KR102511976B1 - Fast charge method to prevent lithium plating in an electric vehicle lithium-ion battery - Google Patents

Abstract

The present invention relates to a rapid charging method for preventing lithium precipitation of a lithium ion battery of an electric vehicle.
A rapid charging method for preventing lithium precipitation of a lithium ion battery of an electric vehicle according to the present invention includes the steps of performing a basic performance test of a battery cell and a charging characteristic test for extracting modeling parameters; extracting modeling parameters for predicting electrical and thermal behavior of the battery cell that has undergone the test; Obtaining an inflection point of a voltage curve according to the charged charge amount using a dV / dQ curve, and determining the inflection point as a point where lithium precipitation occurs; and deriving a lithium precipitation line in the SOC section where charging is performed at a point where lithium precipitation occurs, and performing rapid charging along a safety limit line having a predetermined safety margin value from the derived lithium precipitation line.
According to the present invention, when a lithium ion battery for an electric vehicle is rapidly charged, lithium is deposited on the surface of the negative electrode by performing rapid charging in consideration of the charging time and the electrical and thermal characteristics of the battery cell along the set safety limit line. It has the advantage of prolonging the life of the battery, securing safety, and obtaining maximum efficiency for a given operating condition and a specific safety margin.

Description

Fast charge method to prevent lithium plating in an electric vehicle lithium-ion battery}

The present invention relates to a rapid charging method for preventing lithium precipitation of a lithium ion battery for an electric vehicle, and more particularly, during rapid charging of a lithium ion battery for an electric vehicle, by preventing lithium from precipitating on the surface of a negative electrode, It relates to a rapid charging method for preventing lithium precipitation of a lithium ion battery of an electric vehicle that can secure lifespan and safety.

In order to achieve the greenhouse gas reduction target, the domestic and overseas electric vehicle market is expanding and related technology development is actively progressing. In order to accelerate the supply and spread of these electric vehicles, the development of fast charging technology that can extend the mileage and shorten the charging time must be supported. However, when the charging rate is too high, lithium plating occurs on the surface of the negative electrode instead of being inserted into the negative electrode. This accelerates deterioration and corrosion of the lithium ion battery, causing a decrease in capacity and performance of the battery, and may also cause safety problems. Therefore, it is important to find the optimal rapid charging protocol under conditions where lithium plating does not occur, and predicting the effect of rapid charging on the electrical and thermal behavior of lithium ion batteries is important for rational energy storage system design. It is essential.

Since rapid charging applies a higher current than normal charging, intercalation and deintercalation rates of lithium ions in the electrode cannot sufficiently follow the applied current. This increases the speed of a side reaction that degrades the electrode material, which increases the resistance of the lithium secondary battery and causes the temperature to rise excessively during charging, resulting in a relatively rapid decrease in the cycle life of the lithium secondary battery. do.

Therefore, research on optimal charging conditions capable of reducing the temperature rise of the lithium secondary battery and shortening the charging time is absolutely necessary in order to maximize the lifespan of the lithium secondary battery in all fields where it is actually used.

On the other hand, Korean Patent Publication No. 10-2017-0021630 (Patent Document 1) discloses a "battery charge limit prediction method and battery rapid charging method and device using the same", and the battery charging method according to this is a unit cell and A data acquisition step of measuring a cathode potential according to a state of charge (SOC) for each different charging rate through a three-electrode cell experiment having a reference electrode; determining a point at which the negative electrode potential does not fall and becomes constant from the obtained data as a point at which Li-plating occurs and setting it as a charging limit to obtain a protocol for gradually changing the charging rate; and charging the battery with the above protocol.

In the case of Patent Document 1 as described above, the point at which the negative electrode potential starts to become constant without dropping is determined as the Li-plating occurrence point and set as the charging limit, so the battery is at risk of reaching the Li-plating limit during charging. Since the charging current is reduced stepwise at the charging limit point, the maximum charging efficiency cannot be achieved in a given charging time. Therefore, it is essential to introduce a charging method based on the concept of a margin of safety (MS) that prevents Li-plating from occurring fundamentally, and the charging current is also reduced in a cascading manner to achieve maximum efficiency within a given charging time. need to achieve

Korean Patent Publication No. 10-2017-0021630 (published on February 28, 2017)

The present invention was created in consideration of the above matters comprehensively, and is an electric vehicle capable of securing the lifespan and safety of the battery by preventing the precipitation of lithium on the surface of the negative electrode during rapid charging of a lithium ion battery for an electric vehicle. Its purpose is to provide a rapid charging method for preventing lithium precipitation of a lithium ion battery.

In addition, another object of the present invention is to set a specific safety limit line having a constant safety margin value from the lithium precipitation line so that lithium plating does not fundamentally occur, and to reduce the charging current along the line continuously rather than stepwisely. To achieve maximum efficiency in a timely manner.

In order to achieve the above object, the rapid charging method for preventing lithium precipitation of an electric vehicle lithium ion battery according to the present invention,

As a rapid charging method to secure the life and safety of the battery by preventing the precipitation of lithium on the surface of the negative electrode during rapid charging of lithium ion batteries for electric vehicles,

a) performing a basic performance test of a battery cell and a charging characteristic test for extracting modeling parameters;

b) extracting modeling parameters for predicting electrical and thermal behavior of the battery cell that has performed the test;

c) obtaining an inflection point of a voltage curve according to the amount of charged charge using a dV/dQ curve, and determining the inflection point as a point where lithium plating occurs; and

d) A lithium precipitation line is derived from the state of charge (SOC) section where charging is performed for the point where lithium precipitation occurs, and rapid charging is performed along a safety limit line having a constant safety margin value from the derived lithium precipitation line. Its feature is that it includes steps to perform.

Here, the basic performance test of the battery cell in step a) may include a voltage characteristic test, a current characteristic test, and a temperature characteristic test of the battery cell.

In addition, modeling parameters for predicting electrical and thermal behavior of the battery cell in step b) may include U and Y.

In addition, a lithium precipitation line may be set in a section where charging is performed by using linear interpolation and extrapolation for the point where lithium precipitation occurs in step c).

In addition, in performing rapid charging along the safety limit line set in step d), rapid charging may be performed in consideration of the charging time and electrical and thermal characteristics of the battery cell along the set safety limit line.

In addition, in order to determine the safety level of the fast charging algorithm according to the safety limit line, a quantified index, MS (margin of safety), is introduced to determine the safety level of the fast charging algorithm according to the safety limit line according to the magnitude of the MS value. A step of determining may be further included.

At this time, as a concept representing the efficiency of a specific charging protocol, the efficiency of the charging protocol is quantified by introducing the FF (fill factor), which is defined as the area ratio of the charging current to the SOC of the specific charging protocol and safety limit line within a given charging SOC range. The step of determining as may be further included.

In addition, in performing rapid charging along the safety limit line set in step d), the starting current is fixed to a specific current value, and then the current follows the safety limit line having a specific margin with respect to the lithium deposition line. Fast charging may be performed by applying a variable current protocol (VCP).

At this time, the specific current value may be 130A, and the specific margin may be 20%.

In addition, by predicting the electrical and thermal behavior of the battery cell using the electrical and thermal behavior prediction model of the battery cell during rapid charging, the step of determining whether the battery voltage and battery temperature is out of the safe operating range of the battery recommended by the battery manufacturer can include more.

In addition, the feasibility of the modeling is determined by comparing the electrical and thermal behavior prediction results of the battery cell using the electrical and thermal behavior prediction model of the battery cell during rapid charging with the results of actually measuring the electrical and thermal behavior of the battery cell through tests. A step of verifying may be further included.

The method may further include verifying validity of the fast charging algorithm through a discharge test after charging the battery cell with the fast charging algorithm according to the safety limit line.

According to the present invention, during rapid charging of a lithium ion battery for an electric vehicle, charging is performed along the set safety limit line to prevent lithium precipitation on the surface of the negative electrode, thereby extending the life of the battery and securing safety, It has the advantage of obtaining maximum efficiency for a given operating condition and a specific safety margin.

1 is a flowchart showing the execution process of a rapid charging method for preventing lithium precipitation of a lithium ion battery for an electric vehicle according to the present invention.
2 is a diagram showing the results of performing a basic performance test of a battery cell according to the fast charging method of the present invention.
3 is a diagram showing modeling parameter extraction for predicting electrical and thermal behavior of a battery cell according to the fast charging method of the present invention.
4 is a diagram showing an outline of obtaining an inflection point of a voltage curve according to a charging current and determining the inflection point as a point at which lithium precipitation occurs.
5 is a diagram showing an overview of determining the safety level of a fast charging algorithm using MS and an overview of determining the efficiency of a design protocol for a margin line.
6 is a diagram showing a VCP (Variable Current Protocol) fast charging algorithm following a specific margin of a safety limit line employed in the method of the present invention.
7 is a diagram showing an overview of predicting electrical and thermal behavior of a battery cell during rapid charging using a prediction model for electrical and thermal behavior of a battery cell.
8 is a diagram showing a comparison between modeling results and test results of a 20% margin, VCP fast charging algorithm.
9 is a diagram showing the verification result of the VCP fast charging algorithm employed in the present invention.

The terms or words used in this specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventors can properly define the concept of terms in order to best explain their invention. Based on the principle, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

Throughout the specification, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated. In addition, terms such as "...unit", "...unit", "module", and "device" described in the specification mean a unit that processes at least one function or operation, which is hardware or software, or a combination of hardware and software. can be implemented as

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flowchart illustrating an execution process of a rapid charging method for preventing lithium precipitation of a lithium ion battery of an electric vehicle according to an embodiment of the present invention.

Referring to FIG. 1, a rapid charging method for preventing lithium precipitation of a lithium ion battery for an electric vehicle according to the present invention prevents lithium from precipitating on the surface of a negative electrode during rapid charging of a lithium ion battery for an electric vehicle, As a rapid charging method for securing the lifespan and safety of a battery cell, first, a basic performance test of a battery cell and a charging characteristic test for extracting modeling parameters are performed (step S101). Here, the basic performance test of the battery cell may include a voltage characteristic test (A), a current characteristic test (B), and a temperature characteristic test (C) of the battery cell, as shown in FIG. 2 .

In addition, modeling parameters for predicting electrical and thermal behavior of the battery cell that has undergone the test are extracted (step S102). Here, modeling parameters for predicting electrical and thermal behavior of the battery cell are shown in FIG. As noted above, U and Y may be included. U and Y are the main parameters of modeling, J=Y(Vp-Vn), which indicates that the current density (current per electrode unit area; electrochemical reaction rate per electrode unit area) is linearly related to the electrode potential difference (Vp-Vn). It is a parameter entered into the formula of -U). Looking at the physical meaning of U and Y, U means the equilibrium potential of the battery, and Y means the reciprocal of the battery resistance. If the functional relationship between U and Y according to the SOC of the battery is known, the electrical behavior of the battery can be predicted.

In this way, when the modeling parameter extraction for predicting the electrical and thermal behavior of the battery cell is completed, based on it, as shown in FIG. It is obtained using and the inflection point is determined as a point where lithium plating occurs (step S103). Here, a lithium deposition line may be set in a section in which charging is performed using linear interpolation and extrapolation for the point where lithium precipitation occurs.

Then, a lithium precipitation line is derived from the SOC (state of charge) section where charging is performed for the point where lithium precipitation occurs, and rapid charging is performed along a safety limit line having a constant safety margin value from the derived lithium precipitation line. is performed (step S104).

Here, in performing rapid charging along the lithium deposition line set in step S104, rapid charging may be performed in consideration of the charging time and electrical and thermal characteristics of the battery cell along the set safety limit line.

In addition, in order to determine the degree of safety of the fast charging algorithm according to the safety limit line in step S104, as shown in FIG. The method may further include determining the degree of safety of the fast charging algorithm according to the safety limit line according to the magnitude of . Here, MS means the degree of margin that the fast charging algorithm has for the lithium deposition line. As the value of MS _min , which is the point where the MS value is the minimum in the charging range, is larger, it can be determined as a safe fast charging algorithm. At this time, if the value of MS _min is less than or equal to 0, it can be determined as an unsafe algorithm in which lithium precipitation occurs.

In addition, in the method of the present invention, as shown in (B) of FIG. 5, as a concept representing the efficiency of a specific charging protocol, FF defined as the area ratio of the charging current to the SOC of the specific charging protocol and safety limit line within a given charging SOC range A step of quantitatively determining the efficiency of the filling protocol by introducing a fill factor may be further included. At this time, the closer the FF value is to 1, the more efficient the protocol can be determined.

In addition, in performing rapid charging along the safety limit line set in step S104, as shown in FIG. 6, the starting current is fixed to a specific current value, and then the current is set at a specific margin for the lithium deposition line. Fast charging can be performed by applying a variable current protocol (VCP) that follows. At this time, the specific current value may be 130A, and the specific margin may be 20%. Here, setting the starting current to 130A takes into consideration the specifications of the electric vehicle charger. In addition, setting the margin of the lithium deposition line to 20% does not necessarily mean that it is limited to 20%, and may be set to a different value depending on the design purpose of rapid charging, the use environment, and the type and composition of the battery electrode. may be

In addition, as shown in FIG. 7, the rapid charging method of the present invention as described above predicts the electrical and thermal behavior of the battery cell using the electrical and thermal behavior prediction model of the battery cell during rapid charging, thereby predicting the battery voltage and battery A step of determining whether the temperature is out of the safe operating range of the battery recommended by the battery manufacturer may be further included.

In addition, as shown in FIG. 8, the method of the present invention actually predicts the electrical and thermal behavior of the battery cell and the electrical and thermal behavior of the battery cell using the electric and thermal behavior prediction model of the battery cell during rapid charging. A step of verifying validity of the modeling through comparison with a result measured through a test may be further included. The example of FIG. 8 shows the comparison of the modeling results and test results of the 20% margin, VCP fast charging algorithm. In FIG. 8 , (A) represents a comparison result of voltage characteristic curves, (B) represents a comparison result of current characteristic curves, and (C) represents a comparison result of temperature characteristic curves.

In addition, as shown in FIG. 9, the method of the present invention may further include verifying the legitimacy of the fast charging algorithm through a discharge test after charging the battery cell with the fast charging algorithm according to the safety limit line. can That is, since the present invention aims for a fast charging algorithm capable of charging electric energy (cell: 60.74 Wh) capable of traveling 100 km within 10 minutes, the battery cell is charged with the fast charging algorithm according to the present invention and then discharged. The test is to verify the legitimacy of the fast charging algorithm. 9, (A) shows the verification result of the VCP fast charging algorithm as a characteristic graph, and (B) shows the arrival time of charging energy (power) according to the applied current as a table.

Table 1 below compares the results when charging with various fast charging protocols with the same MS _min values along certain safety limit lines. From Table 1, it can be seen that the VCP having the largest FF value has the fastest charging time and the lowest highest voltage. The maximum output and maximum temperature are the same or relatively higher, but at a level that does not impair the safety of the battery. This means that the VCP fast charging algorithm with the largest FF value has excellent performance.

fast charge protocol charging time
[s] highest voltage
[V] peak power
[W] highest temperature
[℃] Li plating Factor Charging method MS _min FF 3 steps 630 3.96 507.9 30.1 0.25 0.88 Step charge 4 steps 615 3.95 507.9 30.3 0.25 0.90 5 steps 600 3.95 507.9 30.4 0.25 0.91 VC 579 3.94 507.9 31 0.25 0.94 VCP

As described above, the rapid charging method for preventing lithium precipitation of a lithium ion battery for an electric vehicle according to the present invention is fast charging the lithium ion battery for an electric vehicle, along the set safety limit line, the charging time and the electrical and By performing rapid charging in consideration of thermal characteristics, the phenomenon of lithium precipitation on the surface of the anode is prevented to extend the life of the battery, secure safety, and to obtain maximum efficiency for given operating conditions and a specific safety margin. there is.

In addition, after charging the battery cell with the fast charging algorithm according to the safety limit line, by verifying the legitimacy of the fast charging algorithm through a discharge test, when the fast charging method according to the present invention is applied to a battery cell for an electric vehicle, a fast time It has the advantage of being able to safely charge within.

Although the present invention has been described in detail through preferred embodiments, the present invention is not limited thereto, and various changes and applications can be made without departing from the technical spirit of the present invention. self-explanatory for technicians Therefore, the true scope of protection of the present invention should be construed by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims (12)

As a rapid charging method to secure the life and safety of the battery by preventing the precipitation of lithium on the surface of the negative electrode during rapid charging of lithium ion batteries for electric vehicles,
a) performing a basic performance test of a battery cell and a charging characteristic test for extracting modeling parameters;
b) extracting modeling parameters for predicting electrical and thermal behavior of the battery cell that has performed the test;
c) obtaining an inflection point of a voltage curve according to the amount of charged charge using a dV/dQ curve, and determining the inflection point as a point where lithium plating occurs; and
d) A lithium precipitation line is derived from the state of charge (SOC) section where charging is performed for the point where lithium precipitation occurs, and rapid charging is performed along a safety limit line having a constant safety margin value from the derived lithium precipitation line. Including the steps to perform,
In step c), a lithium precipitation line is set in a section where charging is performed using linear interpolation and extrapolation for the point where lithium precipitation occurs,
In order to determine the safety level of the fast charging algorithm according to the safety limit line, a quantified index, MS (margin of safety), is introduced to determine the safety level of the fast charging algorithm according to the safety limit line according to the magnitude of the MS value. steps,
As a concept representing the efficiency of a specific charging protocol, the efficiency of the charging protocol is quantitatively determined by introducing the FF (fill factor), which is defined as the area ratio of the charging current to the SOC of a specific charging protocol and safety limit line within a given charging SOC range A rapid charging method for preventing lithium precipitation of an electric vehicle lithium ion battery further comprising the step of doing.
According to claim 1,
The basic performance test of the battery cell in step a) includes a voltage characteristic test, a current characteristic test, and a temperature characteristic test of the battery cell. Rapid charging method for preventing lithium precipitation of a lithium ion battery.
According to claim 1,
In step b), the modeling parameters for predicting the electrical and thermal behavior of the battery cell include U, which means the equilibrium potential of the battery, and Y, which means the reciprocal of the battery resistance. fast charging method for
delete According to claim 1,
In performing rapid charging along the safety limit line set in step d), lithium precipitation of the lithium ion battery of an electric vehicle performing rapid charging in consideration of the charging time and electrical and thermal characteristics of the battery cell along the set safety limit line fast charging method to prevent
delete delete According to claim 1,
In performing rapid charging along the safety limit line set in step d), the starting current is fixed to a specific current value, and then the current is VCP (variable) following the safety limit line having a specific margin of the lithium deposition line. A rapid charging method for preventing lithium precipitation in lithium ion batteries of electric vehicles that perform rapid charging by applying current protocol).
According to claim 8,
The specific current value is 130A, the specific margin is a rapid charging method for preventing lithium precipitation of an electric vehicle lithium ion battery of 20%.
According to claim 1,
Further comprising the step of determining whether the battery voltage and battery temperature are out of the safe operating range of the battery recommended by the battery manufacturer by predicting the electrical and thermal behavior of the battery cell using the electric and thermal behavior prediction model of the battery cell during rapid charging. A rapid charging method for preventing lithium precipitation in lithium ion batteries of electric vehicles.
According to claim 10,
The validity of the modeling is verified by comparing the electrical and thermal behavior prediction results of the battery cell using the electrical and thermal behavior prediction model of the battery cell during rapid charging with the results of actually measuring the electrical and thermal behavior of the battery cell through tests. A rapid charging method for preventing lithium precipitation of an electric vehicle lithium ion battery further comprising the step of doing.
According to claim 1,
After charging the battery cell with the fast charging algorithm according to the safety limit line, the fast charging method for preventing lithium precipitation of the lithium ion battery of an electric vehicle further comprising the step of verifying the legitimacy of the fast charging algorithm through a discharge test.

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