Method and device for prolonging high-rate discharge duration of lithium ion battery

Abstract

The invention discloses a method and a device for prolonging high-rate discharge duration of a lithium ion battery. The invention discloses a method for prolonging high-rate discharge duration of a lithium ion battery. The method comprises the following steps: monitoring the current charge state of the lithium ion battery and the real-time temperature of the lithium ion battery in real time; comparing the real-time temperature of the lithium ion battery with the optimal discharge temperature corresponding to the current state of charge of the lithium ion battery; and according to the comparison result, cooling, heat preservation or heating is performed on the lithium ion battery, so that the temperature of the lithium ion battery is adjusted, and the lithium ion battery realizes minimum polarization and maximum long-multiplying-power continuous discharge time when discharging at the limit multiplying power in different charge states. According to the invention, the exerting efficiency of the battery power capability is improved, and the high-rate discharge duration of the lithium ion battery is effectively prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a method and device for extending the duration of high-rate discharge of lithium-ion batteries. Background Art

[0002] With the diversified development of the application scenarios of lithium-ion batteries, the market has higher and higher requirements for the comprehensive performance of lithium-ion batteries. It not only needs to have a high energy density to increase the cruising range, but also needs to have a high power capability to meet the instantaneous high traction requirements of electrical appliances. For example, electric aircraft, supercars, ship power systems, etc. all have similar requirements.

[0003] Currently, there are two methods to improve the power capability of lithium-ion batteries and extend the duration of their high-rate discharge: ① System design: Select appropriate electrolyte and electrode materials to improve the conductivity and ion transport rate of the battery. ② Charge and discharge regime: Adopt appropriate charging and discharging strategies to reduce the influence of battery polarization. Improving the power capability by changing the system design through method ① is likely to sacrifice other performance of the battery, such as energy density, high-temperature storage, cycle life, etc. In addition, it cannot be directly applied to existing products on the market and needs to go through a long process from design to finalization, with a relatively long overall development cycle. The method of improving the power capability by modifying the charge and discharge regime through method ② is also limited, because often the appropriate power consumption strategy does not match the actual working conditions and cannot be adjusted due to objective conditions.

[0004] Therefore, how to break through the limitations of battery system design, reduce the polarization phenomenon of lithium-ion batteries, further improve the efficiency of battery power capability, and thus extend the duration of its high-rate discharge to meet the requirements of high specific energy, high power and other comprehensive performance indicators of lithium-ion batteries in diverse application scenarios has become a technical problem that must be solved.

[0005] Chinese patent document CN104466236A discloses an energy and power balanced lithium-ion battery and its preparation method. Starting from the perspective of battery system design, this invention adjusts the types and proportions of the positive and negative active materials, and uses a variety of conductive agents such as carbon nanotubes, carbon fibers, super conductive carbon black, and flake graphite in combination to prepare an energy and power balanced lithium-ion battery. However, the specific energy of this invention is only 180 Wh / kg, far from meeting the requirement of over 300 Wh / kg for current high specific energy lithium-ion batteries. In addition, the overall development cycle of this method is relatively long, the R & D investment is large, and the improvement of the efficiency of the battery power capacity is not obvious. There is still a large gap between the actual performance and the design. Chinese patent document CN108598598 discloses a high specific energy and high power lithium battery and its manufacturing method. This invention designs a composite battery starting from the assembly process. The first battery has a relatively high specific energy and is assembled by the winding process, and the second battery has high power characteristics and is assembled by the stacking process. Then, the two are connected in series or parallel and then subjected to a shaping process, and finally packaged together to form a finished battery, helping the battery to take into account both the high specific energy and high power advantages at the same time. However, the assembly process and implementation method of this invention are complex, the resource and time costs are relatively high, the production line compatibility is small, and at the same time, the improvement of the efficiency of the lithium-ion battery power capacity is limited. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies and defects of the prior art, and to provide a method and device for extending the duration of high-rate discharge of lithium-ion batteries. By externally assisting in adjusting the battery temperature, the efficiency of the battery power capacity is improved, and the duration of high-rate discharge of lithium-ion batteries is effectively extended.

[0007] In the first aspect of the present invention, a method for extending the duration of high-rate discharge of lithium-ion batteries is provided, including the steps of:

[0008] Real-time monitoring of the current state of charge of the lithium-ion battery and the real-time temperature of the lithium-ion battery;

[0009] Comparing the real-time temperature of the lithium-ion battery with the optimal discharge temperature corresponding to the current state of charge of the lithium-ion battery;

[0010] According to the comparison result, cooling, heat preservation or heating is performed on the lithium-ion battery to adjust the temperature of the lithium-ion battery, so that when the lithium-ion battery discharges at the extreme rate under different states of charge, minimum polarization and the longest high-rate continuous discharge time are achieved.

[0011] Among them, if the real-time temperature of the battery > the optimal discharge temperature, the battery is cooled; if the real-time temperature of the battery = the optimal discharge temperature, the battery is heat-preserved; if the real-time temperature of the battery < the optimal discharge temperature, the battery is heated.

[0012] The optimal discharge temperature corresponding to the current state of charge of the battery is obtained according to a state of charge-optimal discharge temperature database, and the state of charge-optimal discharge temperature database stores relationship data of optimal discharge temperatures corresponding to different states of charge.

[0013] Among them, the optimal discharge temperature corresponding to different states of charge is determined by the following method:

[0014] When 100% SOC≥SOC>65% SOC, the optimal discharge temperature T=T 1C +n1(T nlimitC -T 1C );

[0015] When 65% SOC≥SOC>35% SOC, the optimal discharge temperature T=T 1C +n2(T nlimitC -T 1C );

[0016] When 35% SOC≥SOC>0% SOC, the optimal discharge temperature T=T 1C +n3(T nlimitC -T 1C );

[0017] Where, T 1C =f(SOC), which represents the temperature curve under 1C discharge with the state of charge of the lithium-ion battery as the independent variable and the battery body temperature as the dependent variable, T nlimitC =f(SOC), indicating the limit discharge rate n limitC Temperature curve under discharge, with the state of charge of the lithium-ion battery as the independent variable and the battery body temperature as the dependent variable; n1, n2, and n3 are different parameters.

[0018] Among them, the range of parameter n1 is 0-0.5, preferably 0.3; the range of parameter n2 is 0.3-0.7, preferably 0.5; the range of parameter n3 is 0.5-1, preferably 0.67.

[0019] Wherein, the limit discharge rate n limitC Obtained by passing lithium-ion batteries through preset test steps;

[0020] Preset test steps, including:

[0021] Determine the charging and discharging voltage range of the lithium-ion battery, charge it to the rated voltage in a constant current and constant pressure mode in a constant temperature incubator, select the preset current as the cut-off current of the constant voltage section, and obtain a fully charged battery;

[0022] Discharge the fully charged battery at different current rates, record the discharge capacity and battery body temperature, and determine the capacity retention rate at different rates based on the discharge capacity at different current rates;

[0023] Determine the ultimate discharge rate n according to the capacity retention rate at different rates and the temperature at the end of battery discharge. limitC ; Among them, at the ultimate discharge rate n limit The capacity retention rate under C is ≥ the preset capacity retention rate value a, and at the same time, the temperature at the end of battery discharge ≤ the preset temperature value b at the end of battery discharge.

[0024] Among them, the range of the constant charging current value of the constant current and constant voltage charging mode is 0.1C - 2C, preferably 1C, and the range of the cut-off current in the constant voltage section is 0.01C - 0.1C, preferably 0.05C.

[0025] Among them, the range of the preset capacity retention rate value a is 90% - 100%, preferably 95%, and the range of the preset temperature value b at the end of battery discharge is 70°C - 85°C, preferably 75°C.

[0026] Among them, the current range of the current discharge at different rates is 1C - 10C.

[0027] In the second aspect of the present invention, a device for extending the large-rate discharge duration of a lithium-ion battery is provided, including:

[0028] A monitor, including a state of charge monitoring module and a temperature monitoring module, for real-time monitoring of the current state of charge of the lithium-ion battery and the real-time temperature of the lithium-ion battery; a controller, for comparing the real-time temperature of the lithium-ion battery with the optimal discharge temperature corresponding to the current state of charge of the lithium-ion battery; according to the comparison result, cooling, heat preservation or heating the lithium-ion battery is performed to adjust the temperature of the lithium-ion battery, so that when the lithium-ion battery discharges at the ultimate rate in different states of charge, the minimum polarization and the longest large-rate continuous discharge time are achieved.

[0029] The technology of the present invention improves the efficiency of the battery power capacity by externally assisting in adjusting the battery temperature, effectively extends the large-rate discharge duration of the lithium-ion battery, breaks through the bottleneck that it is difficult to have both high specific energy and high power capacity for the lithium-ion battery, and meets the comprehensive performance index requirements of the lithium-ion battery for multiple application scenarios; the present invention uses external assistance to reduce the polarization phenomenon of the high specific energy lithium-ion battery, and directly realizes the use of mature products close to the indicators by improving the efficiency of the battery power capacity. Brief Description of the Drawings

[0030] Figure 1 It is a schematic diagram of the control logic of the controller for temperature control of the present invention;

[0031] Figure 2 It is a confirmation diagram of the ultimate discharge rate of the embodiment of the present invention;

[0032] Figure 3It is the discharge temperature-state of charge curve diagram of Embodiment 1C of the present invention;

[0033] Figure 4 It is the discharge temperature-state of charge curve diagram of the extreme rate 7C discharge of the embodiment of the present invention;

[0034] Figure 5 It is the state of charge-optimal discharge temperature comparison curve diagram of the embodiment of the present invention;

[0035] Figure 6 It is the instantaneous power comparison diagram when the embodiment of the present invention and the comparative example perform 7C pulse discharge at 30% SOC;

[0036] Figure 7 It is the discharge voltage curve comparison diagram when the embodiment of the present invention and the comparative example perform 7C pulse discharge at 30% SOC. Detailed implementation manners

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] Relevant research shows that the duration of high-rate discharge of lithium-ion batteries is shorter than the theoretical time. The essential reason is that the excessive exchange current density leads to an increase in the polarization of lithium-ion batteries under this working condition. One is that the contact resistance of various materials in the battery brings a large side effect of ohmic polarization; the other is that the rate of the reaction of lithium ions gaining electrons is much smaller than the migration rate of electrons under high current, thus generating a large electrochemical polarization; the third is that within a few seconds of starting high-current pulse discharge, lithium ions burst out from the negative electrode and accumulate on the surface of the negative electrode, while in the electrolyte far from the negative electrode, the concentration of lithium ions is very low, thus causing a large concentration polarization. The superposition of the three causes the potential of the positive and negative electrodes in the system to deviate seriously from the equilibrium potential, ultimately resulting in an instant drop of the battery voltage to the cut-off voltage, the end of discharge, but the capacity is not fully discharged, and the efficiency of power capacity utilization is extremely low.

[0039] The inventors of the present application found during the experiment that at the same discharge current, as the temperature increases, the activity of the battery increases, the difference between the polarization potential and the equilibrium potential will decrease, the voltage drop rate slows down, the available capacity value will increase slightly, and at the same time the battery discharge time can be effectively extended.

[0040] Therefore, a method for extending the high-rate discharge duration of lithium-ion batteries according to the present invention is proposed, including the following steps:

[0041] Real-time monitor the current state of charge of the lithium-ion battery and the real-time temperature of the lithium-ion battery;

[0042] Compare the real-time temperature of the lithium-ion battery with the optimal discharge temperature corresponding to the current state of charge of the lithium-ion battery;

[0043] According to the comparison result, cool down, keep warm or heat the lithium-ion battery to adjust the temperature of the lithium-ion battery, so that when the lithium-ion battery discharges at the extreme rate under different states of charge, the minimum polarization and the longest continuous discharge time at the maximum rate are achieved.

[0044] In the embodiment of the present application, if the real-time temperature of the battery > the optimal discharge temperature, the battery is cooled down; if the real-time temperature of the battery = the optimal discharge temperature, the battery is kept warm; if the real-time temperature of the battery < the optimal discharge temperature, the battery is heated; when there is no need to cool down, keep warm or heat the lithium-ion battery, stop the operation of cooling down, keeping warm or heating the lithium-ion battery, and specifically switch among the three battery temperature adjustment modes of cooling down, keeping warm and heating according to the real-time situation.

[0045] In the embodiment of the present application, by simultaneously combining the real-time state of charge of the battery and the real-time change of the temperature of the battery body, continuous judgments are made and new temperature control instructions are issued, thereby realizing the targeted adjustment of the battery temperature, and finally ensuring that no matter what state of charge the battery is in when discharging at the extreme rate, there is the minimum polarization and the longest continuous discharge time, and fully improving the efficiency of the battery power capacity.

[0046] In the embodiment of the present application, the optimal discharge temperature corresponding to the current state of charge of the battery is obtained from the state of charge - optimal discharge temperature database, and the state of charge - optimal discharge temperature database stores the relationship data of the optimal discharge temperature corresponding to different states of charge.

[0047] In the embodiment of the present application, the optimal discharge temperature corresponding to different states of charge is determined by the following method:

[0048] When 100% SOC ≥ state of charge > 65% SOC, the optimal discharge temperature T = T 1C + n1(T nlimitC - T 1C );When 65% SOC ≥ state of charge > 35% SOC, the optimal discharge temperature T = T 1C + n2(T nlimitC - T 1C );When 35% SOC ≥ state of charge > 0% SOC, the optimal discharge temperature T = T 1C + n3(T nlimitC - T 1C );

[0049] In the formula, T 1C = f(SOC), representing the temperature curve with the state of charge of the lithium-ion battery as the independent variable and the temperature of the battery body as the dependent variable under 1C discharge, TnlimitC =f(SOC), indicating the limit discharge rate n limitC Temperature curve under discharge, with the state of charge of the lithium-ion battery as the independent variable and the battery body temperature as the dependent variable; n1, n2, and n3 are different parameters.

[0050] In the embodiment of the present application, the range of parameter n1 is 0-0.5, preferably 0.3; the range of parameter n2 is 0.3-0.7, preferably 0.5; the range of parameter n3 is 0.5-1, preferably 0.67.

[0051] In the embodiment of the present application, the limit discharge rate n limitC Obtained by passing lithium-ion batteries through preset test steps;

[0052] The above-mentioned preset test steps include:

[0053] Determine the charging and discharging voltage range of the lithium-ion battery, charge it to the rated voltage in a constant current and constant pressure mode in a constant temperature incubator, select the preset current as the cut-off current of the constant voltage section, and obtain a fully charged battery;

[0054] Discharge the fully charged battery at different current rates, record the discharge capacity and battery body temperature, and determine the capacity retention rate at different rates based on the discharge capacity at different current rates;

[0055] According to the capacity retention rate at different rates and the temperature at the end of battery discharge, the limit discharge rate nlimitC is determined; wherein, at the limit discharge rate nlimitC limit The capacity retention rate under C is ≥ the preset capacity retention rate value a, and the battery final discharge temperature is ≤ the preset battery final discharge temperature value b.

[0056] The preset capacity retention rate value a and the preset battery end-of-discharge temperature value b are determined based on the customer's demand indicators for the battery and the upper temperature limit of the electrolyte of the system itself.

[0057] The capacity retention rate is the ratio of the discharge capacity at different rates to the discharge capacity at 1C rate.

[0058] In the embodiment of the present application, the charging constant current value of the constant current constant pressure type charging is in the range of 0.1C-2C, preferably 1C, and the cut-off current of the constant voltage section is in the range of 0.01C-0.1C, preferably 0.05C.

[0059] In the embodiment of the present application, the current range of the different rate current discharge is 1C-10C, and the number of selected test currents ranges from 1 to 10, preferably 7 currents in total, namely 1C, 2C, 3C, 4C, 5C, 6C, and 7C.

[0060] In the embodiment of the present application, the range of the preset capacity retention rate value a is 90%-100%, preferably 95%, and the range of the preset end-of-discharge temperature value b of the battery is 70°C-85°C, preferably 75°C.

[0061] In the second aspect of the embodiment of the present invention, there is provided a device for extending the high-rate discharge duration of a lithium-ion battery, including:

[0062] A monitor, including a state-of-charge monitoring module and a temperature monitoring module, for real-time monitoring of the current state of charge of the lithium-ion battery and the real-time temperature of the lithium-ion battery; a controller, for comparing the real-time temperature of the lithium-ion battery with the optimal discharge temperature corresponding to the current state of charge of the lithium-ion battery, and according to the comparison result, cooling, heat preservation or heating the lithium-ion battery to realize the regulation of the temperature of the lithium-ion battery, so that when the lithium-ion battery discharges at the extreme rate under different states of charge, the minimum polarization and the longest high-rate continuous discharge time are achieved.

[0063] In the embodiment of the present application, as Figure 1 shown, the controller of the present invention may include a control unit, a heating unit, a cooling unit and a heat preservation unit. The control unit can real-time monitor the state of charge and temperature level of the battery through the monitor, and according to the control program stored inside, such as the "state of charge - discharge temperature" relationship database described above, and according to the data in this relationship database, immediately output instructions to the heating unit, the cooling unit and the heat preservation unit to control the actions of the heating unit, the cooling unit and the heat preservation unit.

[0064] The heating unit can immediately respond to the instruction of the control unit to start the heating operation or cut off the heating operation. The cooling unit can immediately respond to the instruction of the control unit to start the cooling operation or cut off the cooling operation. The heat preservation unit can immediately respond to the instruction of the control unit to start the heat preservation operation or cut off the heat preservation operation.

[0065] In the present application, the cooling unit is a fan or a liquid cooling plate module attached to the battery. The heating unit is a heating film attached to the surface of the battery. The heat preservation unit is a heating film or heating wire attached to the surface of the battery.

[0066] Example:

[0067] A ternary soft-pack battery with an energy density of 340 Wh / kg and a capacity of 9.2 AH is selected as the test object.

[0068] First, determine the extreme discharge rate n of the battery in this system limit C.

[0069] According to the product specification of the battery in this system, determine that its normal charge and discharge voltage range is 2.5 - 4.25V. Adjust the temperature of the incubator to 25°C for subsequent tests, and paste a high-precision temperature-sensing wire on the battery body to collect the temperature change during the process.

[0070] Charge and discharge mode: First, charge at a constant current of 1C until it reaches 4.25V and then switch to constant voltage charging. Stop charging when the current decreases to 0.05C; let it stand for 30 minutes; discharge at currents of 1C, 2C, 3C, 4C, 5C, 6C, and 7C respectively, with the cut-off voltage being 2.5V.

[0071] Data processing: Based on the discharge capacity at 1C, calculate the capacity retention rates at different discharge rates respectively. At the same time, it is necessary to screen out the highest temperature of the battery body at the end of discharge at different rates.

[0072] The test results are as Figure 2 shown. The capacity retention rates of 1C, 2C, 3C, 4C, 5C, 6C, and 7C are 100%, 98.12%, 96.67%, 96.51%, 96.08%, 96.01%, and 95.97% respectively, and the highest temperatures of the battery body are 32.0°C, 37.1°C, 42.6°C, 47.7°C, 53.0°C, 62.6°C, and 72.0°C respectively.

[0073] Comprehensive judgment criterion: When the capacity retention rate ≥ 95% and the battery temperature at the end of discharge ≤ 75°C, 7C is considered the limit discharge rate of this system.

[0074] Secondly, process the discharge data to obtain the corresponding "state of charge - optimal discharge temperature" database.

[0075] Process the 1C and 7C discharge data measured in the above steps. Taking the state of charge SOC of the battery as the independent variable and the corresponding temperature T of the battery body as the dependent variable, two temperature curves T 1C = f(SOC) are obtained, as Figure 3 shown, and T 7C = f(SOC), as Figure 4 shown. Calculate the optimal discharge temperature T according to the following formula:

[0076] ① When 100% SOC ≥ state of charge > 65% SOC: T = T 1C + 0.33(T nlimitC - T 1C );

[0077] ② When 65% SOC ≥ state of charge > 35% SOC: T = T 1C + 0.5(T nlimitC - T 1C );

[0078] ③ When 35% SOC ≥ state of charge > 0% SOC: T = T 1C + 0.67(T nlimitC - T 1C ).

[0079] The state of charge - optimal temperature (T) fitting curve is obtained, as shown in Figure 5 shown, and the corresponding "state of charge - optimal discharge temperature" database is generated.

[0080] Finally, the above - mentioned "state of charge - optimal discharge temperature" database is embedded into the control unit of the intelligent temperature regulation module, and the 7C discharge duration, instantaneous discharge power curve, and discharge voltage curve of the battery with a state of charge of 30% SOC in this system are tested to verify its effectiveness.

[0081] Comparative example:

[0082] The test battery cells of the comparative example and the example are of the same system and the same batch. The difference is that the above - mentioned temperature control technology is not used for temperature control of the battery.

[0083] The test results of the instantaneous power are as shown in Figure 6 shown. In the example, when discharging at a 7C current with a state of charge of 30% SOC, the discharge duration reaches 39.60 s, and the initial discharge power reaches 182.3 W. In the comparative example, the discharge duration is only 12.42 s, and the initial discharge power is 178.4 W. Moreover, the instantaneous power in the example is higher than that in the comparative example throughout the discharge process.

[0084] After using the above - mentioned temperature control technology for temperature control of the battery, the growth rate of the 7C discharge duration of the battery of the same system reaches 218.9%; in addition, as can be seen from Figure 7 , the polarization voltage (ΔU 实施例 = 0.48 V) of the example is 9.43% lower than that of the comparative example (ΔU 对比例 = 0.53 V).

[0085] The test results show that the method of the present application can effectively reduce the polarization phenomenon of high - specific - energy lithium - ion batteries, reduce the difference between the polarization potential and the equilibrium potential, further improve the efficiency of the battery power capacity, extend the discharge duration at the extreme rate, so as to assist lithium - ion batteries to meet the comprehensive performance index requirements of lithium - ion batteries in multiple application scenarios.

[0086] The foregoing has shown and described the basic principles, main features and advantages of the present invention. For a person skilled in the art, it is obvious that the present invention is not limited to the details of the above-mentioned exemplary embodiments, and without departing from the spirit or basic features of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to embrace all changes that fall within the meaning and scope of the equivalent elements of the claims in the present invention.

[0087] In addition, it should be understood that although this specification is described according to the embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for extending the duration of high-rate discharge of a lithium-ion battery, characterized in that, Including the steps: Real-time monitor the current state of charge (SOC) of the lithium-ion battery and the real-time temperature of the lithium-ion battery; Compare the real-time temperature of the lithium-ion battery with the optimal discharge temperature corresponding to the current state of charge of the lithium-ion battery; According to the comparison result, cool down, keep warm or heat the lithium-ion battery to adjust the temperature of the lithium-ion battery, so that when the lithium-ion battery discharges at the extreme rate under different states of charge, the minimum polarization and the longest continuous discharge time at the maximum rate can be achieved.

2. The method for extending the high-rate discharge duration of a lithium-ion battery according to claim 1, wherein If the real-time temperature of the battery > the optimal discharge temperature, cool down the battery; if the real-time temperature of the battery = the optimal discharge temperature, keep the battery warm; if the real-time temperature of the battery < the optimal discharge temperature, heat the battery.

3. The method for extending the high-rate discharge duration of a lithium-ion battery according to claim 1, wherein The optimal discharge temperature corresponding to the current state of charge of the battery is obtained from the database of state of charge - optimal discharge temperature, and the database of state of charge - optimal discharge temperature stores the relational data of the optimal discharge temperature corresponding to different states of charge.

4. The method for prolonging the high-rate discharge duration of a lithium-ion battery according to claim 3, wherein The optimal discharge temperature corresponding to different states of charge is determined by the following method: When 100% SOC ≥ state of charge > 65% SOC, the optimal discharge temperature T = T 1C + n1(T nlimitC - T 1C ); When 65% SOC ≥ state of charge > 35% SOC, the optimal discharge temperature T = T 1C +n2(T nlimitC -T 1C ); When 35% SOC ≥ state of charge > 0% SOC, the optimal discharge temperature T = T 1C +n3(T nlimitC -T 1C ); Wherein, T 1C = f(SOC) represents a temperature curve with the state of charge (SOC) of the lithium-ion battery as the independent variable and the temperature of the battery body as the dependent variable under 1C discharge, and T nlimitC = f(SOC) represents the limiting discharge rate n limit C discharge, with the state of charge (SOC) of the lithium-ion battery as the independent variable and the temperature of the battery body as the dependent variable; n 1， n 2， n3 are different parameters.

5. The method for prolonging the high-rate discharge duration of a lithium-ion battery according to claim 4, wherein The range of parameter n1 is 0 - 0.5, preferably 0.3; the range of parameter n2 is 0.3 - 0.7, preferably 0.5; the range of parameter n3 is 0.5 - 1, preferably 0.

67.

6. The method for prolonging the high-rate discharge duration of a lithium-ion battery according to claim 1, wherein The limit discharge rate n limit C is obtained by subjecting the lithium-ion battery to a preset test procedure; Preset the test steps, including: Determine the charge-discharge voltage range of the lithium-ion battery, charge it to the rated voltage in a constant-temperature incubator with constant current and constant voltage mode, select the preset current as the cut-off current in the constant voltage stage to obtain a fully charged battery; Discharge the fully charged battery at different rate currents, record the discharge capacity and the temperature of the battery body, and determine the capacity retention rate at different rates based on the discharge capacity at different rates; Determine the ultimate discharge rate n based on the capacity retention rate at different magnification rates and the temperature at the end of battery discharge limit C; Among them, at the limit discharge rate n limit C, the capacity retention rate ≥ the preset capacity retention rate value a, and at the same time, the temperature at the end of battery discharge ≤ the preset temperature value b at the end of battery discharge.

7. The method for prolonging the high-rate discharge duration of a lithium-ion battery according to claim 6, wherein The range of the constant charging current value in the constant current and constant voltage charging mode is 0.1C - 2C, preferably 1C, and the range of the cut-off current in the constant voltage stage is 0.01C - 0.1C, preferably 0.05C.

8. The method for extending the high-rate discharge duration of a lithium-ion battery according to claim 6, characterized in that, The range of the preset capacity retention rate value a is 90% - 100%, preferably 95%, and the range of the preset battery discharge end temperature value b is 70°C - 85°C, preferably 75°C.

9. The method for prolonging the high-rate discharge duration of a lithium-ion battery according to claim 6, wherein The current range of the different rate current discharges is 1C - 10C.

10. A device for extending the duration of high-rate discharge of a lithium-ion battery, characterized in that, Including: A monitor, including a state of charge monitoring module and a temperature monitoring module, for real-time monitoring the current state of charge of the lithium-ion battery and the real-time temperature of the lithium-ion battery; A controller, for comparing the real-time temperature of the lithium-ion battery with the optimal discharge temperature corresponding to the current state of charge of the lithium-ion battery; according to the comparison result, cool down, keep warm or heat the lithium-ion battery to adjust the temperature of the lithium-ion battery, so that when the lithium-ion battery discharges at the extreme rate under different states of charge, the minimum polarization and the longest continuous discharge time at the maximum rate can be achieved.

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