CN116111219B - Method for quickly charging battery without lithium precipitation - Google Patents

Abstract

The invention discloses a battery lithium-precipitation-free quick charging method, which comprises the following steps: establishing an electrochemical-thermal coupling heterogeneous model of the battery to be tested; based on the electrochemical-thermal coupling heterogeneous model, performing simulated charging at least two test temperatures to obtain first charging data when a plurality of set charge states trigger lithium precipitation respectively at each test temperature; acquiring second charging data corresponding to the first charging data by using a three-electrode test method; matching the corresponding first charging data with the corresponding second charging data to obtain a target model; and acquiring a maximum charging current MAP without lithium precipitation based on the target model, and determining a quick charging method without lithium precipitation of the battery. By using this method, the charging current can be adjusted according to the change in temperature and state of charge, and the battery can be rapidly charged while being kept close to the boundary current and smaller than the boundary current.

Description

Method for quickly charging battery without lithium precipitation

Technical Field

The invention relates to the field of lithium batteries, in particular to a battery lithium-ion-free quick-charging method.

Background

The application of the lithium ion battery in the pure electric vehicle is more and more extensive, but compared with the traditional fuel vehicle, the problems of mileage anxiety, long charging time and the like become the main problems of hindering the development of the electric vehicle. Therefore, the improvement of the quick charge capability becomes a main development direction of battery manufacturers and whole factories. The existing quick charging method shortens the charging time mainly by adjusting the charging multiplying power. The low-temperature and high-rate charging can cause lithium precipitation of the battery, and further cause accelerated decay of the capacity, output power and other performances of the battery. And, a large amount of heat generated during the fast charge of the battery is difficult to uniformly and effectively dissipate, and also causes accelerated decay and other safety problems.

The invention patent CN112054568A discloses a rapid charging method, which obtains an optimal charging curve by determining the maximum charging multiplying power of a battery under different SOC, and ensures that the charging current is as close to the optimal charging curve as possible so as to ensure that lithium precipitation does not occur during battery charging and the service life of the battery is not damaged. However, temperature considerations are not considered in this approach. When the method is used for determining the quick charging strategy, the quick charging strategy needs to be tested under each use environment, the workload is large, and the testing cost is high.

Disclosure of Invention

In order to overcome the defects in the prior art, the embodiment of the invention provides a battery lithium-precipitation-free quick charging method, by using the method, the charging current can be adjusted according to the change of temperature and charge state, and the battery can be charged by using the maximum charging current under the state of no lithium precipitation, so that the battery can be quickly charged under the condition of not damaging the service life of the battery.

In order to achieve the above purpose, the invention adopts the following technical scheme: a battery lithium-ion-free quick charge method comprises the following steps:

establishing an electrochemical-thermal coupling heterogeneous model of the battery to be tested;

based on the electrochemical-thermal coupling heterogeneous model, performing simulated charging at least two test temperatures to obtain first charging data when a plurality of set charge states trigger lithium precipitation respectively at each test temperature;

acquiring second charging data corresponding to the first charging data by using a three-electrode test method;

matching the corresponding first charging data with the corresponding second charging data to obtain a target model;

and acquiring a maximum charging current MAP without lithium precipitation based on the target model, and determining a quick charging method without lithium precipitation of the battery.

The target model is obtained, and the trigger lithium-precipitation current curve at any temperature can be predicted by using the target model, so that in the charging process, the charging current can be adjusted according to the change of the temperature and the charge state, the charging current is as close to the boundary current as possible but smaller than the boundary current, the battery is ensured to be charged with the maximum charging current in the safe lithium-precipitation boundary, and the battery is rapidly charged without lithium precipitation.

In the method, multiple groups of charging data under different test temperatures are utilized for calibration, the model is subjected to parameter identification, a target model about lithium precipitation of the battery is obtained, the target model is ensured to meet the precision requirement in the temperature test range, the process does not need to perform the test under the full temperature, the test times are reduced, and the test cost is reduced.

The electrochemical-thermal coupling heterogeneous model for lithium analysis of the battery to be tested comprises an electrochemical model, a thermal model and a lithium analysis model. For a person skilled in the art, the above model can be built up using existing relations for the purposes of this application. For example, an electrochemical model is established according to a liquid phase substance conservation equation, a solid phase substance conservation equation, a liquid phase charge conservation equation, a solid phase charge conservation equation, a charge conservation equation, an electrode reaction dynamics equation and the like. And building a thermal model according to an energy conservation equation. And establishing a lithium analysis model according to a lithium analysis reaction kinetic equation.

The specific process for acquiring the first charging data comprises the following steps: and (3) at a preset test temperature, performing simulated charging by using an electrochemical-thermal coupling heterogeneous model, so that lithium precipitation is triggered when the state of charge is set, and obtaining a voltage time-varying curve in the simulated charging process, namely voltage-time data. Specifically, if the first current is used for charging from 0% to 10% of SOC and the second current is used for charging from 10% to 20% of SOC and triggering lithium precipitation, the charging current is sequentially changed to trigger lithium precipitation at each set state of charge, and a full battery voltage time-varying curve (full battery voltage-time data) and a negative electrode voltage time-varying curve (negative electrode voltage-time data) in the simulation charging process are obtained. Otherwise, the charging current is adjusted, and the simulation charging is carried out again.

Taking a lithium iron phosphate battery as an example, the step of acquiring second charging data by a three-electrode test method is described as follows: at a preset test temperature, respectively connecting the positive electrode and the negative electrode of the battery by using a new Wei charge-discharge device, and connecting the negative electrode-reference electrode and the positive-negative electrode full battery by using a tester (HIOKI); charging the battery to 3.65V at constant current and constant voltage of 0.33C, discharging to 2.5V at constant current of 0.33C, and circulating for 3 times; and charging to 3.65V by using a test current, and monitoring the negative electrode-reference electrode potential and the positive-negative electrode full battery voltage by using a synchronous tester (HIOKI) to obtain negative electrode voltage-time data and full battery voltage-time data.

And the maximum charging current MAP without lithium precipitation is corresponding to boundary current when lithium precipitation is triggered by different charge states under different temperatures.

When the trigger is used for lithium precipitation, the state is that the potential of the negative electrode is just equal to 0, and the corresponding current in the state is boundary current.

Further, based on the electrochemical-thermal coupling heterogeneous model, performing simulated charging at least two test temperatures to obtain first charging data when a plurality of set charge states trigger lithium precipitation respectively at each test temperature, including:

selecting at least three temperatures as test temperatures in a temperature test range;

selecting a plurality of charge states from 0% SOC to 100% SOC as set charge states;

based on the electrochemical-thermal coupling heterogeneous model, simulation charging is sequentially carried out from 0% SOC to 100% SOC at a plurality of test temperatures, and when the simulation charging reaches each set charge state, the potential of the negative electrode is equal to zero, so that first charging data of the simulation charging are obtained.

Further, two boundary temperatures within the temperature test range and at least one internal temperature located between the two boundary temperatures are taken as test temperatures. In practical application, the temperature of-20-45 ℃ is generally selected as the temperature test range. The lowest temperature and the highest temperature in the temperature test range are taken as boundary temperatures, and any temperature between the lowest temperature and the highest temperature is taken as an internal temperature. The temperature test range is set at-20 ℃ to 45 ℃ so that the battery can meet the low-temperature environment and the high-temperature environment which can be possibly achieved in life, and the evaluation of the battery is more reliable. In particular, the internal temperature may be chosen to be the intermediate temperature between the two boundary temperatures and several more specific temperatures, such as 0 ℃, 25 ℃. Preferably, four test temperatures including two boundary temperatures may be selected.

Further, a plurality of states of charge are selected from the 0% soc to 100% soc at regular intervals as the set states of charge. And determining the size of the interval according to the accuracy requirement on the target model, and controlling the quantity of the set charge states. Under the condition of higher requirement on the accuracy of the target model, the number of the set charge states is increased. In contrast, in the case where the accuracy requirement on the target model is low, the number of set states of charge is reduced.

Further, the charging data includes at least full battery voltage-time data. The application is to test the time-varying data of the full battery voltage during the charging process. And comparing the full battery voltage-time data obtained in the simulated charging with corresponding full battery voltage-time data obtained in the three-electrode test, thereby being used for identifying parameters of the model.

Further preferably, the charging data further includes at least one of negative voltage-time data or positive voltage-time data. Namely, data of the change of the negative electrode voltage or the positive electrode voltage with time during the charging process is tested. For each test temperature, a plurality of data can be used for calibration, so that the credibility of the model is improved.

Further, the acquiring the second charging data corresponding to the first charging data by using a three-electrode test method includes:

charging the battery to be tested from 0% SOC to 100% SOC at the same test temperature as the simulated charging;

and acquiring second charging data corresponding to the triggering and lithium precipitation of the first charging data under the same temperature and the same charge state by a three-electrode test method.

Further, the corresponding first charging data and second charging data are compared, and a target model is obtained, including:

respectively comparing the corresponding first charging data with the corresponding second charging data at each test temperature; and when the alignment error is larger than the preset error, carrying out parameter identification on the electrochemical-thermal coupling heterogeneous model until the alignment error is smaller than or equal to the preset error at each test temperature, and obtaining a target model.

Further preferably, the corresponding first charging data and second charging data are compared with each other at each test temperature; when the alignment error is larger than the preset error, carrying out parameter identification on the electrochemical-thermal coupling heterogeneous model until the alignment error is smaller than or equal to the preset error at each test temperature, and obtaining a target model, wherein the method comprises the following steps:

calculating RMSE from the first charge data and the second charge data corresponding to the test temperature;

comparing the calculated RMSE with a preset error, and when the RMSE is larger than the preset error, adjusting the dynamic parameters of the electrochemical-thermal coupling heterogeneous model to acquire first charging data at each test temperature again;

repeating the steps until the RMSE calculated at each test temperature is less than or equal to a preset error, and obtaining a target model.

The preset error is set according to the accuracy requirement of the target model. If the preset error is set to be 5%, and when the standard error is less than or equal to 5%, the corresponding electrochemical-thermal coupling heterogeneous model can be regarded as a target model.

Further, the kinetic parameters include solid phase diffusion coefficient, liquid phase diffusion coefficient, reaction rate constant, ion conductivity. The dynamic parameters in the electrochemical-thermal coupling heterogeneous model all meet the Arrhenius equation in temperature. Therefore, by fitting the charging data at a plurality of test temperatures, the activation energy of dynamic parameters such as solid phase diffusion coefficient, liquid phase diffusion coefficient, reaction rate constant, ion conductivity and the like can be verified, so that the target model meets the precision requirement at all temperatures.

Further, based on the target model, obtaining a maximum charging current MAP without lithium precipitation, and determining a battery lithium precipitation-free fast charging method, including:

based on the target model, acquiring corresponding boundary currents when triggering lithium precipitation under any temperature and different charge states, and drawing a lithium precipitation triggering current curve about the charge states and the boundary currents; drawing a trigger lithium-precipitation current curve at the temperature by a curve fitting or interpolation mode through boundary currents corresponding to a plurality of set charge states;

combining trigger lithium precipitation current curves at any temperature to form maximum lithium-free charging current MAP;

and changing the charging current based on the maximum charging current MAP without lithium precipitation, so that the battery can be charged in the shortest time without lithium precipitation.

The battery is charged in the shortest time under the condition of no lithium precipitation, namely, the battery is charged by a current value which is close to the boundary current and smaller than the boundary current, so that the battery is charged by the largest charging current under the condition of no lithium precipitation, and the charging time is shortened.

Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages:

1. according to the invention, the target model is obtained by comparing the first charging data and the second charging data at a plurality of test temperatures, and then the trigger lithium-precipitation current curve at any temperature is predicted by the target model, so that in the charging process, the charging current can be adjusted according to the change of the temperature and the charge state, the charging current is as close to the boundary current as possible but smaller than the boundary current, the battery is ensured to be charged with the maximum charging current in the safe lithium-precipitation boundary, and the rapid charging without lithium precipitation of the battery is realized.

2. The calibration of multiple groups of charging data at different temperatures is utilized, namely, the target model is ensured to meet the precision requirement in the temperature test range, the process does not need to carry out the test at the full temperature, the test times are reduced, and the test cost is reduced.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments, as illustrated in the accompanying drawings.

Drawings

In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a flow chart of a method for battery lithium-ion-free fast-charging in an embodiment of the invention;

FIG. 2 is a dynamic parameter determination process in an embodiment of the present invention;

FIG. 3 is a graph showing the trigger lithium-out current at different test temperatures in an embodiment of the present invention.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

Embodiment one: referring to fig. 1 to 3, a battery lithium-ion-free fast-charging method comprises the following steps:

s1, establishing an electrochemical-thermal coupling heterogeneous model of the battery to be tested without lithium precipitation;

the electrochemical-thermal coupling heterogeneous model comprises an electrochemical model, a thermal model and a lithium separation model. And establishing an electrochemical model according to the liquid phase substance conservation equation, the fixed substance conservation equation, the liquid phase charge conservation equation, the solid phase charge conservation equation, the electrode reaction dynamics equation and the like. And building a thermal model according to an energy conservation equation. And establishing a lithium analysis model according to a lithium analysis reaction kinetic equation.

S2, respectively acquiring a plurality of first charging data at a plurality of test temperatures based on an electrochemical-thermal coupling heterogeneous model;

the temperature of-20 ℃, 0 ℃, 25 ℃ and 45 ℃ is set as the test temperature within the temperature test range of-20 ℃ to 45 ℃.

In the 0% SOC to 100% SOC, 10% SOC, 20% SOC, 30% SOC, 40% SOC, 50% SOC, 60% SOC, 70% SOC, 80% SOC, 90% SOC, and 100% SOC were used as the set state of charge.

Based on the established electrochemical-thermal coupling heterogeneous model, firstly, the simulation charging is predicted to be carried out from 0% SOC to 100% SOC at the temperature of minus 20 ℃, and when the simulation charging is carried out to 10% SOC, 20% SOC, 30% SOC, 40% SOC, 50% SOC, 60% SOC, 70% SOC, 80% SOC, 90% SOC and 100% SOC, the potential of the negative electrode is just equal to 0, lithium precipitation is triggered, and the first charging data of the simulation charging is obtained. The first charging data includes full battery voltage-time data (full battery voltage data with time), negative electrode voltage-time data (negative electrode voltage data with time), and in the simulation charging process, each charging current corresponding to triggering lithium precipitation when the state of charge is set is the boundary current. The above steps were repeated to predict the first charge data at 0 ℃, 25 ℃, 45 ℃ respectively.

S3, acquiring a plurality of second charging data by using a three-electrode test method;

charging the battery to be tested at-20 ℃, 0 ℃, 25 ℃ and 45 ℃ in sequence, and obtaining second charging data of the battery to be tested under the same test temperature and set charge state by using a three-electrode test method. The second charge data includes full battery voltage-time data, negative electrode voltage-time data.

S4, matching the corresponding first charging data with the corresponding second charging data to obtain a target model;

RMSE (root mean square error ) is calculated from a plurality of corresponding first and second charge data at-20 ℃, 0 ℃, 25 ℃, 45 ℃ in order.Wherein->For the first charging data, +.>For the second charging data->For the corresponding charge data amount, for example, 10 sets of data are included in the first charge data, +.>=10。/>Is->The>And charging data.

Comparing the calculated RMSE with a preset error, and adjusting the dynamic parameters of the electrochemical-thermal coupling heterogeneous model when the RMSE is larger than the preset error. The method for adjusting the kinetic parameters can use the existing genetic algorithm and the like. And S2, repeating the steps S4, acquiring first charging data of a simulation charging process of triggering lithium precipitation by a plurality of charge states at each test temperature, and calculating the RMSE. And obtaining a target model until the RMSE calculated at each test temperature is less than or equal to a preset error.

And drawing a trigger lithium-precipitation current curve at each test temperature according to the obtained multiple groups of data of the set charge state and the boundary current at each test temperature.

S5, based on the target model, acquiring a maximum charging current MAP without lithium precipitation, and determining a quick charging method without lithium precipitation of the battery;

based on the target model, obtaining corresponding boundary currents when triggering lithium precipitation under any temperature and different charge states, and drawing a lithium precipitation triggering current curve related to the charge states and the boundary currents.

Combining trigger lithium precipitation current curves at different temperatures to form maximum lithium-free charging current MAP;

and changing the charging current based on the maximum charging current MAP without lithium precipitation, so that the battery is charged under the condition of approaching to the boundary current but without lithium precipitation, and the quick charging without lithium precipitation of the battery is realized.

The principles and embodiments of the present invention have been described in detail with reference to specific examples, which are provided to facilitate understanding of the method and core ideas of the present invention; meanwhile, as those skilled in the art will have variations in the specific embodiments and application scope in accordance with the ideas of the present invention, the present description should not be construed as limiting the present invention in view of the above.

Claims (4)

1. The battery lithium-precipitation-free quick-charging method is characterized by comprising the following steps of:

establishing an electrochemical-thermal coupling heterogeneous model of a battery to be tested, wherein the electrochemical-thermal coupling heterogeneous model comprises an electrochemical model, a thermal model and a lithium separation model;

based on the electrochemical-thermal coupling heterogeneous model, performing simulated charging at least two test temperatures to obtain first charging data when a plurality of set charge states trigger lithium precipitation respectively at each test temperature; the method specifically comprises the following steps: selecting at least three temperatures as test temperatures in a temperature test range; selecting a plurality of charge states from 0% SOC to 100% SOC as set charge states; based on the electrochemical-thermal coupling heterogeneous model, sequentially performing simulation charging from 0% SOC to 100% SOC at a plurality of test temperatures, and obtaining first charging data of the simulation charging when the potential of the negative electrode is equal to zero during the simulation charging to each set charge state;

acquiring second charging data corresponding to the first charging data by using a three-electrode test method;

matching the corresponding first charging data with the corresponding second charging data to obtain a target model; the method specifically comprises the following steps: calculating RMSE from the first charge data and the second charge data corresponding at the test temperature; comparing the calculated RMSE with a preset error, and when the RMSE is larger than the preset error, adjusting the dynamic parameters of the electrochemical-thermal coupling heterogeneous model to acquire first charging data at each test temperature again; repeating the steps until the RMSE calculated at each test temperature is less than or equal to a preset error to obtain a target model; the charging data includes at least one of full-cell voltage-time data and negative electrode voltage-time data or positive electrode voltage-time data; the kinetic parameters comprise solid phase diffusion coefficient, liquid phase diffusion coefficient, reaction rate constant and ion conductivity;

and acquiring a maximum charging current MAP without lithium precipitation based on the target model, and determining a quick charging method without lithium precipitation of the battery.

2. The battery lithium-ion-free fast-charging method according to claim 1, characterized in that: and taking two boundary temperatures in the temperature test range and at least one internal temperature between the two boundary temperatures as test temperatures.

3. The battery lithium-ion-free fast-charging method according to claim 1, characterized in that: and selecting a plurality of charge states from the 0% SOC to 100% SOC at intervals as the set charge states.

4. The battery lithium-ion-free fast-charging method according to claim 1, characterized in that: based on the target model, obtaining a maximum charging current MAP without lithium precipitation, and determining a battery lithium precipitation-free quick charging method, wherein the method comprises the following steps:

based on the target model, acquiring corresponding boundary currents when triggering lithium precipitation under any temperature and different charge states, and drawing a lithium precipitation triggering current curve about the charge states and the boundary currents;

combining trigger lithium precipitation current curves at different temperatures to form maximum lithium-free charging current MAP;

and changing the charging current based on the maximum charging current MAP without lithium precipitation, so that the battery can be charged in the shortest time without lithium precipitation.