Lithium battery capacity prediction method

Abstract

The invention discloses a lithium battery capacity prediction method. The lithium battery capacity prediction method comprises the following steps: establishing a capacity conversion relation between the charging capacity and the discharging capacity of a battery; testing the to-be-tested battery to obtain the charging capacity of the to-be-tested battery; and predicting the discharge capacity of the to-be-tested battery based on the charge capacity of the to-be-tested battery and the capacity conversion relation. By adopting the scheme, the accuracy of the battery capacity test can be improved, the test process is short in time, the production efficiency can be improved, the energy consumption is reduced, the battery cell manufacturing cost is further reduced, in addition, the establishment of the capacity conversion relation is simple, and the operability is high. The problem that lithium battery capacity prediction is difficult to achieve both accuracy and test time is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a method for predicting the capacity of a lithium battery. Background Art

[0002] Capacity is a key parameter of lithium-ion batteries. The accuracy of capacity testing directly affects the use of batteries. In actual use, lithium-ion batteries connect multiple single lithium batteries in series and parallel to form modules and battery packs. In order to ensure the charging and discharging performance of modules and battery packs, the capacity consistency of single lithium batteries in the group is required to be good. In the conventional production process, the capacity test method first charges the battery to 100% SOC with constant current and constant voltage, and then discharges the battery to the cut-off voltage with constant current. The capacity that can be released during the entire discharge process is the battery capacity. In the subsequent use process, the battery capacity is used as the basis for sorting and grouping to form modules or battery packs. Therefore, the accuracy of capacity testing directly affects the performance of modules or battery packs.

[0003] The conventional capacity test method is to charge the battery at a constant current to the limiting voltage and then at a constant voltage to a charging current of 0.05C under an ambient temperature of 25℃±5℃, let it stand for a period of time, and then discharge the battery at a constant current of 0.2C~1C until the termination voltage. This test method is time-consuming, energy-intensive, and has low production capacity. During high-rate testing, the capacity test is inaccurate due to the temperature rise of the battery. The existing capacity prediction method predicts the full capacity based on the interval capacity. During the entire prediction process, the battery is not charged to 100SOC with constant current and constant voltage. This prediction method causes the internal chemical self-discharge of the battery to be unable to be released, and the self-discharge test cannot screen out abnormal cells, which ultimately leads to poor cell consistency and affects performance. In addition, the existing capacity prediction methods are mainly for ternary batteries, while there are few or no capacity prediction methods for lithium-ion batteries. Summary of the invention

[0004] The present invention provides a lithium battery capacity prediction method to solve the problem that it is difficult to achieve both accuracy and test time in lithium battery capacity prediction.

[0005] According to one aspect of the present invention, a lithium battery capacity prediction method is provided, the lithium battery capacity prediction method comprising:

[0006] Establish the capacity conversion relationship between the charging capacity and the discharging capacity of the battery;

[0007] Testing the battery to be tested to obtain the charging capacity of the battery to be tested;

[0008] The discharge capacity of the battery to be tested is predicted based on the charge capacity of the battery to be tested and the capacity conversion relationship.

[0009] In an optional embodiment of the present invention, the step of establishing a capacity conversion relationship between a charging capacity and a discharging capacity of a battery includes:

[0010] Discharging the battery from a starting SOC to a cut-off voltage of the battery at a first discharge current;

[0011] Charging the battery to 100% SOC with a first charging current to obtain a charging capacity;

[0012] discharging the battery from 100% SOC to the cut-off voltage at a second discharge current to obtain a discharge capacity;

[0013] A capacity conversion relationship is determined based on the charging capacity and the discharging capacity.

[0014] In an optional embodiment of the present invention, the determining of the capacity conversion relationship based on the charging capacity and the discharging capacity includes:

[0015] Get the preset equation;

[0016] The charging capacity and the discharging capacity are fitted based on the preset equation to obtain a capacity conversion relationship.

[0017] In an optional embodiment of the present invention, the preset equation is a preset straight line equation, and the preset straight line equation is C1=A*C0+B, wherein C1 is the discharge capacity, C0 is the charge capacity, and A and B are indefinite constants;

[0018] Accordingly, fitting the charging capacity and the discharging capacity based on the preset equation to obtain a capacity conversion relationship includes:

[0019] Fitting the charge capacity and the discharge capacity based on the preset linear equation to obtain the value of the indeterminate constant;

[0020] Substitute the value of the indeterminate constant into the preset linear equation to obtain a capacity conversion relationship.

[0021] In an optional embodiment of the present invention, charging the battery to 100% SOC with a first charging current to obtain a charging capacity comprises:

[0022] The battery is charged to 100% SOC with a first charging current at a constant current and constant voltage to obtain a charging capacity.

[0023] In an optional embodiment of the present invention, the first discharge current and / or the second discharge current is less than or equal to 0.5C.

[0024] In an optional embodiment of the present invention, the first discharge current and / or the second discharge current is less than or equal to 0.4C.

[0025] In an optional embodiment of the present invention, the first charging current is less than or equal to 0.4C.

[0026] In an optional embodiment of the present invention, the first charging current is less than or equal to 0.33C.

[0027] In an optional embodiment of the present invention, the cut-off voltage is 2.0V or 2.5V.

[0028] The technical solution of the embodiment of the present invention first establishes a capacity conversion relationship between the charging capacity and the discharging capacity of the battery, then tests the battery to be tested to obtain the charging capacity of the battery to be tested, and finally predicts the discharge capacity of the battery to be tested based on the charging capacity of the battery to be tested and the capacity conversion relationship. Therefore, it is only necessary to establish the capacity conversion relationship between the charging capacity and the discharging capacity of the battery in the early stage, and in the later stage, it is only necessary to test and obtain the charging capacity of the battery to be tested, so as to predict the discharge capacity of the battery to be tested, and there is no need to actually test the battery to obtain the discharge capacity of the battery to be tested. This can not only improve the accuracy of the battery capacity test, but also shorten the test process, improve production efficiency, reduce energy consumption and thus reduce the manufacturing cost of the battery cell. In addition, it is relatively simple to establish the capacity conversion relationship and has high operability. It solves the problem that it is difficult to achieve both accuracy and test time in lithium battery capacity prediction.

[0029] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0031] Figure 1 A flow chart of a lithium battery capacity prediction method provided in Embodiment 1 of the present invention;

[0032] Figure 2 A capacity deviation diagram between a discharge capacity of a battery to be tested and an actual discharge capacity of the battery provided in an embodiment of the present invention;

[0033] Figure 3 A flow chart of a lithium battery capacity prediction method provided in Embodiment 2 of the present invention;

[0034] Figure 4 It is a fitting diagram of multiple groups of discharge capacity and charge capacity. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0036] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0037] Embodiment 1

[0038] Figure 1 This is a flow chart of a lithium battery capacity prediction method provided in the first embodiment of the present invention. This embodiment is applicable to the case of performing capacity testing on a lithium battery, such as Figure 1 As shown, the lithium battery capacity prediction method includes:

[0039] S110: Establishing a capacity conversion relationship between the charging capacity and the discharging capacity of the battery.

[0040] Among them, the charging capacity refers to the capacity value of the battery when the battery with initial discharge is charged to the charging termination voltage at the rated charging power. The discharge capacity refers to the capacity value of the battery output measured under specified conditions, and the battery discharge is the process of outputting electrical energy to the outside. The capacity conversion relationship reflects the conversion relationship between the charging capacity and the discharging capacity. In addition, the steps for establishing the capacity conversion relationship between the charging capacity and the discharging capacity of the battery can be established before the battery is manufactured, or after the battery is manufactured, and are not specifically limited here.

[0041] S120, testing the battery to be tested to obtain the charging capacity of the battery to be tested.

[0042] The charging capacity of the battery to be tested is the charging capacity of the battery currently being predicted, and the method for testing the battery to be tested may be a conventional method for testing the charging capacity of a battery, which is not specifically limited herein.

[0043] S130: predicting the discharge capacity of the battery to be tested based on the charge capacity of the battery to be tested and the capacity conversion relationship.

[0044] Among them, the discharge capacity of the battery to be tested is the discharge capacity of the battery currently undergoing capacity prediction. Since the capacity conversion relationship reflects the conversion relationship between the charging capacity and the discharging capacity, the discharge capacity of the battery to be tested can be predicted when the charging capacity of the battery to be tested and the capacity conversion relationship are known.

[0045] also, Figure 2 A capacity deviation diagram of a discharge capacity of a battery to be tested and an actual discharge capacity of a battery provided in an embodiment of the present invention reflects the capacity deviation of the predicted discharge capacity of the battery to be tested and the actual discharge capacity of the battery. The ordinate is the capacity deviation of the discharge capacity of the battery to be tested and the actual discharge capacity of the battery. Figure 2 It can be seen that the capacity deviation between the discharge capacity of the battery to be tested and the actual battery discharge capacity is within ±1.00%, indicating that the capacity deviation between the discharge capacity of the battery to be tested and the actual battery discharge capacity is small, that is, the predicted discharge capacity of the battery to be tested is more accurate.

[0046] The above scheme first establishes the capacity conversion relationship between the charging capacity and the discharging capacity of the battery, then tests the battery to be tested to obtain the charging capacity of the battery to be tested, and finally predicts the discharge capacity of the battery to be tested based on the charging capacity of the battery to be tested and the capacity conversion relationship. Therefore, it is only necessary to establish the capacity conversion relationship between the charging capacity and the discharging capacity of the battery in the early stage, and in the later stage, it is only necessary to test and obtain the charging capacity of the battery to be tested, so as to predict the discharge capacity of the battery to be tested, without actually testing the battery to obtain the discharge capacity of the battery to be tested. It can not only improve the accuracy of the battery capacity test, but also shorten the test process, improve production efficiency, reduce energy consumption and thus reduce the manufacturing cost of the battery cell. In addition, it is relatively simple to establish the capacity conversion relationship and has high operability. It solves the problem that it is difficult to achieve both accuracy and test time in lithium battery capacity prediction.

[0047] Embodiment 2

[0048] Figure 3A flow chart of a lithium battery capacity prediction method provided in Embodiment 2 of the present invention, wherein optionally, the capacity conversion relationship between the charging capacity and the discharging capacity of the battery is established, including: discharging the battery from a starting SOC to a cut-off voltage of the battery with a first discharging current; charging the battery to 100% SOC with a first charging current to obtain a charging capacity; discharging the battery from 100% SOC to the cut-off voltage with a second discharging current to obtain a discharging capacity; and determining a capacity conversion relationship based on the charging capacity and the discharging capacity. The relationship between this embodiment and the above-mentioned embodiments is that Embodiment 1 is an improvement. Figure 3 As shown, the lithium battery capacity prediction method includes:

[0049] S210 , discharging the battery from a starting SOC to a cut-off voltage of the battery at a first discharge current.

[0050] Among them, SOC, the full name of State of Charge, is the charging state of the battery, that is, the remaining power. It indicates the ratio of the remaining dischargeable power to the fully charged power after the battery has been used for a period of time or stored for a long time. The initial SOC is the power of the battery in the initial state, and the first discharge current refers to the current value of the battery during the discharge process. The cut-off voltage refers to the voltage when the battery is fully discharged. Preferably, the cut-off voltage is 2.0V or 2.5V.

[0051] S220 , charging the battery to 100% SOC with a first charging current to obtain a charging capacity.

[0052] Among them, the first charging current refers to the current value when the battery is charged, and 100% SOC means that the battery is fully charged. Since the previous step has discharged the battery to the cut-off voltage of the battery, charging the battery to 100% SOC at this time is to charge the battery from a fully discharged state to a fully charged state, so the charging capacity of the battery can be obtained. Preferably, charging the battery to 100% SOC with the first charging current to obtain the charging capacity includes: charging the battery to 100% SOC with the first charging current at a constant current and constant voltage to obtain the charging capacity. Among them, constant voltage charging has high charging efficiency and less damage to the battery, and can efficiently fully charge the battery without causing damage to the battery.

[0053] S230 , discharging the battery from 100% SOC to the cut-off voltage at a second discharge current to obtain a discharge capacity.

[0054] The second discharge current refers to the current value when the battery is discharged. Since 100% SOC means that the battery is fully charged, discharging the battery from 100% SOC to the cut-off voltage is discharging the battery from a fully charged state to a de-charged state, so the discharge capacity of the battery can be obtained at this time.

[0055] S240: Determine a capacity conversion relationship based on the charging capacity and the discharging capacity.

[0056] Among them, since the capacity conversion relationship reflects the conversion relationship between the charging capacity and the discharging capacity, the capacity conversion relationship can be determined after the charging capacity and the discharging capacity are obtained.

[0057] S250, testing the battery to be tested to obtain the charging capacity of the battery to be tested.

[0058] S260: Predicting the discharge capacity of the battery to be tested based on the charge capacity of the battery to be tested and the capacity conversion relationship.

[0059] Through the above scheme, the capacity conversion relationship between the charging capacity and the discharging capacity can be conveniently and simply determined, and the operability is large. At the same time, the battery is charged with 100% SOC, which can improve the self-discharge screening ability.

[0060] In an optional embodiment of the present invention, the determining of the capacity conversion relationship based on the charging capacity and the discharging capacity includes:

[0061] Get the preset equation.

[0062] The charging capacity and the discharging capacity are fitted based on the preset equation to obtain a capacity conversion relationship.

[0063] Among them, fitting means that several discrete function values ​​{f1, f2, ..., fn} of a certain function are known, and by adjusting several unknown coefficients f (λ1, λ2, ..., λn) in the function, the difference between the function and the known point set (least squares meaning) is minimized. The preset equation is the function that the charging capacity and the discharging capacity will satisfy. The obtained charging capacity and discharging capacity are the known discrete function values, so after knowing the charging capacity and the discharging capacity, the charging capacity and the discharging capacity can be fitted based on the preset equation to obtain the capacity conversion relationship.

[0064] On the basis of the above embodiment, the preset equation is a preset straight line equation, and the preset straight line equation is C1=A*C0+B, wherein C1 is the discharge capacity, C0 is the charge capacity, and A and B are indefinite constants.

[0065] Accordingly, fitting the charging capacity and the discharging capacity based on the preset equation to obtain a capacity conversion relationship includes:

[0066] The charging capacity and the discharging capacity are fitted based on the preset linear equation to obtain a value of the indeterminate constant.

[0067] Substitute the value of the indeterminate constant into the preset linear equation to obtain a capacity conversion relationship.

[0068] The preset linear equation is an equation that the discharge capacity and the charge capacity will satisfy, and the preset linear equation is C1=A*C0+B, where A and B are indefinite constants, that is, A and B are unknown quantities.

[0069] During the test, multiple sets of discharge capacity and charge capacity are usually obtained. At this time, C0 and C1 of the preset linear equation are known quantities, that is, multiple sets of different C0 and C1 can be obtained. At this time, fitting can be performed to obtain the values ​​of the indeterminate constants A and B. After the values ​​of the indeterminate constants A and B are known, the capacity conversion relationship can be obtained by simply substituting them into the preset linear equation.

[0070] Through the above scheme, the capacity conversion relationship can be conveniently determined after the discharge capacity and the charge capacity are obtained.

[0071] The following is a specific example to illustrate a specific method for determining the capacity conversion relationship. Figure 4 is a fitting diagram of multiple groups of discharge capacity and charge capacity; Figure 4 As shown in the figure, after testing, multiple sets of discharge capacity and charge capacity were obtained. At this time, after fitting, A is 0.9206 and B is 7.2223. Therefore, the capacity conversion relationship at this time is C1=0.9206*C0+7.2223. If the subsequent charge capacity of the battery to be tested is 98Ah, the discharge capacity of the battery to be tested is 97.4411.

[0072] In an optional embodiment of the present invention, the first discharge current and / or the second discharge current is less than or equal to 0.5C. When the first discharge current and the second discharge current are too large, the battery may generate heat, and the heating of the battery may cause the measured discharge capacity and charging capacity to be inaccurate. By making the first discharge current and / or the second discharge current less than or equal to 0.5C, the measured discharge capacity and charging capacity can be made more accurate. Preferably, the first discharge current and / or the second discharge current is less than or equal to 0.4C, which can better prevent the battery from generating heat during discharge.

[0073] In an optional embodiment of the present invention, the first charging current is less than or equal to 0.4C. When the first charging current is too large, the battery may generate heat, and the heating of the battery may cause the measured discharge capacity and charging capacity to be inaccurate. By making the first charging current less than or equal to 0.4C, the measured discharge capacity and charging capacity can be made more accurate. Preferably, the first charging current is less than or equal to 0.33C, which can better prevent the battery from heating up during charging.

[0074] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0075] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium battery capacity prediction method, characterized in that: include: Establish the capacity conversion relationship between the charging capacity and the discharging capacity of the battery; Testing the battery to be tested to obtain the charging capacity of the battery to be tested; The discharge capacity of the battery to be tested is predicted based on the charge capacity of the battery to be tested and the capacity conversion relationship.

2. The lithium battery capacity prediction method according to claim 1, characterized in that: The step of establishing a capacity conversion relationship between the charging capacity and the discharging capacity of the battery includes: Discharging the battery from a starting SOC to a cut-off voltage of the battery at a first discharge current; Charging the battery to 100% SOC with a first charging current to obtain a charging capacity; discharging the battery from 100% SOC to the cut-off voltage at a second discharge current to obtain a discharge capacity; A capacity conversion relationship is determined based on the charging capacity and the discharging capacity.

3. The lithium battery capacity prediction method according to claim 2, characterized in that: The determining of the capacity conversion relationship based on the charging capacity and the discharging capacity includes: Get the preset equation; The charging capacity and the discharging capacity are fitted based on the preset equation to obtain a capacity conversion relationship.

4. The lithium battery capacity prediction method according to claim 3, characterized in that: The preset equation is a preset linear equation, and the preset linear equation is C1=A*C0+B, wherein C1 is the discharge capacity, C0 is the charge capacity, and A and B are indefinite constants; Accordingly, fitting the charging capacity and the discharging capacity based on the preset equation to obtain a capacity conversion relationship includes: Fitting the charge capacity and the discharge capacity based on the preset linear equation to obtain the value of the indeterminate constant; Substitute the value of the indeterminate constant into the preset linear equation to obtain a capacity conversion relationship.

5. The lithium battery capacity prediction method according to any one of claims 2 to 4, characterized in that: The step of charging the battery to 100% SOC with a first charging current to obtain a charging capacity comprises: The battery is charged to 100% SOC with a first charging current at a constant current and constant voltage to obtain a charging capacity.

6. The lithium battery capacity prediction method according to any one of claims 2 to 4, characterized in that: The first discharge current and / or the second discharge current is less than or equal to 0.5C.

7. The lithium battery capacity prediction method according to claim 6, characterized in that: The first discharge current and / or the second discharge current is less than or equal to 0.4C.

8. The lithium battery capacity prediction method according to any one of claims 2 to 4, characterized in that: The first charging current is less than or equal to 0.4C.

9. The lithium battery capacity prediction method according to claim 8, characterized in that: The first charging current is less than or equal to 0.33C.

10. The lithium battery capacity prediction method according to any one of claims 2 to 4, characterized in that: The cut-off voltage is 2.0V or 2.5V.

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