CN112363075B - Evaluation method for aging of lithium ion battery - Google Patents
Evaluation method for aging of lithium ion battery Download PDFInfo
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- CN112363075B CN112363075B CN201911149141.9A CN201911149141A CN112363075B CN 112363075 B CN112363075 B CN 112363075B CN 201911149141 A CN201911149141 A CN 201911149141A CN 112363075 B CN112363075 B CN 112363075B
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Abstract
The invention relates to the technical field of lithium ion batteries, and discloses an evaluation method of aging of a lithium ion battery, which comprises the following steps: dividing a plurality of same lithium ion batteries with initial SOC of 100% into two groups, and performing an aging test at the same temperature; the calendar aging test group is placed for N days, the comprehensive aging test group is subjected to periodic charge and discharge, and the circulation working condition of each period is designed according to the actual use condition of the battery and continuously circulates for N days; performing capacity test every M days; calculating capacity attenuation rates delta Q of a calendar aging test group and a comprehensive aging test group respectively Calendar And DeltaQ Total (S) The method comprises the steps of carrying out a first treatment on the surface of the From DeltaQ Total (S) Subtracting DeltaQ Calendar Obtaining the cycle aging capacity attenuation rate delta Q Circulation . The evaluation method can separate calendar aging and cyclic aging for research, and the cyclic aging is more in accordance with the actual cyclic working condition, the analysis result is more practical, and the evaluation method can be used for estimating the service life of the lithium ion battery, researching the aging mechanism and selecting the optimal operation condition.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to an evaluation method for aging of a lithium ion battery.
Background
The lithium ion battery is the most potential energy source for the hybrid electric vehicle and the pure electric vehicle at present, the performance of the lithium ion battery directly influences the performance of the whole vehicle, and the price and the service life of the lithium ion battery are the most important influencing factors for the economical efficiency of the electric vehicle. Although the lithium ion battery can meet the requirements of the electric automobile in terms of power, energy and capacity, the lithium ion battery has obvious advantages compared with other types of batteries in terms of safety and environmental protection. However, the contradiction between the limited service life and the high replacement cost of the lithium ion battery becomes a bottleneck problem of the lithium ion battery technology, and further, the large-scale popularization of the electric automobile is limited. The main causes of aging of lithium ion batteries are loss of positive and negative electrode materials and loss of active lithium. Wherein, the loss of the anode and cathode materials means that the anode and cathode active materials are isolated or dissolved; causes of active lithium loss include the generation of interfacial films (SEI), the consumption of recyclable lithium by thickening, and lithium plating induced when the battery is charged under severe conditions such as high rates or low temperatures. The research on the aging process of the lithium ion battery is beneficial to correctly estimating the service life of the lithium ion battery, selects the best practical operation condition, and is one of important ways for improving the performance of the power lithium ion battery.
The aging of lithium ion batteries mainly comprises two types: cycle aging and calendar aging. Cycle aging refers to aging caused when a battery is charged and discharged, and is determined by measuring a capacity (energy) retention rate during continuous charge and discharge cycles; calendar aging refers to the irreversible capacity loss that occurs during storage of a battery, as determined by measuring the capacity (energy) retention of the battery at a certain state of charge or state of charge (SOC) of the battery at rest. The electric automobile stays in the parking lot for most of the time in actual use, so that the aging of the lithium ion battery is determined by two aging mechanisms. In order to analyze the attenuation of the lithium ion battery more accurately, separate researches on the superimposed calendar aging and cyclic aging are necessary, but the current report generally only carries out independent analysis on one mechanism, cannot meet the actual use requirement of the electric automobile, and has a certain technical limitation. In addition, in the prior art, the lithium ion battery cycle test is to continuously charge and discharge the battery by adopting fixed current in a certain SOC range, but the method is not in line with the actual use condition of the electric automobile, for example, the electric automobile can have a relatively long rest after being charged and discharged for a certain time.
The Chinese patent with the application number of CN201811131200.5 discloses a lithium ion battery life estimation method and a device, which are used for determining the cycle life of the lithium ion battery with a specific failure probability value under the same cycle life experimental working condition; the Chinese patent with the application number of CN201610384214.2 discloses a calendar life test method of a power lithium ion battery, which can be used for analyzing the influence of different rest conditions (charge state, temperature and the like) on the calendar life of the lithium ion battery. Both of these patents only investigate one aging mechanism.
The Chinese patent with the application number of CN201710381912.1 discloses a power battery life prediction method, which comprises the following steps: determining a battery capacity attenuation stage according to the service life attenuation rate of the battery monomer; establishing a capacity decay model of capacity retention rate and chemical reaction rate and time; combining the battery capacity attenuation stage to obtain a cycle life attenuation model and a calendar life attenuation model; training a cycle life attenuation model and a calendar life attenuation model by using the battery monomer measurement data, and determining parameters in the model; generating a cycle life decay curve and a calendar life decay curve according to the cycle life decay model and the calendar life decay model; and superposing the two curves according to a preset proportion to obtain a battery life prediction curve. The cell measurement data includes: the battery monomer is subjected to cycle working condition test after being charged and discharged for N times under different charging and discharging currents, temperatures and discharging depths to obtain test data; and (3) testing data obtained by calendar life test of the battery monomer after standing for M months at different temperatures and under SOC. The battery life prediction method of the invention separately researches calendar aging and cyclic aging, but the cyclic life attenuation condition is data obtained by continuously charging and discharging the battery, which does not accord with the actual service condition of the power battery.
Disclosure of Invention
In order to solve the technical problems, the invention provides an evaluation method for aging of a lithium ion battery. The method realizes the effective separation of calendar aging and cyclic aging, wherein the cyclic aging adopts the cyclic working condition which is more in line with the actual use condition of the battery, so that the analysis result is more practical, and important technical support can be provided for the estimation of the service life of the lithium ion battery, the research of the aging mechanism and the selection of the optimal operation condition.
The specific technical scheme of the invention is as follows:
an evaluation method for aging of a lithium ion battery comprises the following steps:
(1) Dividing a plurality of lithium ion batteries with the same specification and 100% of initial SOC into two groups, wherein the number of the batteries in each group is more than or equal to 2, and respectively performing calendar aging test and comprehensive aging test at the same experimental temperature;
(2) Calendar aging test group: leaving the group of cells for N days, said N being a natural number greater than 0;
(3) Comprehensive aging test group: the battery of the group is charged and discharged periodically, the circulation working condition of each period is designed according to the actual use condition of the lithium ion battery, intermittent charging and discharging are carried out in the same period, and the period is continuously circulated for N days, wherein N is a natural number greater than 0;
(4) And carrying out capacity test on the two groups of batteries at intervals of M days, wherein M is a natural number larger than 0, and the specific process of the capacity test is as follows:
(a) Fully charging and discharging the battery under a constant temperature environment, measuring the electric quantity discharged by the battery, namely the battery capacity, taking an average value after cycling for a plurality of times to obtain the capacity of a single battery, and respectively calculating the average value Q of the battery capacities of each group n Wherein N is the number of days of test, N is more than or equal to 0 and less than or equal to N;
(b) Restoring the SOC of the battery to a state before capacity test;
(5) Calculating the capacity attenuation rate delta Q:
wherein Q is n For the battery capacity measured on day n, Q 0 Is the initial battery capacity; the capacity attenuation rate is calculated for the two groups of batteries respectively, and the capacity attenuation rate of the calendar aging test group is recorded as delta Q Calendar The capacity attenuation rate of the comprehensive aging test group is recorded as delta Q Total (S) ；
(6) Calculating the net cyclic aging capacity attenuation rate delta Q Circulation ：ΔQ Circulation ＝ΔQ Total (S) -ΔQ Calendar 。
The capacity attenuation rate delta Q caused by calendar aging can be obtained by the evaluation method of the invention Calendar Capacity decay rate Δq due to cyclic aging Circulation And an actual total capacity decay rate Δq Total (S) . For most batteries, the capacity fade has obvious law with time, so the service life of the battery can be predicted by analyzing the change relation of calendar aging, cyclic aging and actual total capacity fade with time. By calculating DeltaQ Calendar And DeltaQ Circulation At DeltaQ Total (S) The method can evaluate the influence of calendar aging and cyclic aging on the actual capacity attenuation of the lithium ion battery respectively, and provides important technical support for the research of the aging mechanism of the lithium ion battery. By designing different circulation working conditions and comparing the attenuation conditions of the battery capacity under different circulation working conditions, the influence of different operation conditions (including depth of discharge, charge and discharge current, charge and discharge times and the like) on the attenuation of the battery capacity can be evaluated in the same time, so that the optimal operation condition can be selected, and the service life of the battery can be prolonged.
In the prior art, the battery is continuously charged and discharged to carry out the cyclic aging test, but the cyclic aging rate of the battery is different due to different aging conditions, and the cyclic aging test result is different from the actual cyclic aging test result due to the fact that the cyclic working condition is different from the actual use condition. In actual use, the lithium ion battery of the electric automobile is charged and discharged intermittently, most of the time is in a rest state, and the actual total capacity attenuation is superposition of cyclic aging and calendar aging, so the evaluation method of the invention passes through delta Q Total (S) And DeltaQ Calendar Subtraction to obtain DeltaQ Circulation Wherein DeltaQ Total (S) The test of (1) adopts the circulation working condition which is more in line with the actual use condition of the power battery, so the delta Q obtained by calculation Circulation Will be more practical. In the evaluation method of the present invention, the capacity fade caused by calendar aging during the rest period and during the charge and discharge period is measured as the capacity fade meter at 100% SOC rest, i.e., ΔQ Calendar Since the SOC of the battery is not 100% during the charge and discharge periods and the interval between the charge and discharge periods, Δq is Calendar There is a certain difference from the actual one, but this difference is relative to ΔQ Circulation The error caused is much smaller than in the prior art. In short, the error in the cyclic aging test performed with the prior art results from the effect of aging conditions on the cyclic aging rate, and the present invention eliminates this error, introducing another much smaller error that results from the effect of the SOC on the calendar aging rate.
Preferably, in the step (1), the experimental temperature is 15 to 55 ℃.
Temperature is an important stress affecting capacity fade of lithium ion batteries. The recommended use temperature of the battery is generally 15-35 ℃, and the limit temperature in actual use is 55 ℃; when the experimental temperature is 45-55 ℃, the battery aging can be accelerated due to the reasons of accelerated surface corrosion of the positive electrode material, accelerated consumption of active lithium caused by instability of an interface film (SEI) and the like, and the experimental time is effectively shortened. The battery life at different temperatures has a certain relation, so that the battery life at the actual use temperature can be estimated according to the battery life at a certain experimental temperature.
Preferably, in the step (a), the battery is fully charged and discharged at a rate of 0.3 to 1.2C and a voltage of 2.6 to 4.2V.
Preferably, in the step (a), the number of cycles is 2 to 3.
The experimental error can be reduced by taking the average value through multiple times of circulation, but if the number of times of circulation is too large, the battery can be aged due to the charge and discharge process, and the accuracy of the experimental result can be affected.
Preferably, in the step (b), the SOC of the battery is returned to the state before the capacity test at a rate of 0.3 to 0.5C.
The reason for charging at 0.3-0.5C rate is that high rate charging is easy to cause lithium electroplating and negative electrode material loss, accelerates the increase of internal resistance and the reduction of capacity of the battery, shortens the service life of the battery, so that the charging current for recovering the SOC to a pre-test state after the capacity test is finished cannot be excessive in order to avoid influencing the aging of the battery; and too small a charging current results in too long a charging time.
Preferably, in the step (3), the battery is charged and discharged at a rate of 0.2 to 1.0C.
The charge-discharge current of 0.2-1.0C accords with the actual service condition of the lithium ion battery of the electric automobile.
Preferably, in the step (3), the cycle condition is that the constant voltage and constant current are fully charged once every day at the end of the day, the total discharge is carried out for 2 to 3 times in the day, the first discharge is carried out to 50 to 70 percent of SOC, the second discharge is carried out to 30 to 40 percent of SOC, and the charge-discharge current is 0.2 to 0.5C.
Preferably, in the step (3), the cycle condition is that the constant voltage and constant current are fully charged once every day at the end of the day, the charge is discharged once a day, the charge is discharged to 30-70% of the SOC, and the charge-discharge current is 0.2-0.5 ℃.
Preferably, in the step (3), the cycle condition is that 5-8 times of continuous charging and discharging are performed in one day, the charging and discharging current is 0.8-1.0C, and the charging and discharging are fully charged with constant voltage and constant current at the end of each day.
Preferably, in the step (3), the cycle condition is that the constant voltage and constant current are fully charged once at the end of each week, the total discharge is carried out 5 times in each week, the last discharge reaches 10-30% of the SOC, and the charge-discharge current is 0.2-0.5 ℃.
The four circulation working conditions can better simulate the actual service condition of the battery, so that the circulation aging test result is more practical.
Compared with the prior art, the invention has the following advantages:
(1) The calendar aging and the cyclic aging are effectively separated, and the actual service condition of the lithium ion battery of the electric automobile is met;
(2) The research on the cyclic aging adopts a cyclic working condition which is more in line with reality, so that the analysis result is more in line with reality;
(3) Can provide important technical support for the estimation of the service life of the lithium ion battery, the research of an aging mechanism and the selection of the optimal operation condition.
Drawings
FIG. 1 is a graph showing the cycle aging capacity degradation rate of the batteries of groups # 2 to #5 and comparative examples 1 to 3 according to the cycle number in the examples;
FIG. 2 is a graph of SOC over time for a cycle of the present invention;
FIG. 3 is a graph of SOC over time for a cycle of another cycle of the present invention;
FIG. 4 is a graph of SOC versus time for a cycle of another cycle of the present invention;
FIG. 5 is a graph of SOC versus time for a cycle of another cycle of the present invention;
FIG. 6 is a graph of the battery calendar aged capacity degradation rate of group #1 over shelf time in the example;
fig. 7 is a graph showing the actual total capacity degradation rate of the batteries of groups # 2 to #5 according to the cycle number in the example.
Detailed Description
The invention is further described below with reference to examples.
Examples
An evaluation method for aging of a lithium ion battery comprises the following steps:
(1) 30 lithium ion batteries with the same specification and the initial SOC of 100% are divided into two groups, the number of the batteries of a calendar aging test group (recorded as group # 1) and a comprehensive aging test group is respectively 6 and 24, and aging tests are respectively carried out at 55 ℃.
(2) Calendar aging test group: the batteries of the group were left to rest for 210 days.
(3) Comprehensive aging test group: the battery pack was divided into 4 groups (designated as groups # 2 to #5, respectively) of 6 batteries each. The 4 groups of batteries were periodically charged and discharged according to the 4 cycle conditions shown in fig. 2 to 5, respectively, for 210 days. Wherein, curve 1 in fig. 2 shows that the charging is completely full of electricity at constant voltage and constant current at the end of each day, and the total discharging is carried out 2 times in each day, the first discharging is carried out to 60% of SOC, the second discharging is carried out to 40% of SOC, and the charging and discharging current is 0.3C; curve 2 in fig. 3 shows that the charging is completely full of electricity at constant voltage and constant current at the end of each day, the charging and discharging current is 0.3C once a day, and the difference from fig. 2 is that the discharging depth is smaller, and the discharging is only to 70% soc; curve 3 in fig. 4 shows that 6 continuous charge and discharge are performed in one day, the charge and discharge current is 1.0C, each discharge is to 60% soc, each charge is to 90% soc, and the charge is fully charged with constant voltage and constant current at the end of each day; curve 4 in fig. 5 shows that the charging is completed once at constant voltage and constant current at the end of each week, and the total discharging is performed 5 times in each week, and the last discharging is performed to 30% soc, and the charging and discharging current is 0.3C.
(4) The batteries of groups #1 to #4 were tested for capacity once every 2 days (i.e., day 0, day 2, day 4, … …), and the batteries of group #5 were tested for capacity once every 7 days (i.e., day 0, day 7, day 14, … …), as follows:
(a) At normal temperature, 0.6 times of the temperatureThe battery is fully charged and discharged by the voltage of 3.4V, the electric quantity discharged by the battery, namely the battery capacity, is measured, the average value is obtained after 2 times of circulation, namely the capacity of a single battery, and the average value Q of the battery capacities of each group is calculated respectively n Wherein n is the number of days of test, n is more than or equal to 0 and less than or equal to 210;
(b) The SOC of the battery was restored to the state before the capacity test at a rate of 0.4C.
(5) Calculating the capacity attenuation rate delta Q:
wherein Q is n For the battery capacity measured on day n, Q 0 Is the initial battery capacity. The capacity attenuation rate is calculated for each group of batteries, and the capacity attenuation rate of the calendar aging test group is recorded as delta Q Calendar The capacity attenuation rate of the comprehensive aging test group is recorded as delta Q Total (S) 。
(6) Respectively calculating the net cycle aging capacity attenuation rate delta Q under each cycle working condition Circulation ：ΔQ Circulation ＝ΔQ Total (S) -ΔQ Calendar Wherein DeltaQ Total (S) The capacity attenuation rate of the experimental group under the circulation working condition in the comprehensive aging test group is obtained.
The capacity attenuation rate caused by calendar aging, the capacity attenuation rate caused by cyclic aging and the actual total capacity attenuation rate are respectively delta Q Calendar 、ΔQ Circulation And DeltaQ Total (S) . By the above method, the following conclusions can be drawn:
(1) The change relation of calendar aging, cycle aging and actual total capacity attenuation along with time is shown in fig. 6, 1 and 7 respectively, and on the basis, a battery life attenuation model is established, so that important reference data can be provided for estimating the battery life;
(2) Compared with DeltaQ Calendar In terms of ΔQ Circulation At DeltaQ Total (S) The method has the advantages that the percentage of the lithium ion battery is larger, so that the influence of the cyclic aging on the actual capacity attenuation of the lithium ion battery is larger, and important technical support can be provided for the research on the aging mechanism of the lithium ion battery;
(3) As shown in FIG. 7, the actual total capacity of group # 3 in groups # 2 to #5 is calculated by cycling for the same number of daysAttenuation ratio DeltaQ Total (S) And the minimum, the battery aging is slowest under the second circulation working condition in four circulation working conditions adopted in the experiment, and the service life of the battery can be effectively prolonged by adopting the circulation working conditions.
Comparative example 1
The method for testing the cyclic aging capacity attenuation rate in the prior art comprises the following steps of:
(1) 6 lithium ion batteries with the same specification as that in the embodiment are taken, continuous charge and discharge are carried out at the multiplying power of 0.3C, the discharge is carried out to 40% SOC each time, the charge is carried out to 100% SOC each time, the interval between the charge stage and the discharge stage is only 5min, and each charge and discharge is recorded as one cycle.
(2) The capacity test was performed every 2 cycles (i.e., 0 th, 2 nd, 4 th … …), and the specific procedure was as follows:
(a) Fully charging and discharging the battery at normal temperature with a multiplying power of 0.6C and a voltage of 3.4V, measuring the electric quantity discharged by the battery, namely the battery capacity, taking an average value after 2 times of circulation to obtain the capacity of a single battery, and respectively calculating the average value Q of each group of battery capacities n Wherein n is the number of test cycles;
(b) The SOC of the battery was restored to the state before the capacity test at a rate of 0.4C.
(3) Calculating the cycle aging capacity attenuation rate delta Q Circulation ：
Wherein Q is n Battery capacity measured for the nth cycle, Q 0 Is the initial battery capacity.
Comparative example 2
The method for testing the cyclic aging capacity attenuation rate in the prior art comprises the following steps of:
(1) 6 lithium ion batteries with the same specification as that in the embodiment are taken, continuous charge and discharge are carried out at the multiplying power of 0.3C, each discharge is carried out to 70% SOC, each charge is carried out to 100% SOC, the interval between the charge stage and the discharge stage is only 5min, and each charge and discharge is recorded as one cycle.
(2) The capacity test was performed every 2 cycles (i.e., 0 th, 2 nd, 4 th … …), and the specific procedure was as follows:
(a) Fully charging and discharging the battery at normal temperature with a multiplying power of 0.6C and a voltage of 3.4V, measuring the electric quantity discharged by the battery, namely the battery capacity, taking an average value after 2 times of circulation to obtain the capacity of a single battery, and respectively calculating the average value Q of each group of battery capacities n Wherein n is the number of test cycles;
(b) The SOC of the battery was restored to the state before the capacity test at a rate of 0.4C.
(3) Calculating the cycle aging capacity attenuation rate delta Q Circulation ：
Wherein Q is n Battery capacity measured for the nth cycle, Q 0 Is the initial battery capacity.
Comparative example 3
The method for testing the cyclic aging capacity attenuation rate in the prior art comprises the following steps of:
(1) 6 lithium ion batteries with the same specification as that in the embodiment are taken, continuous charge and discharge are carried out at the multiplying power of 1C, each time the lithium ion batteries are discharged to 60% SOC, each time the lithium ion batteries are charged to 100% SOC, the interval between the charging stage and the discharging stage is only 5min, and each time the lithium ion batteries are charged and discharged is recorded as one cycle.
(2) The capacity test was performed every 2 cycles (i.e., 0 th, 2 nd, 4 th … …), and the specific procedure was as follows:
(a) Fully charging and discharging the battery at normal temperature with a multiplying power of 0.6C and a voltage of 3.4V, measuring the electric quantity discharged by the battery, namely the battery capacity, taking an average value after 2 times of circulation to obtain the capacity of a single battery, and respectively calculating the average value Q of each group of battery capacities n Wherein n is the number of test cycles;
(b) The SOC of the battery was restored to the state before the capacity test at a rate of 0.4C.
(3) Calculating the cycle aging capacity attenuation rate delta Q Circulation ：
Wherein Q is n Battery capacity measured for the nth cycle, Q 0 Is the initial battery capacity.
Comparative example 4
The aging evaluation of the lithium ion battery is carried out according to the following steps:
(1) The number of 18 lithium ion batteries of the same specification, each having an initial SOC of 30%, was divided into two groups, and the number of batteries in the calendar aging test group (designated as group # 6) and the comprehensive aging test group was 6 and 12, respectively, and aging tests were performed at 55 ℃.
(2) Calendar aging test group: the batteries of the group were left to rest for 210 days.
(3) Comprehensive aging test group: the group of cells was divided into 2 groups (designated as group #7 and group #8, respectively) of 6 cells each. The 2 groups of batteries were periodically charged and discharged according to the 2 cycle conditions shown in fig. 2 and 3, respectively, for 210 days. Wherein, curve 1 in fig. 2 shows that the charging is completely full of electricity at constant voltage and constant current at the end of each day, and the total discharging is carried out 2 times in each day, the first discharging is carried out to 60% of SOC, the second discharging is carried out to 40% of SOC, and the charging and discharging current is 0.3C; curve 2 in fig. 3 shows that the charging is completely completed once a day at the end of the day with constant voltage and constant current, and the charging and discharging current is 0.3C once a day, and the difference from fig. 2 is that the depth of discharge is small, and the discharging is only to 70% soc.
(4) The batteries of group #1, group #7, and group #8 were tested for capacity once every 2 days (i.e., day 0, day 2, day 4, … …) as follows:
(a) Fully charging and discharging the battery at normal temperature with a multiplying power of 0.6C and a voltage of 3.4V, measuring the electric quantity discharged by the battery, namely the battery capacity, taking an average value after 2 times of circulation to obtain the capacity of a single battery, and respectively calculating the average value Q of each group of battery capacities n Wherein n is the number of days of test, n is more than or equal to 0 and less than or equal to 210;
(b) The SOC of the battery was restored to the state before the capacity test at a rate of 0.4C.
(5) Calculating the capacity attenuation rate delta Q:
wherein Q is n For the battery capacity measured on day n, Q 0 Is the initial battery capacity. Calculating capacity for each group of batteriesDecay Rate, the capacity decay Rate of the calendar aging test group was recorded as ΔQ Calendar The capacity attenuation rate of the comprehensive aging test group is recorded as delta Q Total (S) 。
(6) Respectively calculating the net cycle aging capacity attenuation rate delta Q under each cycle working condition Circulation ：ΔQ Circulation ＝ΔQ Total (S) -ΔQ Calendar Wherein DeltaQ Total (S) The capacity attenuation rate of the experimental group under the circulation working condition in the comprehensive aging test group is obtained.
TABLE 1
ΔQ measured in comparative examples 1 to 3 Circulation Δq measured after the same number of cycles as groups # 2 to #4 in the examples, respectively Circulation Compare and according to
The deviation between the two is calculated. As can be seen from FIG. 1 and Table 1, the comparative example measured ΔQ after the same number of cycles Circulation Are smaller than the delta Q measured by the corresponding experimental group in the examples Circulation And the deviation was not less than 28%, indicating that the Δq measured by the evaluation method according to the present invention Circulation Delta Q measured in accordance with prior art Circulation There is a large difference between them.
TABLE 2
Further, to verify the effect of the error source of the present invention, SOC affecting calendar aging rate, on the evaluation result, ΔQ measured for group #7 and group #8 in comparative example 4 Circulation Δq measured after the same number of cycles as group # 2 and group # 3 in the example, respectively Circulation Compare and according to
The deviation between the two is calculated.As can be seen from Table 2, the ΔQ measured in comparative example 4 after the same number of cycles Circulation Are all greater than the ΔQ measured in the corresponding experimental group in the examples Circulation But the deviations were less than 6.1%. The experimental result shows that the SOC can influence the calendar aging rate, so that errors are caused to the test of cyclic aging in the evaluation method of the invention, but the SOC has a function of delta Q Circulation Compared with the prior art, the method for testing the cyclic aging provided by the invention has the advantages that the error is small, and the accuracy is obviously improved.
The raw materials and equipment used in the invention are common raw materials and equipment in the field unless specified otherwise; the methods used in the present invention are conventional in the art unless otherwise specified.
The foregoing description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and any simple modification, variation and equivalent transformation of the above embodiment according to the technical substance of the present invention still fall within the scope of the technical solution of the present invention.
Claims (10)
1. The method for evaluating the aging of the lithium ion battery is characterized by comprising the following steps of:
(1) Dividing a plurality of lithium ion batteries with the same specification and 100% of initial SOC into two groups, wherein the number of the batteries in each group is more than or equal to 2, and respectively performing calendar aging test and comprehensive aging test at the same experimental temperature;
(2) Calendar aging test group: leaving the group of cells for N days, said N being a natural number greater than 0;
(3) Comprehensive aging test group: the battery of the group is charged and discharged periodically, the circulation working condition of each period is designed according to the actual use condition of the lithium ion battery, intermittent charging and discharging are carried out in the same period, and the period is continuously circulated for N days, wherein N is a natural number greater than 0;
(4) And carrying out capacity test on the two groups of batteries at intervals of M days, wherein M is a natural number larger than 0, and the specific process of the capacity test is as follows:
(a) Fully charging and discharging the battery in a constant temperature environment, and measuring the electric quantity discharged by the batteryI.e. the battery capacity, taking the average value after cycling for a plurality of times to obtain the capacity of a single battery, and respectively calculating the average value Q of the capacities of each group of batteries n Wherein N is the number of days of test, N is more than or equal to 0 and less than or equal to N;
(b) Restoring the SOC of the battery to a state before capacity test;
(5) Calculating the capacity attenuation rate delta Q:
wherein Q is n For the battery capacity measured on day n, Q 0 Is the initial battery capacity; the capacity attenuation rate is calculated for the two groups of batteries respectively, and the capacity attenuation rate of the calendar aging test group is recorded as delta Q Calendar The capacity attenuation rate of the comprehensive aging test group is recorded as delta Q Total (S) ；
(6) Calculating the net cyclic aging capacity attenuation rate delta Q Circulation ：ΔQ Circulation ＝ΔQ Total (S) -ΔQ Calendar ；
(7) Predicting battery life by analyzing calendar aging, cycle aging, and the change relationship of actual total capacity decay over time; or by calculating DeltaQ Calendar And DeltaQ Circulation At DeltaQ Total (S) The influence of calendar aging and cyclic aging on the actual capacity attenuation of the lithium ion battery is evaluated respectively; or by designing different circulation working conditions, comparing the attenuation conditions of the battery capacity under different circulation working conditions, and evaluating the influence of different operation conditions on the attenuation of the battery capacity in the same time.
2. The method for evaluating aging of a lithium ion battery according to claim 1, wherein in the step (1), the experimental temperature is 15 to 55 ℃.
3. The method of claim 1, wherein in step (a), the battery is fully charged at a rate of 0.3 to 1.2C and a voltage of 2.6 to 4.2V.
4. The method of claim 1, wherein in step (a), the number of cycles is 2 to 3.
5. The method of claim 1, wherein in step (b), the SOC of the battery is returned to a state before the capacity test at a rate of 0.3 to 0.5C.
6. The method for evaluating aging of a lithium ion battery according to claim 1, wherein in the step (3), the battery is charged and discharged at a rate of 0.2 to 1.0C.
7. The method for evaluating aging of a lithium ion battery according to claim 1, wherein in the step (3), the cycle condition is that the battery is fully charged once with constant voltage and constant current at the end of each day, and the battery is discharged for 2 to 3 times in each day, the battery is discharged to 50 to 70% of SOC for the first time, 30 to 40% of SOC for the second time, and the charge-discharge current is 0.2 to 0.5 ℃.
8. The method for evaluating aging of a lithium ion battery according to claim 1, wherein in the step (3), the cycle condition is that the battery is fully charged once with constant voltage and constant current at the end of each day, discharged once a day, discharged to 30-70% soc, and the charge-discharge current is 0.2-0.5 ℃.
9. The method for evaluating aging of a lithium ion battery according to claim 1, wherein in the step (3), the cycle condition is that 5 to 8 times of continuous charge and discharge are performed in a day, the charge and discharge current is 0.8 to 1.0C, and the battery is fully charged with constant voltage and constant current at the end of each day.
10. The method for evaluating aging of a lithium ion battery according to claim 1, wherein in the step (3), the cycle condition is that the battery is fully charged once with constant voltage and constant current at the end of each week, the battery is discharged 5 times in each week, the last time is discharged to 10-30% of the soc, and the charge-discharge current is 0.2-0.5 ℃.
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