant voltage mode, and the constant voltage end current is in accordance with the regulations (for example, 0.02C); after charging, it is allowed to stand for 10 minutes; it is discharged at a constant current of 1C to a specified end voltage (for example, 2.5V); it is allowed to stand for 5 minutes; it is discharged at a constant current of 0.4A to a specified end voltage (for example, 2.5V); it is allowed to stand for 5 minutes; it is discharged at a constant current of 0.2A to a specified end voltage (for example, 2.5V); it is allowed to stand for 5 minutes; it is discharged at a constant current of 0.1A to a specified end voltage The device automatically measures and records the ambient temperature during the capacity division process; step S3, the sum of the capacities of each step of the constant current discharge in step S2; step S4, the system calls out the starting ambient temperature data of the 1C discharge step during the capacity division process, the system automatically calculates the difference between the actual ambient temperature and the standard ambient temperature, and then performs temperature compensation on the battery capacity according to the capacity-temperature relationship coefficient (n%SOC / ℃); step S5, the system automatically compensates the battery capacity according to the current-capacity relationship n%SOC set in advance.

[0096] Method A and method G were tested at 24℃-31℃ (1℃ interval each time) to obtain the capacity at different temperatures. Figure 2 Comparing the capacity of method G at different temperatures with the standard capacity of method A, the smaller the capacity difference, the less the capacity is affected by temperature, and the more accurate the capacity recognition is. Figure 2 It can be seen from the results that the battery capacity obtained by the G method has a small deviation from the capacity of the customer's standard method, and the capacity identification is accurate.

Claims

1. A method for improving the accuracy of lithium-ion battery capacity classification, characterized in that: The specific steps are: Step S1, before lithium-ion battery capacity division, control the temperature of the capacity division environment to 20-35°C; Step S2, after the ambient temperature meets the standard requirements, connect the lithium-ion battery to the charging and discharging equipment, and fully charge the lithium-ion battery in a constant current and constant voltage mode of 0.5C-1C, and the constant voltage end current is 0.02-0.05C; after charging, let it stand for 10-20 minutes; Discharge at constant current 1 to the end voltage; let stand for 3-5 minutes; discharge at constant current 2 to the end voltage; let stand for 3-5 minutes; discharge at constant current 3 to the end voltage; let stand for 3-5 minutes; discharge at constant current 4 to the end voltage; let stand for 3-5 minutes; discharge at constant current 5 to the end voltage; during the capacity division process, the equipment automatically measures and records the ambient temperature; the current of current step 1 to current step 5 gradually decreases; The range of current 1 is 0.5-2C, the range of current 2 is 0.2-0.5C, the range of current 3 is 0.1-0.2C, the range of current 4 is 0.05-0.1C, and the range of current 5 is 0.02-0.05C; Step S3, counting the sum of the capacities of each step of the constant current discharge in step S2; Step S4, the battery capacity is subjected to the first temperature compensation, the system calls out the ambient temperature data of the capacity division process, the system automatically calculates the difference between the actual ambient temperature and the standard ambient temperature, and then the battery capacity is subjected to the first temperature compensation according to the relationship coefficient between the capacity and the temperature, and the relationship coefficient between the capacity and the temperature is 0.06%SOC / ℃; Step S5, the second compensation of the battery capacity is performed by the system automatically according to the current and capacity relationship set in advance. This compensation is to compensate for the capacity difference caused by the different discharge currents. The coefficient of the relationship between the capacity and the current is 2% SOC; The overall battery capacity compensation formula is: C=C0-(T-25)×ab, where C is the battery capacity after compensation, C0 is the sum of the capacities of each step of constant current discharge in step S3, T is the starting ambient temperature of the discharge step during the capacity division process in step S4, a is the coefficient of relationship between capacity and temperature in step S4, and b is the coefficient of relationship between capacity and current in step S5.

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