A method for selecting charging conditions of lithium-ion batteries

Abstract

The present invention relates to a method for selecting a charging condition for a lithium-ion battery, comprising the following steps: setting a charging target for the lithium-ion battery so that the charging target is consistent when selecting the charging condition; the charging target includes at least the following information: a starting SOC value, an expected charging time, and a target SOC value; obtaining a preset charging condition; the preset charging condition is at least two; when the charging target is consistent, the corresponding preset charging condition is selected according to different user needs; the selection is made based on test data of a cyclic charging experiment. The present invention, under the premise of consistent charging targets, conducts relevant research on preset charging conditions, takes into account the differences in the decay characteristics of different conditions, and the mainstream BMS embedded in a single condition, optimizes the selection of charging conditions for different user needs, which is crucial to meeting user needs, improving charging efficiency, and delaying battery decay.

Description

Technical Field

[0001] The invention relates to the field of battery management of new energy vehicles, and in particular to a method for selecting a charging condition for a lithium-ion battery. Background Art

[0002] In recent years, as environmental issues have become increasingly prominent, renewable energy has received more and more attention. Among them, lithium-ion batteries have become the preferred power source for major automakers due to their superior comprehensive performance and are widely used in the field of electric vehicles. Reasonable battery management, especially choosing the right method to charge the battery, is crucial to meeting user needs and maintaining battery performance.

[0003] Currently, common lithium-ion battery charging methods mainly include constant current and constant voltage charging, constant power and constant voltage charging, multi-stage current charging, pulse charging, and variable current charging.

[0004] Constant current and constant voltage charging is the main way to charge power batteries at present. It is simple to operate and easy to control, but it cannot eliminate the polarization phenomenon caused by the battery charging process, which affects the charging effect of the battery.

[0005] Constant power charging can improve the charging efficiency of the battery due to the large initial charging current;

[0006] Multi-stage constant current charging can adjust the current level during the charging process to extend the battery life while reducing charging time;

[0007] The purpose of pulse charging is to reduce polarization, increase charging and discharging power, and shorten the battery charging time;

[0008] Variable current charging is a method of calculating the optimized charging current of a power battery using an equivalent circuit model or electrochemical mechanism model of the battery.

[0009] At present, the mainstream battery management system (BMS) is embedded in a single working condition, and does not consider the actual needs of different users to optimize the selection of charging conditions. Therefore, it is of great significance to reasonably select charging conditions considering the requirements such as charging starting point, waiting time and target charging capacity.

[0010] The information disclosed in this background technology section is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art already known to those skilled in the art. Summary of the invention

[0011] In view of the defects existing in the prior art, the purpose of the present invention is to provide a method for selecting charging conditions for lithium-ion batteries. Under the premise of consistent charging goals, relevant research is carried out on preset charging conditions. Considering the differences in the decay characteristics of different conditions and the single working condition embedded in the mainstream BMS, it is crucial to optimize the selection of charging conditions according to different user needs in order to meet user needs, improve charging efficiency and delay battery decay.

[0012] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0013] A method for selecting a charging condition for a lithium-ion battery, characterized in that it comprises the following steps:

[0014] By setting the charging target of the lithium-ion battery, the charging target is made consistent when the charging condition is selected; the charging target includes at least the following information: starting SOC value, expected charging time, and target SOC value;

[0015] Obtaining preset charging conditions; the preset charging conditions are at least two;

[0016] When the charging target is the same, select the corresponding preset charging condition according to different user needs;

[0017] The selection was made based on cyclic charging experimental test data.

[0018] On the basis of the above technical solution, the corresponding preset charging conditions are selected according to different user needs, specifically including:

[0019] According to the different starting SOC points of the battery and the user's expected charging time, select the charging condition with the maximum expected charging capacity of the battery;

[0020] According to the different SOC interval characteristics of the battery, the SOC interval of the battery is divided, and the charging condition with the fastest expected charging time of the battery in the same SOC interval is selected;

[0021] According to the different SOC interval characteristics of the battery, the SOC interval of the battery is divided, and the charging condition with the maximum expected charging energy of the battery in the same SOC interval is selected;

[0022] According to the performance degradation caused by the battery cycle charging experiment, regardless of the battery's starting SOC point and the user's expected charging time, the charging condition with the slowest expected battery capacity degradation is selected;

[0023] According to the performance degradation caused by the battery's cycle charging experiment, without considering the battery's starting SOC point and the user's expected charging time, the charging condition with the highest expected charging energy efficiency of the battery is selected.

[0024] On the basis of the above technical solution, the steps for acquiring the test data of the cyclic charging experiment are as follows:

[0025] Set the number of cycle charging experiments; the default is 1000 times;

[0026] Set the starting SOC value to 0%-80%, with each 20% increase as one SOC interval;

[0027] Set the expected charging time to 5min-30min, with each 5min increment as a test point;

[0028] The test data obtained under different SOC ranges and different test points under different charging conditions;

[0029] The test data includes:

[0030] Charging capacity refers to the amount of electricity that the battery can store, measured in ampere-hours (Ah) or milliampere-hours (mAh);

[0031] Charging time refers to the time required for the battery to charge to the charging cut-off voltage within the same SOC range;

[0032] Charging energy refers to the energy stored in the battery, and the unit of energy is watt-hour (Wh).

[0033] Based on the above technical solution, the default preset charging conditions include: constant current charging condition, constant power charging condition, five-stage constant current charging condition, variable current intermittent charging condition, and composite charging condition combining constant current and constant dQ / dV.

[0034] On the basis of the above technical solution, the charging cut-off voltage is determined according to the provisions of the battery manual;

[0035] The constant current charging condition is 1.6C constant current charging to the charging cut-off voltage;

[0036] The constant power charging condition is 20W constant power charging to the charging cut-off voltage;

[0037] The five-stage constant current charging condition is firstly 2C, 1.8C, 1.6C, 1.4C constant current charging for 5 minutes respectively, and then 1.2C constant current charging to the charging cut-off voltage;

[0038] The variable current intermittent charging condition is firstly to charge at a constant current of 2.5C to a first SOC value, which is 10% by default, and then to stand for a preset intermittent time, which is 2min30s by default, and then to charge at a constant current of 1.92C to a second SOC value, which is 60% by default, and then to stand for a preset intermittent time, and finally to charge at a constant current of 1.34C to a charging cut-off voltage;

[0039] The composite charging condition is to first charge at a constant current of 1C to a third SOC value, where the third SOC value is 20% by default, and then charge at a constant dQ / dV=25Ah / V to a charging cut-off voltage.

[0040] On the basis of the above technical solution, the lithium-ion battery is a battery used in electric vehicles, specifically, any one of the following: a lithium manganese oxide power battery, a lithium iron phosphate power battery, and a ternary material power battery.

[0041] Based on the above technical solution, the default starting SOC value is 0%;

[0042] The default expected charging time is 30 minutes;

[0043] The default target SOC value is 80%.

[0044] The method for selecting a charging condition for a lithium-ion battery described in the present invention has the following beneficial effects:

[0045] On the premise of consistent charging goals, relevant research is carried out on the preset charging conditions. Taking into account the differences in the degradation characteristics of different conditions and the single working conditions embedded in the mainstream BMS, optimizing the selection of charging conditions for different user needs is crucial to meeting user needs, improving charging efficiency and delaying battery degradation. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The present invention has the following accompanying drawings:

[0047] The accompanying drawings are used to better understand the present invention and do not constitute an improper limitation of the present invention.

[0048] Figure 1 A flow chart of a method for selecting a charging condition for a lithium-ion battery according to the present invention.

[0049] Figure 2 The initial charging SOC of the lithium-ion battery is 0%, and the charging capacity of the battery changes at different charging times under different charging conditions.

[0050] Figure 3 The initial charging SOC of the lithium-ion battery is 20%, and the charging capacity change curve of the battery under different charging conditions and different charging times.

[0051] Figure 4 Battery charging time diagram of lithium-ion battery in 20% SOC range under different charging conditions.

[0052] Figure 5 Battery charging energy change curve in the 20% SOC range under five charging conditions of lithium-ion batteries.

[0053] Figure 6 Battery capacity decay curves of lithium-ion batteries under different charging conditions and different decay stages.

[0054] Figure 7 The battery charging energy efficiency change curve under different charging conditions and different degradation stages of lithium-ion batteries. DETAILED DESCRIPTION

[0055] The present invention is further described in detail below in conjunction with the accompanying drawings. The detailed description is an explanation made in conjunction with the exemplary embodiments of the present invention, including various details of the embodiments of the present invention to facilitate understanding, which should be considered as merely exemplary. Therefore, it should be recognized by those skilled in the art that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention. Similarly, for the sake of clarity and conciseness, the description of well-known functions and structures is omitted in the following description.

[0056] The present invention discloses a method for selecting a charging condition for a lithium-ion battery, wherein the lithium-ion battery is a battery used in an electric vehicle, specifically, any one of the following: a lithium manganese oxide power battery, a lithium iron phosphate power battery, and a ternary material power battery.

[0057] The following specific embodiments are described using a company's lithium iron phosphate power battery as an example.

[0058] The charging target of lithium-ion batteries is set as the starting SOC=0%, and the default charging target of the battery is reached within the default expected charging time of 30 minutes, that is, 80% of the rated capacity of the battery is fully charged. According to this charging target, the default preset charging conditions are determined, which are constant current charging condition, constant power charging condition, five-stage constant current charging condition, variable current intermittent charging condition, constant current and constant d Q / d V The average charging current rate of the five combined charging conditions is 1.6C, and the experimental object is a 3.6Ah 26650 lithium iron phosphate battery.

[0059] The constant current charging condition is 1.6C constant current charging to the battery charging cut-off voltage of 3.65V; the constant power charging condition is 20W constant power charging to the battery charging cut-off voltage of 3.65V; the five-stage constant current charging condition is 2C, 1.8C, 1.6C, 1.4C constant current charging for 5 minutes respectively, and 1.2C constant current charging to the battery charging cut-off voltage of 3.65V; the variable current intermittent charging condition is first 2.5C constant current charging to the first SOC value, the SOC value defaults to 10%, Then let it stand for a preset intermittent time, the default intermittent time is 2min30s, and then charge at a constant current of 1.92C to a second SOC value, the default of which is 60%, then let it stand for a preset intermittent time, and finally charge at a constant current of 1.34C to a charging cut-off voltage of 3.65V; the composite charging condition is to first charge at a constant current of 1C to a third SOC value, the default of which is 20%, and then charge at a constant dQ / dV=25Ah / V to a charging cut-off voltage of 3.65V.

[0060] The initial charging SOC of the lithium-ion battery is 0%. The charging capacity change curve of the battery under different charging conditions and different charging times is as follows Figure 2 As shown, it can be found that the charging capacity of the five-stage constant current charging condition within the first 15 minutes is the largest. When charging for 20 minutes, the charging capacity of the five-stage constant current charging and the variable current intermittent charging is not much different. These two conditions are the optimal conditions at this time. When the charging time is 25 minutes, the charging capacity of the variable current intermittent charging is the largest, which is the optimal condition at this time.

[0061] The initial charging SOC of the lithium-ion battery is 20%. The charging capacity change curve of the battery under different charging conditions and different charging times is as follows Figure 3 As shown in the figure, the comparative analysis shows that when the charging time is 15 minutes or less, the variable current intermittent charging condition has the largest charging capacity, and this charging condition is the optimal condition. When the charging time is 20 minutes, from the perspective of capacity, the optimal charging conditions are the five-stage constant current charging condition and the variable current intermittent charging condition.

[0062] Figure 4 This is a graph showing the changes in battery charging time in the 20% SOC range for lithium-ion batteries under different charging conditions. It can be found that if only the speed of charging time is considered, five-stage constant current charging should be used in the 0-20% SOC range, variable current intermittent charging conditions should be used in the 20-40% SOC range, variable current intermittent charging should be used in the 40-60% SOC range, and constant current, constant power or compound charging conditions should be used for 60%-80% SOC.

[0063] Figure 5The figure shows the battery charging energy change curve of the lithium-ion battery in the 20% SOC range under five charging conditions. It is found that the charging energy of the composite charging condition is smaller in the 0-20% SOC range, and the charging energy in other SOC ranges is the largest. That is to say, under the premise of charging the same capacity of the battery, this charging condition has the longest driving range, followed by the variable current intermittent charging condition, and the charging energy of the other three charging conditions is not much different.

[0064] The battery capacity decay curves at different decay stages under different charging conditions of lithium-ion batteries are as follows: Figure 6 As shown, it can be found that in the battery charging cycle, the capacity retention rate of the composite charging condition is the highest and the capacity decay rate is the slowest. After 1000 charging cycles, it decays by 8.996%, and the capacity retention rate of the battery is 91.004%. The capacity of the battery at this time is 3.39Ah; the fastest decay rate is the variable current intermittent charging condition, which decays by 10.125% after 1000 cycles, and the capacity retention rate is 89.875%. The difference between the composite charging condition with the slowest capacity decay rate and the intermittent charging condition with the fastest capacity decay rate is 1.129%.

[0065] Figure 7 The following are the curves of battery charging energy efficiency changes under different charging conditions and different decay stages of lithium-ion batteries. It can be found that the energy efficiency of variable current intermittent charging is the lowest, which is 94.14% after 1000 cycles. After 1000 aging cycles, the energy utilization efficiency is the highest under the 2#CP condition, which is 95.855%, with a difference of 1.715%. The possible reason is that the initial charging current of the 4# variable current intermittent charging condition is the largest, reaching 2.5C (9A), and the internal resistance of the battery is large at the low end SOC. As the battery ages, the internal resistance of the battery will gradually increase, resulting in increased battery energy consumption and reduced charging energy efficiency.

[0066] Obviously, the above-mentioned implementation cases of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

[0067] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A method for selecting a charging condition for a lithium-ion battery, characterized in that: The steps include: By setting the charging target of the lithium-ion battery, the charging target is made consistent when the charging condition is selected; the charging target includes at least the following information: starting SOC value, expected charging time, and target SOC value; Obtain preset charging conditions; The preset charging conditions include at least two types; When the charging target is the same, select the corresponding preset charging condition according to different user needs; The selection is made based on the test data of the cycle charging experiment; The method of selecting corresponding preset charging conditions according to different user needs specifically includes: According to the different starting SOC points of the battery and the user's expected charging time, select the charging condition with the maximum expected charging capacity of the battery; According to the different SOC interval characteristics of the battery, the SOC interval of the battery is divided, and the charging condition with the fastest expected charging time of the battery in the same SOC interval is selected; According to the different SOC interval characteristics of the battery, the SOC interval of the battery is divided, and the charging condition with the maximum expected charging energy of the battery in the same SOC interval is selected; According to the performance degradation caused by the battery cycle charging experiment, regardless of the battery's starting SOC point and the user's expected charging time, the charging condition with the slowest expected battery capacity degradation is selected; According to the performance degradation caused by the battery cycle charging experiment, without considering the battery's starting SOC point and the user's expected charging time, the charging condition with the highest expected charging energy efficiency of the battery is selected; The steps for obtaining the test data of the cyclic charging experiment are as follows: Set the number of cycle charging experiments; the default is 1000 times; Set the starting SOC value to 0%-80%, with each 20% increase as one SOC interval; Set the expected charging time to 5min-30min, with each 5min increment as a test point; The test data obtained under different SOC ranges and different test points under different charging conditions; The test data includes: Charging capacity refers to the amount of electricity that the battery can store, measured in ampere-hours (Ah) or milliampere-hours (mAh); Charging time refers to the time required for the battery to charge to the charging cut-off voltage within the same SOC range; Charging energy refers to the energy stored in the battery, and the unit of energy is watt-hour (Wh); The default preset charging conditions include: constant current charging condition, constant power charging condition, five-stage constant current charging condition, variable current intermittent charging condition, and composite charging condition combining constant current and constant dQ / dV; Determine the charging cut-off voltage according to the regulations in the battery manual; The constant current charging condition is 1.6C constant current charging to the charging cut-off voltage; The constant power charging condition is 20W constant power charging to the charging cut-off voltage; The five-stage constant current charging condition is firstly 2C, 1.8C, 1.6C, 1.4C constant current charging for 5 minutes respectively, and then 1.2C constant current charging to the charging cut-off voltage; The variable current intermittent charging condition is firstly to charge at a constant current of 2.5C to a first SOC value, which is 10% by default, and then to stand for a preset intermittent time, which is 2min30s by default, and then to charge at a constant current of 1.92C to a second SOC value, which is 60% by default, and then to stand for a preset intermittent time, and finally to charge at a constant current of 1.34C to a charging cut-off voltage; The composite charging condition is to first charge at a constant current of 1C to a third SOC value, where the third SOC value is 20% by default, and then charge at a constant dQ / dV=25Ah / V to a charging cut-off voltage.

2. A method for selecting a charging condition for a lithium-ion battery as claimed in claim 1, characterized in that: The lithium-ion battery is a battery used in electric vehicles, specifically, any one of the following: a lithium manganese oxide power battery, a lithium iron phosphate power battery, and a ternary material power battery.

3. A method for selecting a charging condition for a lithium-ion battery as claimed in claim 1, characterized in that: The default starting SOC value is 0%; The default expected charging time is 30 minutes; The default target SOC value is 80%.

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