CN117538782A - Method for optimizing battery pack terminal electric quantity differential pressure and battery pack - Google Patents
Method for optimizing battery pack terminal electric quantity differential pressure and battery pack Download PDFInfo
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/385—Arrangements for measuring battery or accumulator variables
- G01R31/387—Determining ampere-hour charge capacity or SoC
- G01R31/388—Determining ampere-hour charge capacity or SoC involving voltage measurements
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/385—Arrangements for measuring battery or accumulator variables
- G01R31/387—Determining ampere-hour charge capacity or SoC
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- G—PHYSICS
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- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/389—Measuring internal impedance, internal conductance or related variables
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Abstract
The application belongs to the technical field of battery testing, and particularly relates to an optimization method of battery pack terminal electric quantity differential pressure and a battery pack. According to the optimization method, a plurality of groups of battery cells to be optimized are prepared by taking the factors to be optimized as single variables, the direct current internal resistance of each battery cell to be optimized under different residual electric quantities is tested, the change relation curve of the residual electric quantity and the direct current internal resistance of each battery cell to be optimized is drawn, and the optimal range of the factors to be optimized is determined according to the change relation curve. The optimization method intuitively knows the influence condition of the factors to be optimized on the cell performance by drawing the change relation curve, thereby improving the judgment of the electrochemical performance of the cell system. Determining the optimal range of the factors to be optimized according to the change relation curve; and the battery pack is prepared according to the preferred range of factors to be optimized, so that the direct current impedance (direct current internal resistance) of the discharge end of the battery cell can be minimized while the performance requirement of the battery pack is met, and the consistency of the differential pressure of the end of the battery cell combination (battery pack) is effectively improved.
Description
Technical Field
The application belongs to the technical field of battery testing, and particularly relates to an optimization method of battery pack terminal electric quantity differential pressure and a battery pack.
Background
In order to improve the energy density, the lower limit voltage of the existing metal ion battery (such as a lithium ion battery and a sodium ion battery) is set to be very low, so that more electric quantity can be discharged as much as possible, but for the assembled battery, the consistency among the battery cells is very important, and the voltage of the battery can be rapidly reduced at the discharging end, so that the consistency difference among the battery cells is larger, and the battery pack is easy to lose effectiveness. Therefore, the direct current internal resistance (DCR) of the cells in the battery pack needs to be detected and screened before the battery pack is put into use.
The direct current internal resistance of the battery varies throughout the charge-discharge remaining capacity (SOC) interval due to concentration polarization of metal ion batteries (e.g., lithium ion batteries, sodium ion batteries), and particularly, the variation of DCR is greatest at low SOC. The existing method for detecting the direct current internal resistance of the battery only selects a DCR with a certain charge quantity and compares the DCR with the direct current resistance when a certain SOC (generally 50% SOC) is adopted. The method can not effectively improve the consistency of the differential pressure at the tail ends of the cell combinations.
Disclosure of Invention
The application aims to provide an optimization method of battery pack end electric quantity differential pressure and a battery pack. Aims at solving the technical problem of poor consistency of the voltage difference at the tail end of the battery cell combination.
In order to achieve the purposes of the application, the technical scheme adopted by the application is as follows:
in a first aspect, the present application provides a method for optimizing a battery pack terminal power differential pressure, the method comprising the steps of:
determining a factor to be optimized, and preparing a plurality of groups of battery cores to be tested by taking the factor to be optimized as a single variable;
under the charging or discharging condition, testing the direct current internal resistance of each battery cell to be tested under different residual electric quantity, and drawing a change relation curve of the residual electric quantity and the direct current internal resistance of each battery cell to be tested to obtain a plurality of groups of change relation curves of the battery cells to be tested;
and determining the preferred range of the factors to be optimized according to the change relation curve.
The method for optimizing the battery pack terminal electric quantity differential pressure is provided in the first aspect of the application. Firstly, determining factors to be optimized, and preparing a plurality of groups of battery cells to be tested by taking the factors to be optimized as single variables; under the condition of charging or discharging, testing the direct current internal resistance of each to-be-tested battery cell under different residual electric quantity, and drawing a change relation curve of the residual electric quantity and the direct current internal resistance of each to-be-tested battery cell to obtain a plurality of groups of change relation curves of the to-be-tested battery cells; and determining the preferred range of the factors to be optimized according to the change relation curve. Starting from a battery material system design source, the optimization method obtains the DCR distribution condition of the whole SOC section of the single battery core to be tested by testing the DCR of the whole SOC section of the battery core to be tested and drawing a change relation curve of the direct current internal resistance along with the residual electric quantity; by changing the range of the factors to be optimized and according to the change relation curve of the SOC and the DCR, the influence condition of the factors to be optimized on the performance of the battery cell can be intuitively known, so that the judgment on the electrochemical performance of the battery cell system is improved. Determining the optimal range of the factors to be optimized according to the change relation curve; and then, the battery pack is prepared according to the preferred range of the factors to be optimized, the direct current impedance (direct current internal resistance) of the discharge end of the battery cell can be reduced to the minimum while the performance requirement of the battery pack is met, and the consistency of the differential pressure of the end of the battery cell combination (battery pack) is effectively improved.
As a possible implementation manner of the method for optimizing the battery pack terminal electric quantity differential pressure, before testing the direct-current internal resistance, capacity calibration is performed on each to-be-tested battery cell. In this case, before the dc internal resistance is tested, capacity calibration is performed on each of the cells to be tested, so as to obtain an actual capacity and a service time.
As a possible implementation manner of the method for optimizing the battery pack end power differential pressure of the present application, the method for determining the range of the factors to be optimized includes the steps of: and determining the preferred range of the factors to be optimized according to the cells to be tested, of which the direct current resistance change rate is lower than 60%, in the change relation curves. Under the condition, a group with the lowest direct current internal resistance change rate is selected from more than one group of to-be-tested battery cells with the direct current resistance change rate lower than 60 percent, and is used as a preferred range of the factors to be optimized, and battery cells are prepared by the preferred range, so that the consistency of the terminal differential pressure of a battery cell combination (battery pack) can be effectively improved.
As a possible implementation manner of the method for optimizing the battery pack terminal electric quantity differential pressure, the factor to be optimized is selected from one of the liquid retention amount of the battery cell, the positive electrode material, the negative electrode material, the conductive agent, the binder, the electrolyte and the positive and negative voltage density. The target optimization factors are all factors influencing concentration polarization of the battery cells, and optimization is selected according to actual requirements.
As a possible implementation manner of the method for optimizing the electric quantity differential pressure at the tail end of the battery pack, a charging and discharging test cabinet is adopted to test the direct current internal resistance of each battery cell to be tested, and the times of the direct current internal resistance test of each battery cell to be tested are at least 3. Under the condition, the direct current internal resistance data of at least 3 times are tested, so that a relatively accurate change relation curve of the residual electric quantity and the direct current internal resistance can be drawn, and the optimization effect is ensured.
As a possible implementation manner of the method for optimizing the battery pack end power differential pressure of the present application, the direct current internal resistance test includes the steps of: first, I is 1 Constant-current discharge is carried out for 10 s-20 s, and the test voltage is V 1 In I 2 Discharging for 5 s-10 s, and testing voltage is V 2 The calculation mode of the direct current internal resistance is (V) 2 -V 1 )/(I 2 -I 1 )。
As a possible implementation manner of the method for optimizing the voltage difference of the electric quantity at the tail end of the battery pack, when testing the direct-current internal resistance under different residual electric quantities, each to-be-tested battery cell is subjected to equal gradient change or unequal gradient change between the different residual electric quantities.
Further, the step of testing the internal DC resistance of the battery cell to be tested by adopting the equal gradient change comprises the following steps: testing the direct current internal resistance every time the electric quantity of N% is reduced or increased; wherein N is E (0, 100). In this case, the isocratic variation is easy to handle for recording during the test.
Further, the step of testing the internal DC resistance of the battery cell to be tested by adopting the equal gradient change comprises the following steps: and testing the direct current internal resistance of the battery cell to be tested once every 10% of electric quantity is reduced or increased. Under the condition, more than one group of to-be-tested battery cores with the 20% residual electric quantity and the 10% residual electric quantity of the battery cores and the direct current internal resistance change rate lower than 60% are selected from a plurality of groups of change curves, and then the group with the lowest direct current internal resistance change rate is selected as the preferred range of the to-be-optimized factors.
Further, the testing the direct current internal resistance of the battery cell to be tested by adopting the unequal gradient change comprises: in this case, the non-uniform gradient change can select more residual electric quantity points to test the DC internal resistance in the test process, and the drawn change curve can be more accurate.
As a possible implementation manner of the method for optimizing the battery pack terminal electric quantity differential pressure, the battery cell to be tested comprises at least one of a lithium ion battery cell and a sodium ion battery cell. Under the condition, the lithium ion battery core and the sodium ion battery core are secondary batteries, and the battery core can be repeatedly tested during optimization, so that errors are avoided; in addition, the voltage difference of the electric quantity at the tail end of the battery pack formed by the lithium ion battery cell or the sodium ion battery cell is large, so that the charge and discharge performance of the battery pack is influenced, the battery pack is easy to lose efficacy, and the consistency of the voltage difference at the tail end of the optimized battery pack is obviously improved.
In a second aspect, the present application provides a battery pack prepared after obtaining a preferred range of factors to be optimized according to the optimization method described in the first aspect of the present application.
The battery pack provided in the second aspect of the application is prepared after optimization. The change rate of the direct current internal resistance in the change relation curve of all the battery cells in the battery pack is lower than 60%, so that the consistency of the voltage difference at the tail end of the battery pack is high.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following description will briefly introduce the drawings that are needed in the embodiments or the description of the prior art, it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic flow chart of an optimization method for the battery pack end power differential pressure in the embodiment of the application;
fig. 2 is a schematic diagram of a change relationship between a residual electric quantity and a direct current internal resistance at normal temperature in an embodiment of the present application;
fig. 3 is a schematic diagram of a change relationship between the residual electric quantity and the dc internal resistance at a low temperature of 0 ℃ in the embodiment of the application.
Detailed Description
In order to make the technical problems, technical schemes and beneficial effects to be solved by the present application more clear, the present application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application.
In this application, the term "and/or" describes an association relationship of an association object, which means that there may be three relationships, for example, a and/or B may mean: a alone, a and B together, and B alone. Wherein A, B may be singular or plural. The character "/" generally indicates that the context-dependent object is an "or" relationship.
In the present application, "at least one" means one or more, and "a plurality" means two or more. "at least one of" or the like means any combination of these items, including any combination of single item(s) or plural items(s). For example, "at least one (individual) of a, b, or c," or "at least one (individual) of a, b, and c," may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, c may be single or multiple, respectively.
It should be understood that, in various embodiments of the present application, the sequence number of each process does not mean that the sequence of execution is sequential, and some or all of the steps may be executed in parallel or sequentially, where the execution sequence of each process should be determined by its functions and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.
The terminology used in the embodiments of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
The weights of the relevant components mentioned in the embodiments of the present application may refer not only to specific contents of the components, but also to the proportional relationship between the weights of the components, and thus, any ratio of the contents of the relevant components according to the embodiments of the present application may be enlarged or reduced within the scope disclosed in the embodiments of the present application. Specifically, the mass described in the specification of the examples of the present application may be a mass unit known in the chemical industry such as μ g, mg, g, kg.
The terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated for distinguishing between objects such as substances from each other. For example, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX, without departing from the scope of embodiments of the present application. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature.
The term "PVDF" refers to polyvinylidene fluoride.
The term "CNT" refers to carbon nanotubes.
The term "Super-p" refers to small particle conductive carbon black.
The term "SOC" refers to the state of charge, also called the remaining charge, and represents the remaining capacity of a battery after a period of use or long-term rest.
The term "SOH" refers to the capacity, health and performance state of a battery, and simply refers to the ratio of the performance parameter to the nominal parameter of the battery after a period of use, wherein the newly shipped battery is 100% and the total rejection is 0%. SOH is the ratio of the capacity discharged from the battery discharged to the cutoff voltage at a constant rate from the full charge state to the nominal capacity corresponding to the discharge capacity, and is simply understood as the limit capacity of the battery. The internal resistance of the battery has a certain relation with SOH. The lower the SOH, the larger the internal resistance of the lithium ion battery, the internal resistance value of the battery is indirectly calculated by detecting data such as voltage, current, temperature and the like, and then the SOH is calculated according to the relation between the SOH and the internal resistance of the battery. However, the internal resistance of the battery is not obvious when the SOH variation range is not large, and when the battery is seriously aged, the resistance value is greatly changed, so that the method has larger measurement error when the SOH variation is smaller.
The term "DCR" refers to the internal dc resistance. In the process of charging and discharging the battery, the electron and the ion are hindered by the direct current internal resistance DCR, and the direct current internal resistance DCR is divided into ohmic internal resistance, electrochemical reaction internal resistance and diffusion internal resistance. The lithium battery DCR test aims to evaluate the consistency of the internal resistance of the battery, the impedance value of the welding or connecting end of the module, and the capability of evaluating the discharge power or energy.
The term "N ε (0, 100)" means that N has a value between 0 and 100, but does not take on values of 0 and 100.
The term "(0%, 100% ]" is a range of 0% to 100% of the charge, 100% of the charge being possible but not 0%.
An embodiment of the present application provides a method for optimizing a battery pack terminal power differential pressure, as shown in fig. 1, where the optimizing method includes the following steps:
s10, determining a factor to be optimized, and preparing a plurality of groups of battery cells to be tested by taking the factor to be optimized as a single variable.
S20, under the condition of charging or discharging, testing the direct current internal resistance of each battery cell to be tested under different residual electric quantities, and drawing a change relation curve of the residual electric quantity and the direct current internal resistance of each battery cell to be tested to obtain a plurality of groups of change relation curves of the battery cells to be tested.
S30, determining the preferred range of the factors to be optimized according to the change relation curve.
The method for optimizing the battery pack terminal electric quantity differential pressure is provided in the first aspect of the embodiment of the application. Firstly, determining factors to be optimized, and preparing a plurality of groups of battery cells to be tested by taking the range of the factors to be optimized as a single variable; under the condition of charging or discharging, testing the direct current internal resistance of each battery cell to be tested under different residual electric quantity, and drawing a change relation curve of the residual electric quantity and the direct current internal resistance of each battery cell to be tested to obtain a plurality of groups of change relation curves of the battery cells to be tested; and determining the range of the factors to be optimized after optimization according to the change relation curve. The optimization method starts from a battery material system design source, and obtains the DCR distribution condition of the single full SOC section of the battery cell to be tested by testing the DCR of the full SOC section of the battery cell to be tested and drawing a change relation curve of the direct current internal resistance along with the residual electric quantity; by changing the range of the factors to be optimized and according to the change relation curve of the SOC and the DCR, the influence condition of the factors to be optimized on the performance of the battery cell can be intuitively known, so that the judgment on the electrochemical performance of the battery cell system is improved. Determining the optimal range of the factors to be optimized according to the change relation curve; and the battery pack is prepared according to the preferred range of factors to be optimized, so that the direct current impedance (direct current internal resistance) of the discharge end of the battery cell can be minimized while the performance requirement of the battery pack is met, and the consistency of the differential pressure of the end of the battery cell combination (battery pack) is effectively improved.
As a possible implementation manner of the method for optimizing the battery pack terminal power differential pressure in the embodiment of the present application, in the step S10, the factors to be optimized are selected from the amount of the battery cell retention, the positive electrode material, the negative electrode material, the conductive agent, the binder, the electrolyte, the positive and negative voltage density, or other factors affecting the battery concentration polarization.
As a possible implementation manner of the method for optimizing the battery pack terminal power differential pressure in the embodiment of the present application, in the step S10, the battery cell to be tested includes at least one of a lithium ion battery cell and a sodium ion battery cell. Under the condition, the lithium ion battery core and the sodium ion battery core are secondary batteries, and the battery core can be repeatedly tested during optimization, so that errors are avoided; in addition, the voltage difference of the electric quantity at the tail end of the battery pack formed by the lithium ion battery cell or the sodium ion battery cell is large, so that the charge and discharge performance of the battery pack is influenced, the battery pack is easy to lose efficacy, and the consistency of the voltage difference at the tail end of the optimized battery pack is obviously improved.
As a possible implementation manner of the method for optimizing the battery pack terminal power differential pressure in the embodiment of the present application, in the step S10, the preparation of the to-be-measured battery cell includes the steps of:
obtaining a positive electrode material, a binder, a conductive agent and a negative electrode material comprising a cell to be tested, and respectively preparing into slurry under a vacuum condition;
respectively coating the sizing agents of the positive electrode material and the negative electrode material on a metal foil to obtain a positive electrode plate and a negative electrode plate, and respectively carrying out roller pair, slitting and assembly on the positive electrode plate and the negative electrode plate and then drying to obtain a semi-finished product of the battery cell;
and (5) injecting liquid, forming and separating the semi-finished product of the battery cell to obtain the battery cell to be tested.
In this case, several groups of cells to be tested are prepared with only the factor to be optimized as a single variable.
In some embodiments, the positive electrode material comprises at least one of a nickel cobalt manganese ternary positive electrode material, a nickel cobalt aluminum ternary positive electrode material, lithium iron phosphate, lithium cobaltate, lithium manganate, ferric ferrocyanide (Prussian blue), sodium iron phosphate, sodium vanadium phosphate. In this case, nickel cobalt manganese ternary positive electrode material, nickel cobalt aluminum ternary positive electrode material, lithium iron phosphate, lithium cobaltate and lithium manganate are used as lithium battery positive electrode materials, and iron ferrocyanide (Prussian blue), sodium iron phosphate and sodium vanadium phosphate belong to layered oxides and are used as sodium ion battery positive electrode materials.
In some embodiments, the binder comprises polyvinylidene fluoride (PVDF).
In some embodiments, the conductive agent includes one of Carbon Nanotubes (CNT), small particle conductive carbon black (Super-p), graphene.
In some embodiments, the negative electrode material comprises at least one of graphite, silicon oxygen, silicon carbon, hard carbon. Graphite, silicon oxygen and silicon carbon are used as negative electrode materials of lithium batteries, and hard carbon is used as a negative electrode material of sodium ion batteries.
In some embodiments, the step of coating the slurries of the positive electrode material and the negative electrode material on the metal foil respectively includes: the coating is carried out in an environment of less than 10% humidity using a transfer or extrusion coater. In this case, the anode and cathode sheets obtained by coating are stable in properties and uniform in layout.
In some embodiments, the dried positive electrode sheet has a thickness of 50 μm to 200 μm. The thickness of the positive electrode sheet may be, for example, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, or the like.
In some embodiments, the dried negative electrode sheet has a thickness of 50 μm to 150 μm. The thickness of the negative electrode sheet may be, for example, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, or the like.
In some embodiments, the metal foil comprises at least one of aluminum foil, copper foil, gold foil, silver foil. The metal foils have good conductivity and lower resistance, and errors occurring in detecting the direct current internal resistance of the battery cell to be detected are reduced.
In some embodiments, the step of pairing the rollers comprises: and respectively carrying out roller pair and rolling on the positive pole piece and the negative pole piece according to the thickness of the target electrode.
In some embodiments, the slitting step comprises: and cutting the positive pole piece and the negative pole piece after the pair roller by adopting a full-automatic cutting machine according to the target width.
In some embodiments, the assembling step comprises: and welding and assembling the cut positive electrode plate and the cut negative electrode plate by adopting semi-automatic or full-automatic assembling equipment to obtain the electrode core plate.
In some embodiments, the step of drying comprises: and drying the electrode plate at the temperature of 80-120 ℃ until the moisture of the electrode plate is lower than 300ppm.
In some embodiments, the steps of injecting, forming and partitioning the cell semi-finished product include:
obtaining electrolyte of an electric core;
injecting electrolyte into the semi-finished product of the battery cell, vacuumizing and sealing, and standing for more than 3 days;
and adopting a high-precision battery test system to perform formation and capacity division on the semi-finished product of the battery core.
In some embodiments, the electrolyte includes a high purity organic solvent and an electrolyte lithium/sodium salt.
As a possible implementation manner of the method for optimizing the battery pack terminal power differential pressure in the embodiment of the present application, in step S10, each group of to-be-measured cells is more than 3. In this case, setting 3 or more cells to be tested per group reduces errors due to the small number of cells to be tested.
As a possible implementation manner of the method for optimizing the battery pack terminal power differential pressure in the embodiment of the present application, in the step S20, before testing the dc internal resistance, capacity calibration is performed on each to-be-tested battery cell. Under the condition, before testing the DC internal resistance, the capacity calibration is carried out on each cell to be tested so as to obtain the actual capacity and the service time.
As a possible implementation manner of the method for optimizing the battery pack terminal power differential pressure in the embodiment of the present application, in the step S20, a charging and discharging test cabinet is used to perform a dc internal resistance test on each to-be-tested battery cell, where the number of times of the dc internal resistance test of each to-be-tested battery cell is at least 3. In this case, the direct current internal resistance data of at least 3 times can draw a relatively accurate change relation curve of the residual electric quantity and the direct current internal resistance, so as to ensure the optimization effect.
As a possible implementation manner of the method for optimizing the battery pack end power differential pressure in the embodiment of the present application, in the step S20, the dc internal resistance test includes the steps of: first, I is 1 (e.g. 0.1-1.0C) constant current discharge for 10 s-20 s, test voltage is V 1 In I 2 (e.g. 1C-10C) discharge for 5 s-10 s, test voltage is V 2 The DC internal resistance is calculated by (V) 2 -V 1 )/(I 2 -I 1 )。
As a possible implementation manner of the method for optimizing the battery pack terminal power differential pressure in the embodiment of the present application, in the step S20, when testing the dc internal resistance under different residual power for each battery cell to be tested, the residual power is changed in an equal gradient or in a non-equal gradient.
In some embodiments, the step of testing the internal dc resistance of the cell under test using an isocratic change comprises the steps of: testing the direct current internal resistance once every N% of electric quantity is reduced/increased; wherein N is E (0, 100).
In some embodiments, the step of testing the internal dc resistance of the cell to be tested using an isocratic change includes the steps of: and testing the direct current internal resistance of the battery cell to be tested once every 10% of electric quantity is reduced or increased. Under the condition, more than one group of to-be-tested battery cores with the 20% residual electric quantity and the 10% residual electric quantity of the battery cores and the direct current internal resistance change rate lower than 60% are selected from a plurality of groups of change curves, and then the group with the lowest direct current internal resistance change rate is selected as the preferred range of the to-be-optimized factors.
In some embodiments, testing the internal dc resistance of the cell under test using non-uniform gradient variation includes: and randomly selecting different residual electric quantities from the electric quantity range of (0%, 100% ], and testing the direct current internal resistance.
As a possible implementation manner of the method for optimizing the battery pack end power differential pressure in the embodiment of the present application, in the step S30, a manner of determining the range of factors to be optimized after optimization includes the steps of: and determining the preferred range of the factors to be optimized according to the cells to be tested, of which the direct-current resistance change rate is lower than 60%, in the change relation curves of the groups. Under the condition, a group with the lowest change rate is selected from the to-be-tested battery cells with the direct-current resistance change rate lower than 60%, and battery cells are prepared by adopting the corresponding range of the to-be-optimized factors, so that the consistency of the terminal differential pressure of the battery cell combination (battery pack) can be effectively improved.
A second aspect of the embodiments of the present application provides a battery pack, where the battery pack is prepared after the battery pack obtains the range of factors to be optimized according to the optimization method of the first aspect of the embodiments of the present application.
The battery pack provided in the second aspect of the embodiment of the present application is prepared after optimization. The change rate of the direct current internal resistance in the change relation curves of all the battery cells in the battery pack is lower than 60%, so that the consistency of the voltage difference at the tail ends of the battery cell combinations is high.
As one possible implementation of the battery pack in the embodiments of the present application, the battery pack is a lithium ion secondary battery pack or a sodium ion secondary battery pack. In this case, the retention rate of the electric capacity after 400 cycles to the battery pack is in the range of 80% to 95%.
The following description is made with reference to specific embodiments.
Example 1
The optimizing method of the battery pack terminal electric quantity differential pressure comprises the following steps:
(1) The selected target optimization factors are negative electrode compaction, the ranges of the negative electrode compaction are 1.5 compaction, 1.6 compaction and 1.7 compaction, and the number of the battery cells to be tested for each group of positive and negative electrode compaction is determined to be 3.
(2) Preparing to-be-tested battery cores of 1.5 compaction groups, 1.6 compaction groups and 1.7 compaction groups respectively, wherein the positive electrode materials, the binder, the electrolyte, the conductive agent and the negative electrode materials of all the battery cores are the same during preparation, the surface density and the compaction density of positive electrode plates are the same, and the thickness of negative electrode plates corresponds to 1.5g/cm of different negative electrode compaction densities 3 (1.5 compaction), 1.6g/cm 3 (1.6 compaction), 1.7g/cm 3 (1.7 compaction).
(3) Capacity calibration was performed for the three groups 1.5 compaction group, 1.6 compaction group and 1.7 compaction group, respectively.
(4) And sequentially carrying out direct current internal resistance test on the battery cells in the compaction group 1.5: under normal temperature and normal pressure, the battery core is fully charged, and then DCR is tested once every 10% of SOC from the full charge, DCR1 is tested once every 100% of SOC, DCR2 is tested once every 90% of SOC, DCR3 is tested once every 80% of SOC, and the cycle is performed until DCR10 is tested once at 10% of SOC; likewise, the same dc internal resistance test was performed on the cells of the 1.6 compacted group and the 1.7 compacted group, respectively. Drawing a change relation curve of the residual electric quantity and the direct current internal resistance of each battery cell to be tested to obtain a change relation curve of 3 groups of battery cells to be tested; and selecting more than one group of to-be-tested battery cores with the direct current internal resistance change rate of 20% of the battery cores and 10% of the residual electric quantity lower than 60% from the three groups of change curves, and selecting the group with the lowest direct current internal resistance change rate as the preferred range of the to-be-optimized factors.
The DCR test mode is that 0.1C constant current is firstly discharged for 10s, and the test voltage is V 1 Discharging for 5s at 1C, and measuring voltage to be V 2 ，DCR＝(V 2 -V 1 ) /(1C-0.1C). The obtained direct current internal resistance test data are shown in the following table 1, and the change relation curve is shown in fig. 2.
TABLE 1
From table 1 and fig. 2, it can be seen that by comparing the DCR of each different SOC segment of the cell for the three schemes of the 1.5 compaction group, the 1.6 compaction group and the 1.7 compaction group, the DCR at 10% SOC is generally much higher than the DCR values of the other SOC segments, resulting in an instantaneous increase in the voltage differential at 10% SOC at the discharge end of the cell. The overall SOC distribution for the three schemes was relatively stable, but the 1.7 compaction scheme was overall larger.
The DCR of the three groups of battery cells to be tested is greatly increased at the 10% SOC of the tail end, and the difference delta DCR between the 10% SOC stage and the 20% SOC stage is compared, so that the delta DCR at 1.7 voltage is the maximum in average value and the DCR change rate is the maximum. 1.5 compaction and 1.6 compaction schedule Δdcr is minimal and DCR rate of change is minimal. Since the voltage difference Δv=current I of the battery pack is the dc internal resistance DCR, the terminal voltage difference Δv of a group of cells formed by the scheme becomes large when compacting 1.7, and the difference between the same group of cells is amplified.
In summary, the 1.6 compaction scheme Δdcr of the cells to be tested obtained according to the optimization method of embodiment 1 is the smallest, the DCR change rate is the smallest, and the scheme is selected as a group of cells obtained after optimization.
Example 2
The method for optimizing the battery pack terminal power differential pressure in embodiment 2 is basically the same as that in embodiment 1, except that:
the battery core is fully charged at normal temperature, the constant volume is carried out after the battery core is placed at 0 ℃ for 2H, the battery core is fully charged after the battery core is recovered to the normal temperature, and the DC internal resistance test is carried out after the battery core is placed at 0 ℃ for 2H.
The obtained direct current internal resistance test data are shown in the following table 2, and the change relation curve of the residual electric quantity and the direct current internal resistance is shown in the attached figure 3.
TABLE 2
As can be seen from table 2 and fig. 3, the change rule of the direct current internal resistance was similar to that of the example 1 at normal temperature at 0 ℃. However, at 0 ℃, the difference in DCR at terminal SOC is significantly amplified, which further indicates that the effect of concentration polarization is dominant at low temperatures, thus allowing the terminal charge DCR to be abnormally increased at low temperatures.
Comparative example 1
The method for optimizing the battery pack terminal power differential pressure provided in comparative example 1 is basically the same as that in example 1, except that:
only 50% of the residual electric quantity is selected for direct current internal resistance detection. The detection results are shown in table 3 below.
TABLE 3 Table 3
As can be seen from table 3, when only 50% of the remaining power is selected for direct current internal resistance detection, the difference of detection results is small, the relevant characteristics of terminal pressure difference are not reflected, the direct current internal resistances of the three groups of compaction schemes at 50% of the remaining power are not much different, and the 1.7 compaction scheme DCR is the smallest as the average value is obtained.
To verify the progress of the examples of the present application, the schemes of the cells of examples 1 to 2 and comparative example 1 were prepared according to the same assembly method (v=2mv, r=1mΩ, cap=20mah, k=0.02 mv/h) to make the number of required cells into a 4S8P battery pack, and normal temperature cycle test was performed, charging to 16.8V and discharging to 11V under the condition of 1C (16A) charging and 1C (16A) discharging, and resting for 30min for each charge and discharge period, and normal temperature cycle test was performed 400 times according to the mode. The capacity retention of the cycle is shown in table 4 below.
TABLE 4 Table 4
As can be seen from Table 4 above, the initial pressure difference of the 1.7 compacted battery pack of examples 1 and 2 was greater than that of the 1.6 compacted battery pack after the cyclic test, the end pressure difference of the 1.7 compacted battery pack was gradually increased after 400 cycles, the capacity retention rate was also rapidly decreased, the capacity retention rate was 86% after 400 cycles, and the end pressure difference of the 1.6 compacted battery pack was initially smaller, but the rising trend was smaller and the capacity retention rate was 93.6% after 400 cycles.
While the cycle trends of comparative example 1 were also 1.5 and 1.6, the die set end differential pressure was small, and 1.7 compaction was the preferred option for comparative example 1, with the minimum cycle capacity retention after 400 cycles and the maximum die set end differential pressure. From this, it is understood that the dc resistance DCR at a certain SOC (typically 50% SOC) is compared with the DCR at a certain charge amount only selected in comparative example 1. The method can not effectively improve the consistency of the differential pressure at the tail ends of the cell combinations.
The foregoing description of the preferred embodiments of the present application is not intended to be limiting, but is intended to cover any and all modifications, equivalents, and alternatives falling within the spirit and principles of the present application.
Claims (10)
1. An optimization method of battery pack terminal electric quantity differential pressure is characterized by comprising the following steps:
determining a factor to be optimized, and preparing a plurality of groups of battery cores to be tested by taking the factor to be optimized as a single variable;
under the charging or discharging condition, testing the direct current internal resistance of each battery cell to be tested under different residual electric quantity, and drawing a change relation curve of the residual electric quantity and the direct current internal resistance of each battery cell to be tested to obtain a plurality of groups of change relation curves of the battery cells to be tested;
and determining the preferred range of the factors to be optimized according to the change relation curve.
2. The method for optimizing the battery pack terminal power differential pressure according to claim 1, wherein before the direct current internal resistance is tested, capacity calibration is performed on each cell to be tested;
and/or the method for determining the range of the factors to be optimized comprises the following steps: and determining the preferred range of the factors to be optimized according to the cells to be tested, of which the direct current resistance change rate is lower than 60%, in the change relation curves.
3. The method for optimizing the battery pack terminal power differential pressure according to claim 1, wherein the factor to be optimized is selected from one of a liquid retention amount of a battery cell, a positive electrode material, a negative electrode material, a conductive agent, a binder, an electrolyte, and a positive and negative voltage solid density.
4. The method for optimizing the battery pack terminal power differential pressure according to any one of claims 1 to 3, wherein a charging and discharging test cabinet is adopted to perform direct current internal resistance test on each cell to be tested, and the number of direct current internal resistance tests of each cell to be tested is at least 3.
5. The method for optimizing the battery pack end power differential pressure according to claim 4, wherein the direct current internal resistance test comprises the steps of: first, I is 1 Constant-current discharge is carried out for 10 s-20 s, and the test voltage is V 1 In I 2 Discharging for 5 s-10 s, and testing voltage is V 2 The calculation mode of the direct current internal resistance is (V) 2 -V 1 )/(I 2 -I 1 )；
And/or, for each to-be-tested battery cell, when testing the direct current internal resistance under different residual electric quantities, the different residual electric quantities are in equal gradient change or non-equal gradient change.
6. The method for optimizing the voltage difference of the electric quantity at the tail end of the battery pack according to claim 5, wherein the step of testing the direct current internal resistance of the battery cell to be tested by adopting the equal gradient change comprises the following steps: testing the direct current internal resistance of the battery cell to be tested once every time the electric quantity of N% is reduced or increased; wherein N is E (0, 100).
7. The method for optimizing the voltage difference of the electric quantity at the tail end of the battery pack according to claim 6, wherein the step of testing the direct current internal resistance of the battery cell to be tested by adopting the equal gradient change comprises the following steps: and testing the direct current internal resistance of the battery cell to be tested once every 10% of electric quantity is reduced or increased.
8. The method of optimizing a battery pack terminal power differential pressure according to claim 5, wherein testing the dc internal resistance of the battery cell to be tested using the unequal gradient variation comprises: and randomly selecting different residual electric quantities from the electric quantity range of (0%, 100% ], and testing the direct current internal resistance.
9. The method for optimizing a battery pack terminal power differential pressure according to any one of claims 1-3 or 5-8, wherein the battery cell to be tested comprises at least one of a lithium ion battery cell and a sodium ion battery cell.
10. A battery pack, characterized in that the battery pack is prepared after the battery pack has obtained a preferred range of factors to be optimized according to the optimization method as claimed in any one of claims 1 to 9.
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