Battery operating condition energy efficiency evaluation method

Abstract

The present application relates to the technical field of power battery energy testing, and discloses a battery working condition energy efficiency evaluation method, comprising the following steps: standing the battery cell; charging to full electricity cut-off voltage B with a current I1, and then charging with constant voltage until the current decreases to I2, determining that the battery cell is fully charged, and stopping charging; standing the battery cell; charging to empty electricity cut-off voltage C with a current I3; standing the battery cell; charging to full electricity cut-off voltage B with a constant power P1, and obtaining the energy E1 of a single battery cell; standing the battery cell; setting a test working condition, discharging the battery cell to empty electricity cut-off voltage C under the test working condition, and obtaining the net discharge energy E2 of a single battery cell; and calculating the energy efficiency P3 of the battery cell under the test working condition. The present application can simplify the test process, reduce the test time and economic cost, improve the research and development efficiency and product iteration speed by performing energy efficiency testing at the battery cell level without assembling the battery cell into a module, packing and placing the battery cell in a whole vehicle or a large energy storage cabinet.

Description

Technical Field

[0001] This invention relates to the field of power battery energy testing technology, specifically to a method for evaluating battery operating condition energy efficiency. Background Technology

[0002] With the rapid development of new energy vehicles and energy storage systems, batteries, as key energy storage components, directly impact the operating efficiency and economy of the entire vehicle or system. Battery energy efficiency is a crucial indicator for measuring energy loss during charging and discharging. Accurately assessing battery energy efficiency under real-world operating conditions is essential for improving the overall energy efficiency of battery systems, optimizing battery management strategies, and reducing operating costs. Particularly in the new energy vehicle sector, improving battery energy efficiency can effectively extend driving range and increase user acceptance of electric vehicles.

[0003] Currently, the industry generally adopts the method of integrating the complete battery pack or even the entire vehicle into a large energy storage cabinet or test platform to simulate operating parameters such as temperature, current, and voltage in real-world usage scenarios to evaluate energy efficiency.

[0004] However, existing testing methods have significant technical drawbacks. While integrating batteries into the vehicle or large energy storage unit for testing is closer to real-world conditions, it takes 1 to 2 months and costs over 100,000 RMB, severely hindering R&D efficiency and cost control. Furthermore, such testing processes are complex and time-consuming, making it difficult to meet the needs of rapid iteration in R&D. Summary of the Invention

[0005] In view of this, the present invention provides a method for evaluating battery operating condition energy efficiency, in order to solve the problems of long testing cycles and high costs in current battery operating condition energy efficiency evaluation methods.

[0006] This invention provides a method for evaluating the energy efficiency of a battery under operating conditions. The capacity of a battery cell is denoted as a (Ah), the full-charge cutoff voltage is denoted as B (V), the empty-charge cutoff voltage is denoted as C (V), the operating voltage is denoted as D (V), the charging power of a single battery cell is denoted as P1 (W), the charging power of the energy storage device is denoted as P (W), and the total number of battery cells contained in the energy storage device is X, where X≥1. When X≥2, the X battery cells are connected in series, and P1=P / X.

[0007] The battery operating condition energy efficiency assessment method includes the following steps:

[0008] Step S10: Let the battery cell stand still until its temperature reaches the test temperature T1 (in °C). The ambient temperature is T0 (in °C). T1 = T0 ± 2 °C.

[0009] Step S20, constant current charging to full cut-off voltage B at current I1, then constant voltage charging at full cut-off voltage B until the current drops to I2, determine full charge, stop charging; the unit of current is A;

[0010] Step S30, stand the battery cell, so that the temperature of the battery cell reaches the test temperature T1 again;

[0011] Step S40, constant current discharge to empty cut-off voltage C at current I3;

[0012] Step S50, stand the battery cell, so that the temperature of the battery cell reaches the test temperature T1 again;

[0013] Step S60, constant power charging to full cut-off voltage B at charging power P1, get the energy E1 of single battery cell, unit is Wh;

[0014] Step S70, stand the battery cell, so that the temperature of the battery cell reaches the test temperature T1 again;

[0015] Step S80, set the test working condition, discharge the battery cell to empty cut-off voltage C under the test working condition, get the net discharge energy E2 of single battery cell, unit is Wh;

[0016] Step S90, the energy efficiency of the battery cell under the test working condition is P3, P3=E2 / E1×100%.

[0017] Beneficial effects: the battery working condition energy efficiency evaluation method provided by the application simulates the complex working conditions of the battery in the actual use process, including temperature change, constant current and constant voltage charging mode and different discharge conditions, by carrying out multi-stage charging and discharging and standing treatment of a single cell under a specific working condition. The energy E1 of a single cell and the net discharge energy E2 of a single cell are quickly obtained through the constant power charging in step S60 and the discharge test under the test working condition in step S80, so that the energy efficiency P3 is calculated through P3=E2 / E1*100%. Since the battery working condition energy efficiency evaluation method provided by the application is tested at the cell level, it is not necessary to assemble the cells into a module, pack and place the whole vehicle or large energy storage cabinet, and the test cycle only needs 1 to 2 days. Compared with the test mode of integrating into a whole vehicle or large energy storage platform for a long time in the prior art, the method simplifies the test process, reduces the test time and economic cost, and is beneficial to improving the research and development efficiency and product iteration speed. At the same time, the energy efficiency P3 of the cell under the test working condition can be measured by the application, which truly reflects the problem of the working state of the battery system in the whole vehicle or large energy storage cabinet, and provides a more practical application technical means for the energy efficiency evaluation of large-scale battery system. According to the energy efficiency of the single cell, it is evaluated whether the battery system meets the requirements of the whole vehicle. In the case that the evaluation result does not meet the use demand of the whole vehicle, the researchers are guided to improve the battery system by adjusting the battery system, energy density or fast charging capacity and other factors, which greatly shortens the research and development time.

[0018] In an alternative embodiment, it is satisfied that a / 5≤I1≤2a / 5, a / 100≤I2≤a / 10.

[0019] In an alternative embodiment, it is satisfied that a / 5≤I3≤2a / 5.

[0020] In an alternative embodiment, in step S60, the charging time is T seconds, and the energy E1 of a single cell is determined according to the charging time-power curve.

[0021] In an alternative embodiment, the net discharge energy E2 of a single cell is obtained by integrating the discharge time-power curve.

[0022] In an alternative embodiment, the following steps are further included after step S80:

[0023] Step S81, standing the cell so that the temperature of the cell reaches the test temperature T1 again;

[0024] Step S82, constant current discharge at a current of I4 to the empty cut-off voltage C;

[0025] Step S83, standing the cell so that the temperature of the cell reaches the test temperature T1 again.

[0026] In an alternative embodiment, a / 5≤I4≤2a / 5 is satisfied.

[0027] In an alternative embodiment, in step S80, if the battery cell is not discharged to the empty cut-off voltage C under the test condition, the test condition is cycled again until the battery cell is discharged to the empty cut-off voltage C.

[0028] In an alternative embodiment, T0≤0℃, or 23℃≤T0≤27℃, or T0≥40℃.

[0029] In an alternative embodiment, the initial temperature of the battery cell is T2, in ℃,

[0030] When T2≤0℃ and T0≤0℃, the standing time of the battery cell is 20min~2h;

[0031] When T2≤0℃ and 23℃≤T0≤27℃, the standing time of the battery cell is 3h ~6h;

[0032] When T2≤0℃ and T0≥40℃, the standing time of the battery cell is 6~12h;

[0033] When 23℃≤T2≤27℃ and T0≤0℃, the standing time of the battery cell is 3h ~6h;

[0034] When 23℃≤T2≤27℃ and 23℃≤T0≤27℃, the standing time of the battery cell is 20min~2h;

[0035] When 23℃≤T2≤27℃ and T0≥40℃, the standing time of the battery cell is 3h ~6h;

[0036] When T2≥40℃ and T0≤0℃, the standing time of the battery cell is 6h ~12h;

[0037] When T2≥40℃ and 23℃≤T0≤27℃, the standing time of the battery cell is 3h ~6h;

[0038] When T2≥40℃ and T0≥40℃, the standing time of the battery cell is 20min~2h. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, hereinafter the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative effort.

[0040] Figure 1A flow chart of a battery operating condition energy efficiency evaluation method of an embodiment of the present application;

[0041] Figure 2 A charge time-power curve chart of implementation case 1 in the present application;

[0042] Figure 3 A discharge time-power curve chart of implementation case 1 in the present application;

[0043] Figure 4 A charge time-power curve chart of implementation case 2 in the present application;

[0044] Figure 5 A discharge time-power curve chart of implementation case 2 in the present application;

[0045] Figure 6 A charge time-power curve chart of implementation case 3 in the present application;

[0046] Figure 7 A discharge time-power curve chart of implementation case 3 in the present application;

[0047] Figure 8 A charge time-power curve chart of implementation case 4 in the present application;

[0048] Figure 9 A discharge time-power curve chart of implementation case 4 in the present application;

[0049] Figure 10 A charge time-power curve chart of implementation case 5 in the present application;

[0050] Figure 11 A discharge time-power curve chart of implementation case 5 in the present application;

[0051] Figure 12 A charge time-power curve chart of implementation case 6 in the present application;

[0052] Figure 13 A discharge time-power curve chart of implementation case 6 in the present application;

[0053] Figure 14 A flow chart of another battery operating condition energy efficiency evaluation method of an embodiment of the present application. DETAILED DESCRIPTION

[0054] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0055] The embodiments of the present application are described below in combination with Figures 1 to 14

[0056] According to the embodiments of the present application, a battery working condition energy efficiency evaluation method is provided. The capacity of a battery cell is a, in units of Ah, the full charge cut-off voltage is B, in units of V, the empty charge cut-off voltage is C, in units of V, the working voltage is D, in units of V, the charging power of a single battery cell is P1, in units of W, the charging power of an energy storage device is P, in units of W, the total number of battery cells included in the energy storage device is X, X≥1, when X≥2, the X battery cells are connected in series, and P1=P / X.

[0057] The battery working condition energy efficiency evaluation method comprises the following steps:

[0058] Step S10, the battery cell is left to stand so that the temperature of the battery cell reaches a test temperature T1, in units of ℃, and the ambient temperature is T0, in units of ℃, T1=T0±2 ℃;

[0059] Step S20, constant current charging is performed at a current I1 to the full charge cut-off voltage B, and then constant voltage charging is performed at the full charge cut-off voltage B until the current drops to I2, which is determined as full charging, and the charging is stopped; the unit of the current is A;

[0060] Step S30, the battery cell is left to stand so that the temperature of the battery cell again reaches the test temperature T1;

[0061] Step S40, constant current discharging is performed at a current I3 to the empty charge cut-off voltage C;

[0062] Step S50, the battery cell is left to stand so that the temperature of the battery cell again reaches the test temperature T1;

[0063] Step S60, constant power charging is performed at a charging power P1 to the full charge cut-off voltage B to obtain the energy E1 of a single battery cell, in units of Wh;

[0064] Step S70, the battery cell is left to stand so that the temperature of the battery cell again reaches the test temperature T1;

[0065] Step S80, a test working condition is set, and the battery cell is discharged to the empty charge cut-off voltage C under the test working condition to obtain the net discharge energy E2 of a single battery cell, in units of Wh; ​

[0066] Step S90, the energy efficiency of the battery cell under the test working condition is P3, P3=E2 / E1x100%.

[0067] The present application simulates the complex working conditions of the battery in actual use process by carrying out multi-stage charging and discharging and standing treatment of the single battery cell under specific working conditions, including temperature change, constant current and constant voltage charging mode and different discharging conditions.

[0068] The battery working condition energy efficiency evaluation method provided by the present application quickly obtains the two key parameters of the energy E1 of the single battery cell and the net discharging energy E2 of the single battery cell through the constant power charging in step S60 and the discharging test under the test working condition in step S80, so as to calculate the energy efficiency P3 through P3=E2 / E1x100%. Since the battery working condition energy efficiency evaluation method provided by the present application tests at the battery cell level, it is not necessary to assemble the battery cells into a module, pack and place in a whole vehicle or a large energy storage cabinet, and the test period only needs 1 to 2 days. Compared with the test mode of integrating into a whole vehicle or a large energy storage platform for a long time in the prior art, the present method simplifies the test process, reduces the test time and economic cost, and is beneficial to improving the research and development efficiency and product iteration speed. At the same time, the present application can measure the energy efficiency P3 of the battery cell under the test working condition, which truly reflects the problem of the working state of the battery system in the whole vehicle or the large energy storage cabinet, and provides a more practical application technical means for the energy efficiency evaluation of the large-scale battery system. According to the measured energy efficiency of the single battery cell, it is evaluated whether the battery system meets the requirements of the whole vehicle. In the case that the evaluation result does not meet the use requirements of the whole vehicle, the researchers are guided to improve the battery system by adjusting the battery system, energy density or fast charging capacity and other factors, which greatly shortens the research and development time.

[0069] In some embodiments, the following conditions are met: a / 5≤I1≤2a / 5, a / 100≤I2≤a / 10.

[0070] It should be noted that in the present embodiment, 1 / 5, 2 / 5, 1 / 100 and 1 / 10 all represent the rate, and the rate (C Rate) is a relative unit to describe the size of the charging and discharging current of the battery, which represents the multiple of the current relative to the capacity of the battery.

[0071] Charging and discharging current (A)=C Ratex battery capacity (Ah).

[0072] I1 is controlled between a / 5 and 2a / 5, and charging is performed at the constant current, which can avoid the problem of long charging time caused by too small current, and thus long test period and high test cost, and can also avoid the problem of low battery charging efficiency caused by too large current, and thus small temperature rise of the battery, thereby reducing the possibility of side reactions of the electrolyte, helping to maintain the stability of the battery chemical system, and avoiding damage to the internal structure of the battery caused by too large current, thereby improving the cycle life of the battery.

[0073] I1 is preferably a / 3, and charging is performed at the constant current, which can reduce the temperature rise of the battery and has moderate charging time.

[0074] I2 is controlled in the range of a / 100 to a / 10 in the constant voltage charging phase, which can ensure that the lithium intercalation speed of the negative electrode matches the charging process, effectively avoid the occurrence of lithium precipitation, and thus ensure the safety of the battery.

[0075] I2 is preferably a / 20, which can effectively eliminate the influence of battery polarization on the energy of the battery.

[0076] In some embodiments, a / 5≤I3≤2a / 5 is satisfied.

[0077] In the present embodiment, 1 / 5 and 2 / 5 both represent the rate.

[0078] I3 is controlled between a / 5 and 2a / 5, and charging is performed at the constant current, which can avoid the problem of long charging time caused by too small current, and thus long test period and high test cost, and can also avoid the problem of low battery charging efficiency caused by too large current, and thus small temperature rise of the battery, thereby reducing the possibility of side reactions of the electrolyte, helping to maintain the stability of the battery chemical system, and avoiding damage to the internal structure of the battery caused by too large current, thereby improving the cycle life of the battery.

[0079] I3 is preferably a / 3, and charging is performed at the constant current, which can reduce the temperature rise of the battery and has moderate charging time.

[0080] In some embodiments, in step S60, the charging time is T seconds, and the energy E1 of the single cell is determined according to the charging time-power curve.

[0081] The charging time-power curve describes the relationship between the power P and the time T in the charging process. The energy E1 stored in the cell is equal to the total electric energy input in the charging process, i.e. the integral of power with respect to time.

[0082] Determining the energy E1 of the single cell according to the charging time-power curve is more consistent with the dynamic characteristics of the actual charging process, and can provide more comprehensive and accurate energy evaluation.

[0083] In some embodiments, the net discharge energy E2 of the single cell is obtained by integrating the discharge time-power curve.

[0084] The discharge time-power curve describes the relationship between the power P and the time T during the discharge process. The net discharge energy E2 is the integral of the power with respect to time during the discharge process of the cell. Its physical meaning is the actual energy provided by the battery for the load.

[0085] The net discharge energy E2 of the single cell is obtained by integrating the discharge time-power curve, which is directly based on the real-time power (voltage x current) integrated with respect to time, and can accurately capture fluctuations (such as pulse load, transient response) in the charging and discharging process, avoiding errors of static parameters (such as nominal capacity).

[0086] By combining the net discharge energy E2 and the input energy E1, the cycle efficiency E2 / E1 can be calculated, which can quantify the energy loss (such as internal resistance heat consumption, side reaction) of the battery system.

[0087] In some embodiments, after step S80, the following steps are further included:

[0088] Step S81, resting the cell so that the temperature of the cell reaches the test temperature T1 again;

[0089] Step S82, constant current discharge at a current I4 to the empty cut-off voltage C;

[0090] Step S83, resting the cell so that the temperature of the cell reaches the test temperature T1 again.

[0091] Through steps S81 to S83, it can be quickly judged whether the change of the cell energy efficiency is caused by the polarization of the cell.

[0092] Steps S81 to S83 can be performed synchronously with step S90.

[0093] In some embodiments, a / 5≤I4≤2a / 5 is satisfied.

[0094] In this embodiment, 1 / 5 and 2 / 5 both represent the rate.

[0095] Controlling I4 between a / 5 and 2a / 5 to discharge at this constant current avoids the problem of too long discharge time caused by too small current, and prevents the increase of energy loss and the decrease of efficiency caused by too large current, thereby optimizing the energy utilization rate of the overall discharge process.

[0096] In some embodiments, in step S80, the test working condition includes a CLTC working condition or a WLCT working condition.

[0097] CLTC (China Light-duty Vehicle Test Cycle) is a Chinese light-duty vehicle test cycle developed primarily in China to more accurately reflect the energy consumption and range performance of vehicles in actual use within China.

[0098] CLTC tests are primarily conducted in a laboratory environment, with a test temperature of 20°C and an average test speed of approximately 48.3 km / h, including both urban and highway driving conditions, but with a greater emphasis on urban low and medium speed driving.

[0099] CLTC has a relatively low test speed, with a maximum speed of 114 km / h and an average speed of approximately 28.96 km / h, focusing more on urban driving scenarios.

[0100] WLTC (Worldwide Harmonized Light Vehicles Test Cycle) is a global harmonized light vehicle test cycle developed by organizations such as the European Union to adapt to different driving environments and vehicle technology developments around the world.

[0101] WLTC tests are conducted in actual road environments, with a test temperature ranging from 14°C to 23°C and a test speed gradually increasing from low to high, including various driving conditions in urban and suburban areas, with a wider speed range.

[0102] WLTC has a wider test speed range, with a maximum speed of 131.3 km / h and an average speed of 46.5 km / h, allowing for better evaluation of vehicle performance in different road conditions.

[0103] In some embodiments, in step S80, if the battery cell is not discharged to the empty cut-off voltage C in one test cycle, the test cycle is repeated until the battery cell is discharged to the empty cut-off voltage C.

[0104] Forcing discharge to the empty cut-off voltage C can fully evaluate the energy efficiency of the battery cell in the full SOC range (100%→0%), avoiding data loss in the low SOC interval due to test interruption (this interval usually has significant polarization and efficiency drop).

[0105] Deep discharge may cause lithium deposition or SEI rupture, and cycle testing can capture the impact of these irreversible losses on efficiency, reflecting the true decay characteristics.

[0106] All tests use the empty cut-off voltage C as the termination point, eliminating data bias caused by inconsistent discharge depth (DOD) and facilitating horizontal comparison of efficiency of different battery cells or different cycle numbers.

[0107] If the working condition is complex dynamic load (such as electric vehicle acceleration-braking cycle), multiple cycles can accumulate the energy loss in actual operation (such as internal resistance temperature rise, active material fatigue).

[0108] In some embodiments, T0≤0℃, or 23℃≤T0≤27℃, or T0≥40℃.

[0109] T0≤0℃ is a low-temperature environment, 23℃≤T0≤27℃ is a normal-temperature environment, and T0≥40℃ is a high-temperature environment. The battery working condition energy efficiency evaluation method provided by the application is suitable for low-temperature, normal-temperature and high-temperature three temperature ranges.

[0110] In some embodiments, the initial temperature of the battery cell is T2, in ℃, and the time required for the battery cell to recover from the initial temperature T2 to the test temperature T1 is as follows:

[0111] When T2≤0℃ and T0≤0℃, the battery cell standing time is 20min~2h;

[0112] When T2≤0℃ and 23℃≤T0≤27℃, the battery cell standing time is 3h ~6h;

[0113] When T2≤0℃ and T0≥40℃, the battery cell standing time is 6~12h;

[0114] When 23℃≤T2≤27℃ and T0≤0℃, the battery cell standing time is 3h ~6h;

[0115] When 23℃≤T2≤27℃ and 23℃≤T0≤27℃, the battery cell standing time is 20min~2h;

[0116] When 23℃≤T2≤27℃ and T0≥40℃, the battery cell standing time is 3h ~6h;

[0117] When T2≥40℃ and T0≤0℃, the battery cell standing time is 6h ~12h;

[0118] When T2≥40℃ and 23℃≤T0≤27℃, the battery cell standing time is 3h ~6h;

[0119] When T2≥40℃ and T0≥40℃, the battery cell standing time is 20min~2h.

[0120] In the battery working condition energy efficiency evaluation method provided by the application, the battery cell is subjected to standing treatment after each operation to recover to the set test temperature (T1=T0±2℃), so that the consistency of the test conditions is ensured, the influence of the initial temperature of the battery cell on the battery energy is reduced, and the accuracy of the test data is improved.

[0121] The standing time of the battery cell in the determination step S10, the determination step S30, the determination step S50, the determination step S70, the determination step S81 and the determination step S83 is determined according to the initial temperature T2 of the battery cell and the ambient temperature T0, so that the temperature of the battery cell reaches the test temperature T1.

[0122] The ambient temperature T0 or the initial temperature T2 of the battery cell is divided into three temperature sections, i.e. a low temperature, a normal temperature and a high temperature. The low temperature is less than or equal to 0℃, the normal temperature is about 25℃, and the high temperature is greater than or equal to 40℃.

[0123] The standing time of the battery cell is related to the initial temperature T2 of the battery cell and the ambient temperature T0. For details, refer to Table 1.

[0124] Table 1

[0125]

[0126] Specifically, the full charge cut-off voltage B, the empty charge cut-off voltage C and the working voltage D are different according to different battery systems. Two specific embodiments are provided below.

[0127] When the battery system is lithium iron phosphate, the full charge cut-off voltage B is 3.65V, the empty charge cut-off voltage C is 2V, and the working voltage D is in the range of 2V to 3.65V.

[0128] When the battery system is ternary, the full charge cut-off voltage B is 4.4V, the empty charge cut-off voltage C is 2.1V, and the working voltage D is in the range of 2.1V to 4.4V.

[0129] Specific test cases of the energy efficiency of the battery working condition are provided below.

[0130] In the implementation case 1, the capacity a of a single battery cell is 164.5Ah, the charging power P1 is 55.9W, and the full charge cut-off voltage B is 3.65V. The energy E1 of a single battery cell is determined according to the charging time-power curve as shown in Figure 2 . The net discharge energy E2 of a single battery cell is obtained by integrating the discharge time-power curve as shown in Figure 3 .

[0131] In the implementation case 2, the capacity a of a single battery cell is 164.5Ah, the charging power P1 is 55.9W, and the full charge cut-off voltage B is 3.65V. The energy E1 of a single battery cell is determined according to the charging time-power curve as shown in Figure 4 . The net discharge energy E2 of a single battery cell is obtained by integrating the discharge time-power curve as shown in Figure 5 .

[0132] In the implementation case 3, the capacity a of the single cell is 164.5 Ah, the charging power P1 is 55.9 W, and the full-charge cut-off voltage B is 3.65 V. The energy E1 of the single cell is determined according to the charging time-power curve as shown in Figure 6 . The net discharge energy E2 of the single cell is integrated according to the discharge time-power curve as shown in Figure 7 .

[0133] In the implementation case 4, the capacity a of the single cell is 135.5 Ah, the charging power P1 is 58.9 W, and the full-charge cut-off voltage B is 3.65 V. The energy E1 of the single cell is determined according to the charging time-power curve as shown in Figure 8 . The net discharge energy E2 of the single cell is integrated according to the discharge time-power curve as shown in Figure 9 .

[0134] In the implementation case 5, the capacity a of the single cell is 135.5 Ah, the charging power P1 is 58.9 W, and the full-charge cut-off voltage B is 3.65 V. The energy E1 of the single cell is determined according to the charging time-power curve as shown in Figure 10 . The net discharge energy E2 of the single cell is integrated according to the discharge time-power curve as shown in Figure 11 .

[0135] In the implementation case 6, the capacity a of the single cell is 135.5 Ah, the charging power P1 is 58.9 W, and the full-charge cut-off voltage B is 3.65 V. The energy E1 of the single cell is determined according to the charging time-power curve as shown in Figure 12 . The net discharge energy E2 of the single cell is integrated according to the discharge time-power curve as shown in Figure 13 .

[0136] The energy E1 of the single cell, the net discharge energy E2 of the single cell, and the cell energy efficiency P3 of the implementation cases 1 to 6 are shown in Table 2.

[0137] Table 2

[0138]

[0139] According to the calculated P3, whether the current test battery meets the use requirements can be evaluated according to the application requirements in different application scenarios.

[0140] For example, the lithium ion battery is applied in power energy storage or electric vehicles. The power energy storage system requires an initial energy efficiency ≥ 92%, and the power battery system of the electric vehicle is usually ≥ 90%. After 500 cycles, the discharge energy retention rate is ≥ 90%. The energy efficiency ≥ 95% is excellent. The cell working condition energy efficiency of the above-mentioned implementation cases 1 to 6 is excellent.

[0141] The battery working condition energy efficiency evaluation method provided by the application can test the battery cell level (one or more series) and greatly shorten the test period and reduce the test cost.

[0142] Although the embodiments of the present application are described in conjunction with the drawings, various modifications and changes can be made by those skilled in the art without departing from the spirit and scope of the present application, and such modifications and changes fall within the scope defined by the appended claims.

Claims

1. A method for evaluating battery energy efficiency under operating conditions, characterized in that, The capacity of a battery cell is a, in Ah; the fully charged cutoff voltage is B, in V; the empty cutoff voltage is C, in V; the operating voltage is D, in V; the charging power of a single battery cell is P1, in W; the charging power of the energy storage device is P, in W; the total number of battery cells in the energy storage device is X, where X ≥ 1; when X ≥ 2, the X battery cells are connected in series; and P1 = P / X. The battery operating condition energy efficiency evaluation method includes the following steps: Step S10: Let the battery cell stand still until its temperature reaches the test temperature T1 (in °C). The ambient temperature is T0 (in °C). T1 = T0 ± 2 °C. Step S20: Charge at a constant current of I1 until the full charge cutoff voltage B, then switch to constant voltage charging at the full charge cutoff voltage B until the current drops to I2, at which point it is determined to be fully charged and charging is stopped; the unit of current is A. Step S30: Let the battery cell stand still so that its temperature reaches the test temperature T1 again. Step S40: Discharge at a constant current of I3 until the open circuit cutoff voltage C is reached; Step S50: Let the battery cell stand still to allow its temperature to reach the test temperature T1 again. Step S60: Charge the battery to the full charge cutoff voltage B at a constant power of P1 to obtain the energy E1 of a single cell, in Wh. Step S70: Let the battery cell stand still to allow its temperature to reach the test temperature T1 again. Step S80: Set the test conditions. Under the test conditions, discharge the battery cell to the empty cutoff voltage C to obtain the net discharge energy E2 of a single battery cell, in Wh. Step S90: The energy efficiency of the battery cell under test conditions is P3, where P3 = E2 / E1 × 100%. The initial temperature of the battery cell is T2, in °C. When T2≤0℃ and T0≤0℃, the cell resting time is 20min~2h; When T2≤0℃ and 23℃≤T0≤27℃, the cell resting time is 3h ~ 6h; When T2≤0℃ and T0≥40℃, the cell resting time is 6~12h; When 23℃≤T2≤27℃ and T0≤0℃, the cell resting time is 3h ~6h; When the temperature is 23℃≤T2≤27℃ and 23℃≤T0≤27℃, the cell resting time is 20min~2h. When 23℃≤T2≤27℃ and T0≥40℃, the cell resting time is 3h ~6h; When T2≥40℃ and T0≤0℃, the cell resting time is 6h ~12h; When T2≥40℃ and 23℃≤T0≤27℃, the cell resting time is 3h ~6h; When T2≥40℃ and T0≥40℃, the cell resting time is 20min~2h.

2. The battery operating condition energy efficiency evaluation method according to claim 1, characterized in that, satisfy: a / 5≤I1≤2a / 5, a / 100≤I2≤a / 10.

3. The battery operating condition energy efficiency evaluation method according to claim 1 or 2, characterized in that, satisfy: a / 5≤I3≤2a / 5.

4. The battery operating condition energy efficiency evaluation method according to claim 1 or 2, characterized in that, In step S60, the charging time is T seconds, and the energy E1 of a single cell is determined according to the charging time-power curve.

5. The battery operating condition energy efficiency evaluation method according to claim 1 or 2, characterized in that, The net discharge energy E2 of a single cell is obtained by integrating the discharge time-power curve.

6. The battery operating condition energy efficiency evaluation method according to claim 1 or 2, characterized in that, The following steps are included after step S80: Step S81: Let the battery cell stand still so that its temperature reaches the test temperature T1 again. Step S82: Discharge at a constant current of I4 until the open circuit cutoff voltage C is reached; Step S83: Let the battery cell stand still so that its temperature reaches the test temperature T1 again.

7. The battery operating condition energy efficiency evaluation method according to claim 6, characterized in that, satisfy: a / 5≤I4≤2a / 5.

8. The battery operating condition energy efficiency evaluation method according to claim 1 or 2, characterized in that, In step S80, if the cell does not discharge to the empty cutoff voltage C under a test condition, the test condition is repeated until the cell discharges to the empty cutoff voltage C.

9. The battery operating condition energy efficiency evaluation method according to claim 1 or 2, characterized in that, T0≤0℃, or 23℃≤T0≤27℃, or T0≥40℃.

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