Test method and equipment for widening charging boundary of battery

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a test method and device for widening the charging boundary of a battery. The related test method comprises the following steps: acquiring the maximum charging rate of a battery under 0% SOC, charging the battery through the maximum charging rate, and monitoring the temperature value of the battery in real time; when the battery reaches the x% SOC at any moment and the difference value between the temperature value of the battery under the x% SOC and the temperature value of the battery under the 0% SOC reaches a preset value, the maximum charging rate of the battery under the x% SOC is obtained again, and the battery is charged until the battery is fully charged; wherein 0 lt; and x is less than or equal to 100. According to the test method, the temperature of the battery in the charging process can be monitored in real time, when the temperature change is large, the charging rate of the battery is adjusted, the accuracy of the charging boundary test can be improved, and a tester can quickly determine a reasonable charging parameter range and carry out experiments and optimization in a targeted mode.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a testing method and device for broadening the battery charging boundary. Background Art

[0002] With the increasing popularity of electric vehicles, demands for faster charging performance and safety are becoming increasingly stringent. Determining the lithium plating boundary through three-electrode testing can optimize charging strategies, increasing charging speed while preventing lithium plating, extending battery life, and improving the user experience and safety of electric vehicles.

[0003] Initially, determining lithium deposition by simply monitoring the negative electrode potential has evolved to combining multiple analytical methods, such as capacity-voltage differential data, to more accurately determine the boundaries of lithium deposition, identifying specific points to determine the deposition voltage and capacity. The accuracy and functionality of testing equipment has also continued to improve. Power battery cell testing systems with higher current and voltage control and detection accuracy can more accurately capture subtle changes in voltage and current.

[0004] However, the existing battery charging boundary test process does not take into account the impact of temperature rise during the actual charging process of the battery, resulting in a certain difference between the test boundary and the boundary in the actual application process. Summary of the Invention

[0005] Embodiments of the present invention provide a testing method and device for broadening the battery charging boundary, so as to solve the technical problem in the prior art that, during the battery charging boundary testing process, the influence of the temperature rise during the actual charging process of the battery is not taken into account, resulting in a difference between the test boundary and the boundary during actual application.

[0006] In a first aspect, an embodiment of the present invention provides a testing method for broadening a battery charging boundary, comprising:

[0007] Obtaining a maximum charge rate of a battery at 0% SOC, charging the battery at the maximum charge rate, and monitoring a temperature value of the battery in real time;

[0008] At any moment, when the battery reaches x% SOC, when the difference between the battery temperature at x% SOC and the battery temperature at 0% SOC reaches a preset value, the maximum charge rate of the battery at x% SOC is re-obtained, and the battery is charged until it is fully charged; wherein 0 <x≤100。

[0009] In an optional implementation manner, charging the battery at a maximum charge rate includes:

[0010] Charging the battery at a maximum charge rate of the battery at 0% SOC;

[0011] When the battery is charged to the cut-off voltage, the charging rate is gradually reduced until the battery is fully charged.

[0012] In an optional embodiment, before gradually reducing the charge rate when charging to the cut-off voltage of the battery, the method further includes:

[0013] After charging to the cut-off voltage at the maximum charge rate, stop charging and let it stand;

[0014] After the rest period is reached, the charging rate is gradually reduced until the battery is fully charged.

[0015] In an optional embodiment, the gradually reducing the charging rate includes reducing the charging rate in stages, and preferably, the step size of the step reduction is 0.02C to 0.1C;

[0016] And / or, the standing time is 8s to 20s.

[0017] In an optional embodiment, when the difference between the temperature value of the battery at the x% SOC and the temperature value at the 0% SOC reaches a preset value, re-obtaining the maximum charge rate at the x% SOC includes:

[0018] During the charging process, obtaining x1% SOC and a first temperature value of the battery at a first moment, and x2% SOC and a second temperature value at a second moment; wherein x1≠x2;

[0019] When the difference between the first temperature value and the second temperature value is greater than or equal to the preset value, the maximum charging rate is changed, and charging is performed at the changed maximum charging rate.

[0020] In an optional implementation manner, changing the maximum charge rate and charging at the changed maximum charge rate includes:

[0021] Obtaining the x1% SOC and the first temperature value of the battery at the first moment, and the maximum charge rate corresponding to the x1% SOC; and the x2% SOC and the second temperature value at the second moment;

[0022] When the difference between the first temperature value and the second temperature value is greater than or equal to the preset value, the maximum charging rate corresponding to the battery at the x2% SOC is recalculated and obtained, and the battery is charged.

[0023] In an optional implementation manner, the method for obtaining the maximum charge rate includes:

[0024] Measuring the open circuit voltage of the battery at different states of charge to determine the internal resistance of the battery;

[0025] charging the battery with different charging currents, and measuring the polarization voltages corresponding to the different charging currents;

[0026] A functional relationship model is established based on the internal resistance, charging current and polarization voltage, and the maximum charging rate is obtained through data fitting.

[0027] In an optional implementation manner, the functional relationship model includes a linear functional relationship model or a quadratic functional relationship model;

[0028] The data fitting includes the following test conditions according to the polarization voltage:

[0029] OCV(SOC)+I×R Ω +Vp(I)=V cutoff ;

[0030] The charging current is increased. When the equation of the polarization voltage test condition is satisfied and the negative parameter potential is greater than or equal to 0, the charging current is the maximum charging rate.

[0031] In an optional implementation manner, the functional relationship model is Vp(I)=k(SOC)×I+b(SOC);

[0032] Where, I represents the charging current, Vp(I) represents the polarization voltage, and V cutoff represents the charge cut-off voltage, k(SOC) and b(SOC) represent the correlation coefficients.

[0033] In a second aspect, an embodiment of the present invention provides a test device for broadening a battery charging boundary, including:

[0034] A charging device, used to obtain the maximum charging rate of the battery in an empty state, charge the battery at the maximum charging rate, and monitor the temperature of the battery in real time;

[0035] The monitoring device is used to re-obtain the maximum charging rate of the battery when the temperature change value of the battery reaches a preset value.

[0036] The implementation of the technical solution of the present invention has at least the following beneficial effects:

[0037] A test method and device for broadening the battery charging boundary provided by an embodiment of the present invention obtain the maximum charging rate of the battery at 0% SOC, charge the battery at the maximum charging rate, and monitor the temperature value of the battery in real time; at any moment when the battery reaches x% SOC, when the difference between the temperature value of the battery at x% SOC and the temperature value of the battery at 0% SOC reaches a preset value, re-obtain the maximum charging rate of the battery at x% SOC and charge the battery until it is fully charged; where 0 < x ≤ 100. The test method of the present invention can monitor the temperature of the battery in real time during the charging process. When the temperature changes greatly, adjust the charging rate of the battery, which can improve the accuracy of the charging boundary test, enable the tester to quickly determine a reasonable charging parameter range, and conduct experiments and optimizations targeted.

[0038] Additional aspects and advantages of the present invention will be given in part in the following description, will become apparent in part from the following description, or will be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings herein are incorporated into the specification and constitute a part of the specification, showing embodiments consistent with the present invention, and are used together with the specification to explain the principles of the present invention.

[0040] Figure 1 The flowchart of the test method for broadening the battery charging boundary provided by an embodiment of the present invention is shown. Figure 1 ;

[0041] Figure 2 The flowchart of the test method for expanding the battery charging boundary provided by an embodiment of the present invention is shown. Figure 2 ;

[0042] Figure 3 The flowchart of the test method for expanding the battery charging boundary provided by an embodiment of the present invention is shown. Figure 3 ;

[0043] Figure 4 The structural schematic diagram of the test device for expanding the battery charging boundary provided by an embodiment of the present invention is shown;

[0044] Figure 5 The test for expanding the battery charging boundary provided by an embodiment of the present invention is shown Figure 1 ;

[0045] Figure 6 The test for expanding the battery charging boundary provided by an embodiment of the present invention is shown Figure 2 .

[0046] The above drawings illustrate specific embodiments of the present invention, which will be described in more detail below. These drawings and the accompanying description are not intended to limit the scope of the present invention in any way, but rather to illustrate the concept of the present invention to those skilled in the art by reference to specific embodiments. DETAILED DESCRIPTION

[0047] The present invention will be further described below with reference to specific examples. It should be understood that these examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0048] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range or the individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0049] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0050] Unless otherwise specified, all technical features and optional technical features of the present invention can be combined with each other to form a new technical solution.

[0051] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0052] Unless otherwise specified, the terms "include" and "comprising" used in the present invention may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0053] First, the nouns appearing in the present invention are explained:

[0054] SOC: The battery's state of charge (SOC) refers to the remaining charge in the battery, typically expressed as a percentage. The most classic definition of SOC is: SOC = Qremain / Qrated × 100%.

[0055] The depth of charge of a battery at different charge rates is a crucial factor in developing a fast-charging system. Testing the battery's charge boundary ensures safe fast-charging and prevents lithium deposition. However, existing fast-charging boundary testing often fails to account for the increase in battery temperature during the charging process. As battery temperature rises, internal changes occur within the battery, leading to deviations between test results and actual application. This can make lithium deposition and other safety incidents more likely to occur during real-world fast charging.

[0056] In view of this, the embodiments of the present application provide a testing method for broadening the battery charging boundary, fully considering the battery temperature rise during the charging process, improving the accuracy of the charging boundary test, and ensuring that the occurrence of accidents such as lithium plating is reduced during the actual application of the battery.

[0057] Figure 1 A test method process for broadening battery charging boundaries provided by an embodiment of the present invention Figure 1 .like Figure 1 As shown, an embodiment of the present invention provides a test method for broadening the battery charging boundary, including:

[0058] S101 . Obtain a maximum charge rate of a battery at 0% SOC, charge the battery at the maximum charge rate, and monitor the battery temperature in real time.

[0059] The maximum charge rate varies depending on the battery type. Specifically, the maximum charge rate varies depending on the battery's material, structure, and manufacturer. A battery's empty state typically refers to a state where the battery's charge is close to zero or completely depleted. A battery can be a single cell or multiple cells. When the battery is empty, it can be charged using any of the following methods: constant voltage charging, constant current charging, or trickle charging.

[0060] During the charging process, the battery temperature rises due to the electrochemical reaction that occurs inside the battery, which is usually an exothermic reaction. In some embodiments of the present invention, a temperature monitoring device is used to monitor the battery temperature in real time during the charging process.

[0061] S102. At any moment, when the battery reaches x% SOC, and when the difference between the temperature value of the battery at x% SOC and the temperature value of the battery at 0% SOC reaches a preset value, re-obtain the maximum charging rate of the battery at x% SOC, and charge the battery until it is full; where 0 < x ≤ 100.

[0062] The preset value is set by the tester. When the difference ΔT between the temperature values at any two moments is greater than or equal to this preset value, the maximum charging rate corresponding to x% SOC at this temperature value will be re-obtained, and the battery will be charged at this maximum charging rate.

[0063] Exemplarily, during the battery charging process, at time t1, obtain the maximum charging rate of the battery at 0% SOC to charge the battery, and obtain the temperature value T1 at time t1; at time t2, obtain the temperature value T2, and the battery reaches x% SOC. If the absolute value of T2 - T1 is greater than or equal to the preset value ΔT, then obtain the maximum charging rate at x% SOC, and charge the battery at this maximum charging rate. In this way, it is possible to fully consider the battery temperature rise during the actual charge and discharge process, improve the accuracy of the charging boundary test, ensure that in the actual application process of the battery, reduce lithium plating, etc.

[0064] A test method and device for broadening the battery charging boundary provided by an embodiment of the present invention. The involved test method obtains the maximum charging rate of the battery at 0% SOC, charges the battery through the maximum charging rate, and monitors the temperature value of the battery in real time; at any moment when the battery reaches x% SOC, when the difference between the temperature value of the battery at x% SOC and the temperature value of the battery at 0% SOC reaches a preset value, re-obtain the maximum charging rate of the battery at x% SOC, and charge the battery until it is full; where 0 < x ≤ 100. The test method of the present invention can monitor the temperature of the battery in real time during the charging process. When the temperature changes greatly, adjust the charging rate of the battery, which can improve the accuracy of the charging boundary test, enable the tester to quickly determine a reasonable charging parameter range, and conduct experiments and optimizations targeted.

[0065] Figure 2 This is a flowchart of a test method for broadening the battery charging boundary provided by an embodiment of the present invention Figure 1 . As Figure 2 shown, charging the battery through the maximum charging rate includes:

[0066] S201. Charge the battery at the maximum charging rate of the battery at 0% SOC.

[0067] S202. After charging to the cut-off voltage at the maximum charging rate, stop charging and let it stand.

[0068] The battery is charged at the maximum charge rate when in an empty state. In some embodiments of the present invention, if the temperature difference between two moments during the charging process of the monitored battery is less than a preset value, the battery is charged at the initial maximum charge rate until the battery cut-off voltage is reached, and then charging is stopped and left to stand for a period of time.

[0069] Exemplarily, during the charging process, at a certain SOC of the battery at time t1, the maximum charging rate of the battery is obtained, and the battery is charged, and the temperature value T1 is obtained at time t1, and the temperature value T3 is obtained at time t3, and the temperature difference between T1 and T3 is less than a preset value; and at time t3 or before time t3, the cut-off voltage of the battery charging is reached, then at time t3 or before time t3, when the cut-off voltage is reached, charging is stopped and left to stand for a period of time.

[0070] S203. After the rest period is reached, gradually reduce the charging rate until the battery is fully charged.

[0071] After step S202, the rest period is reached and the charge rate is gradually reduced. This can be done in any manner, either regularly or irregularly, such as by gradually reducing the charge rate until the battery is fully charged. This method protects the battery from damage and effectively expands the scope of battery charging testing.

[0072] In some embodiments of the present invention, gradually reducing the charging rate includes reducing the charging rate in stages. Preferably, the step size of the stage-by-stage reduction is 0.02C to 0.1C.

[0073] Specifically, the step size of the step-by-step reduction can be 0.02C, 0.03C, 0.04C, 0.05C, 0.06C, 0.07C, 0.08C, 0.09C or 0.1C. Within this range, firstly, the charging efficiency can be improved: in the early stage of charging, the battery power is low, and charging with a larger current can quickly replenish the battery power and shorten the charging time. Secondly, it can protect the battery: excessively high charging current may cause damage to the battery, such as causing battery overheating and accelerated battery aging. Step-by-step current reduction charging can automatically adjust the current size according to the battery's charging status, providing a larger current when the battery power is low to meet the fast charging requirements, and reducing the current when the battery power is close to full to avoid overcharging, thereby effectively protecting the battery and extending the battery life. Step-by-step current reduction charging strikes a balance between speed, life and safety by dynamically adjusting the current, and is particularly suitable for fast charging scenarios of high energy density batteries.

[0074] Furthermore, the resting time is 8s to 20s. Specifically, the resting time can be 8s, 9s, 10s, 11s, 13s, 14s, 15s, 16s, 17s, 18s, 19s or 20s. Within this range, polarization is effectively reduced and electrode stress is relieved.

[0075] Figure 3 A test method process for broadening battery charging boundaries provided by an embodiment of the present invention Figure 3 .like Figure 3 As shown, when the difference between the temperature value of the battery at x% SOC and the temperature value at 0% SOC reaches a preset value, the maximum charge rate at x% SOC is obtained again, including:

[0076] S301 : During the charging process, obtain a x1% SOC and a first temperature value of the battery at a first moment, and a x2% SOC and a second temperature value of the battery at a second moment.

[0077] The first moment and the second moment may refer to any two moments in the battery charging process, where the state of charge of the battery at the two moments is x1% SOC and x2% SOC respectively; the first temperature value refers to the battery temperature value measured at the first moment, and the second temperature value refers to the battery temperature value measured at the second moment.

[0078] S302: When the difference between the first temperature value and the second temperature value is greater than or equal to a preset value, recalculate and obtain the maximum charging rate corresponding to the battery at x2% SOC, and charge the battery.

[0079] When the difference between the first temperature value and the second temperature value is greater than or equal to a preset value, it is necessary to re-acquire the maximum charge rate of the battery state of charge x2% SOC at the second temperature value, and charge at the maximum charge rate; in some embodiments of the present invention, when the difference between the first temperature value and the second temperature value is less than a preset value, and after charging to the cut-off voltage, the charge rate is gradually reduced. For example Figure 5 and Figure 6 ,in Figure 5 This is a test chart of the temperature rise during the charging process of the battery cells in the vehicle. Figure 6 This is a side view of the charge boundary comparison before and after coupling temperature; Figure 5 As shown in the figure, the battery on the whole vehicle will produce temperature rise during the charging process, and the temperature rise is different from the temperature rise of the soft-pack battery cell in the three-electrode test. Therefore, in order to obtain the impact of the real temperature rise on the charging boundary of the three-electrode battery, the battery cell is placed in a constant temperature box in the three-electrode test, and the temperature of the box is used to heat (or cool) the battery cell to simulate the real temperature rise.

[0080] Because the temperature of the battery cell rises differently inside and outside during charging, multiple temperature sensors must be installed inside the battery. The orange curve in the figure is the maximum temperature of the battery cell, and the yellow curve is the minimum temperature of the battery cell.

[0081] like Figure 6As shown in the figure, the dotted line is the charging boundary measured by three electrodes at 25°C under the uncoupled temperature rise condition, and the solid line is the three-electrode charging boundary obtained after coupling the actual temperature rise of the battery cell when charging on the whole vehicle.

[0082] In some embodiments of the present invention, the method for obtaining the maximum charging rate includes:

[0083] Measure the open circuit voltage of the battery at different states of charge to determine the internal resistance of the battery;

[0084] The battery is charged with different charging currents, and the polarization voltage corresponding to different charging currents is measured.

[0085] A functional relationship model is established based on the internal resistance, charging current and polarization voltage, and the maximum charging rate is obtained through data fitting.

[0086] In some embodiments of the present invention, the functional relationship model includes a linear functional relationship model or a quadratic functional relationship model;

[0087] Data fitting includes polarization voltage test conditions according to:

[0088] OCV(SOC)+I×R Ω +Vp(I)=V cutoff ;

[0089] Increase the charging current. When the equation for the polarization voltage test condition is met and the negative parameter potential is greater than or equal to 0, the charging current is the maximum charging rate.

[0090] In some embodiments of the present invention, the functional relationship model is Vp(I)=k(SOC)×I+b(SOC);

[0091] Where, I represents the charging current, Vp(I) represents the polarization voltage, and V cutoff represents the charge cut-off voltage, k(SOC) and b(SOC) represent the correlation coefficients.

[0092] Figure 4 The present invention provides a schematic diagram of a test device structure for broadening the battery charging boundary. Figure 4 As shown, an embodiment of the present invention provides a test device for broadening the battery charging boundary, including:

[0093] The charging device 401 is used to obtain the maximum charging rate of the battery in an empty state, charge the battery at the maximum charging rate, and monitor the battery temperature in real time.

[0094] The monitoring device 402 is used to re-acquire the maximum charge rate of the battery when the temperature change value of the battery reaches a preset value.

[0095] The charging device 401 is further used to charge the battery at the maximum charging rate when the battery is in an empty state;

[0096] When charging to the battery's cut-off voltage, gradually reduce the charging rate until the battery is fully charged.

[0097] The charging device 401 is further configured to charge the battery at a maximum charging rate to a cut-off voltage, then stop charging and allow the battery to rest;

[0098] After the rest period is reached, gradually reduce the charging rate until the battery is fully charged.

[0099] The monitoring device 402 is further configured to obtain a first temperature value of the battery at a first moment and a second temperature value of the battery at a second moment during the charging process;

[0100] When the difference between the first temperature value and the second temperature value is greater than or equal to a preset value, the maximum charging rate is changed, and charging is performed at the changed maximum charging rate.

[0101] The monitoring device 402 is further configured to obtain a first temperature value and a first maximum charge rate of the battery at a first moment, and a second temperature value at a second moment;

[0102] When the difference between the first temperature value and the second temperature value is greater than or equal to a preset value, the second maximum charging rate corresponding to the battery at the second temperature value is recalculated and obtained, and the battery is charged at the second maximum charging rate.

[0103] Parts of the present invention that are not described in detail are well known to those skilled in the art.

[0104] The basic principles of the present invention have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, and effects mentioned in the present invention are merely illustrative and non-limiting, and should not be construed as necessarily possessed by each embodiment of the present invention. Furthermore, the specific details disclosed above are provided for illustrative purposes and to facilitate understanding, and are not intended to be limiting. These details do not necessarily limit the present invention to being implemented using these specific details.

[0105] It should be noted that the terms "and / or" or " / " used herein are merely a description of an association relationship between associated objects, indicating that three relationships may exist. For example, A and / or B may represent three situations: A exists alone, A and B exist at the same time, and B exists alone. The singular forms "a," "the," and "the" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0106] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0107] If the integrated unit / module is implemented in hardware, the hardware may be digital circuits, analog circuits, etc. The physical implementation of the hardware structure includes, but is not limited to, transistors, memristors, etc. Unless otherwise specified, the processor may be any appropriate hardware processor, such as a CPU, GPU, FPGA, DSP, and ASIC. Unless otherwise specified, the storage unit may be any appropriate magnetic storage medium or magneto-optical storage medium, such as resistive random access memory (RRAM), dynamic random access memory (DRAM), static random access memory (SRAM), enhanced dynamic random access memory (EDRAM), high-bandwidth memory (HBM), hybrid memory cube (HMC), etc.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A test method for broadening the battery charging boundary, characterized in that: include: Obtaining a maximum charge rate of a battery at 0% SOC, charging the battery at the maximum charge rate, and monitoring a temperature value of the battery in real time; At any moment, when the battery reaches x% SOC, when the difference between the battery temperature at x% SOC and the battery temperature at 0% SOC reaches a preset value, the maximum charge rate of the battery at x% SOC is re-obtained, and the battery is charged until it is fully charged; wherein, 0 <x≤100。 2. The testing method according to claim 1, wherein: Charging the battery at the maximum charging rate includes: Charging the battery at a maximum charge rate of the battery at 0% SOC; When the battery is charged to the cut-off voltage, the charging rate is gradually reduced until the battery is fully charged.

3. The testing method according to claim 2, wherein: Before gradually reducing the charging rate when charging to the cut-off voltage of the battery, the method further includes: After charging to the cut-off voltage at the maximum charge rate, stop charging and let it stand; After the rest period is reached, the charging rate is gradually reduced until the battery is fully charged.

4. The testing method according to claim 2 or 3, characterized in that: The gradually reducing the charging rate includes reducing the charging rate in stages. Preferably, the step size of the step reduction is 0.02C to 0.1C. And / or, the standing time is 8s to 20s.

5. The testing method according to claim 1, wherein: When the difference between the temperature value of the battery at the x% SOC and the temperature value at the 0% SOC reaches a preset value, re-obtaining the maximum charge rate at the x% SOC includes: During the charging process, obtaining a x1% SOC and a first temperature value of the battery at a first moment, and a x2% SOC and a second temperature value at a second moment; When the difference between the first temperature value and the second temperature value is greater than or equal to the preset value, the maximum charging rate is changed, and charging is performed at the changed maximum charging rate.

6. The testing method according to claim 5, characterized in that: Changing the maximum charge rate and charging at the changed maximum charge rate includes: Obtaining the x1% SOC and the first temperature value of the battery at the first moment, and the maximum charge rate corresponding to the x1% SOC; the x2% SOC and the second temperature value at the second moment; wherein x1≠x2; When the difference between the first temperature value and the second temperature value is greater than or equal to the preset value, the maximum charging rate corresponding to the battery at the x2% SOC is recalculated and obtained, and the battery is charged.

7. The testing method according to claim 1, wherein: The method for obtaining the maximum charging rate includes: Measuring the open circuit voltage of the battery at different states of charge to determine the internal resistance of the battery; charging the battery with different charging currents, and measuring the polarization voltages corresponding to the different charging currents; A functional relationship model is established based on the internal resistance, charging current and polarization voltage, and the maximum charging rate is obtained through data fitting.

8. The testing method according to claim 7, characterized in that: The functional relationship model includes a linear functional relationship model or a quadratic functional relationship model; The data fitting includes the following test conditions according to the polarization voltage: OCV(SOC)+I×R Ω +Vp(I)=V cutoff ; The charging current is increased. When the equation of the polarization voltage test condition is satisfied and the negative parameter potential is greater than or equal to 0, the charging current is the maximum charging rate.

9. The testing method according to claim 8, characterized in that: The functional relationship model is Vp(I)=k(SOC)×I+b(SOC); Where, I represents the charging current, Vp(I) represents the polarization voltage, and V cutoff represents the charge cut-off voltage, k(SOC) and b(SOC) represent the correlation coefficients.

10. A test device for broadening the battery charging boundary, characterized in that: include: A charging device, used to obtain the maximum charging rate of the battery in an empty state, charge the battery at the maximum charging rate, and monitor the temperature of the battery in real time; The monitoring device is used to re-obtain the maximum charging rate of the battery when the temperature change value of the battery reaches a preset value.

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