A method for quickly constructing a low-temperature safe charging regime for lithium batteries

Abstract

The present invention discloses a method for rapidly constructing a low-temperature safe charging regime for a lithium battery, which can achieve high-efficiency full charge without lithium plating on the negative electrode, effectively avoid lithium plating on the negative electrode, and rapidly construct a safe and efficient charging regime. First, a three-electrode is in-situ implanted into the lithium battery. Secondly, the battery charging curve at room temperature and the inflection point of the lithium plating characteristic curve of the battery during charging at low temperature are obtained. According to the battery charging curve at room temperature, the expected capacity corresponding to a certain voltage can be known. The constant-current charging cut-off voltage is determined according to the lithium plating voltage, and a "constant-current charging - lithium plating voltage - constant-voltage charging - expected capacity - constant-current charging" cyclic charging regime is formulated until the battery is fully charged. By changing the temperature and current, a charging regime suitable for different working conditions is obtained. This method can achieve high-efficiency full charge while ensuring that there is no lithium plating on the battery, and it is scientific, reasonable, and highly adaptable.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery cells, and particularly relates to a method for quickly establishing a low-temperature safe charging system for lithium batteries. Background Art

[0002] As an energy storage power system, lithium batteries are often used in many fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. At present, lithium batteries have gradually expanded into fields such as electric bicycles and electric vehicles. However, with the arrival of winter in the north, the environmental temperature decreases, and problems in the actual application of lithium batteries have gradually emerged. Among them, the cruising range drops sharply, the charging battery bulges, and the battery life decreases, etc., and faults occur frequently.

[0003] The working principle of a lithium battery is that lithium ions migrate between the positive and negative electrodes to achieve energy storage and discharge. Its migration process is greatly affected by temperature. When the temperature decreases, the dynamics of the positive and negative electrode materials of the battery become worse, the viscosity of the electrolyte increases, and the conductivity decreases, etc., resulting in a small discharge capacity of the battery and a short cruising range; the polarization of the charging battery is large, and lithium deposition on the negative electrode is likely to occur. In severe cases, it will pierce the diaphragm, causing the battery to short-circuit and catch fire. Among them, low-temperature charging causes greater damage to the battery itself and is often irreversible. Therefore, optimizing the charging strategy of lithium batteries under low-temperature conditions is of great significance. The traditional lithium battery specification includes the maximum allowable charging rate of the battery. Some users will make adjustments according to their own application scenarios. Common ways to optimize charging in a low-temperature environment are: adding an external heating device. For example, in patent CN202120056797.2, a heating plate is assembled on the lithium battery shell. This system can use a heating controller and a heating plate to heat the lithium battery in a timely manner in a low-temperature environment, thus avoiding the safety hazards of charging in a low-temperature environment; changing the charging strategy. For example, patent CN201410252579.0 does not rely on external heating, uses a battery management system to detect the battery temperature in real time, and uses the battery management system to read a preset rule, which defines multiple continuous temperature ranges, and each temperature range corresponds to a charging cut-off voltage to ensure that the battery is charged to a specific voltage at a specific rate at a specific temperature without lithium deposition. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for quickly establishing a low-temperature safe charging system for lithium batteries. The premise is to implant three electrodes in-situ in the battery, and determine whether lithium deposition occurs through the inflection point of the three-electrode characteristic curve, which is more accurate. In a low-temperature environment, it is charged at a constant current to the lithium deposition voltage under the maximum allowable charging current, then switched to constant-voltage charging until the expected capacity, and then switched to constant-current charging. Repeat "constant-current charging - lithium deposition potential - constant-voltage charging - expected capacity - constant-current charging" until the battery is fully charged. Compared with traditional charging under low-temperature conditions, this method can ensure efficient full charging without lithium deposition on the negative electrode.

[0005] The present invention is realized through the following technical solutions: A method for quickly constructing a low-temperature charging regime for lithium batteries, and the adopted technical route is as follows:

[0006] 1. Provide a three-electrode battery. Implant the three electrodes during the preparation stage of the lithium battery stack. When stacking, the separator is wound empty at the end, the negative electrode is shifted outwards to leave a vacancy, and the three electrodes are placed in the vacancy. The diameter of the copper wire of the three electrodes selected is as small as possible, preferably less than 40 μm;

[0007] 2. Charge the battery at room temperature with a current not greater than the maximum allowable current I1 of the battery to obtain the corresponding curve of voltage and capacity, denoted as the expected capacity Q (including Q1 / Q2 / Q3...);

[0008] 3. Under low-temperature conditions, charge the battery at a constant current of I1, and simultaneously monitor the battery voltage and the negative electrode potential. Lithium deposition on the negative electrode occurs when the battery voltage drops, the negative electrode potential rises, or the negative electrode potential alone rises when the negative electrode potential is below 0 V. When lithium deposition occurs, record the negative electrode potential and the corresponding battery voltage, and this battery voltage is denoted as the lithium deposition voltage V1;

[0009] 4. When there is no lithium deposition, charge at a constant current - constant voltage until the battery is fully charged; when lithium deposition occurs, charge at a constant current until the lithium deposition voltage V1, and then switch to constant voltage charging until the expected capacity Q1 at this voltage;

[0010] 5. Then continue to charge with the current I1, monitor the battery voltage and the negative electrode potential, and determine whether lithium deposition occurs according to the inflection point of the negative electrode potential characteristic curve. When lithium deposition occurs, record the negative electrode potential and the battery voltage, and this battery voltage is denoted as the lithium deposition voltage V2;

[0011] 6. When there is no lithium deposition, start from the starting voltage V1, charge at a constant current until the maximum allowable voltage of the battery - constant voltage charge until the battery is fully charged; when lithium deposition occurs, start from the starting voltage V1, charge at a constant current until the lithium deposition voltage V2, and then switch to constant voltage charging until the expected capacity Q2 at this voltage;

[0012] 7. Then continue to charge with the current I1, repeat steps 5 and 6. When there is no lithium deposition, start from the starting voltage V2, charge at a constant current - constant voltage until fully charged. When lithium deposition occurs, start from the starting voltage V2, charge at a constant current - lithium deposition voltage V3 - constant voltage - expected capacity Q3, repeat multiple times... until the battery is fully charged;

[0013] 8. That is, obtain the charging regime for the current I1 at this low temperature, and change the temperature and charging rate to provide a charging regime for lithium battery charging at any low temperature and any current.

[0014] Advantages of the present invention: The method for rapidly establishing a low-temperature safe charging system for lithium batteries of the present invention implants a three-electrode in situ without damaging the battery body. The lithium deposition potential is determined by the potential characteristic curve of the three electrodes. When the lithium deposition potential is reached, the constant current charging is adjusted to constant voltage charging until the capacity reaches the expected value, and then the constant current charging is resumed. The process of "constant current charging - lithium deposition potential - constant voltage charging - expected capacity - constant current charging" is repeated to complete the full charge of the battery at low temperature, so as to achieve high-efficiency full charge without lithium deposition on the negative electrode.

[0015] The method for rapidly establishing a low-temperature safe charging system for lithium batteries of the present invention efficiently completes the charging process of the battery under low-temperature conditions without lithium deposition on the negative electrode. By changing the temperature and current, a charging system for all application scenarios of the battery can be formulated. Compared with the traditional charging method under low-temperature conditions, this method can ensure high-efficiency full charge without lithium deposition on the negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a technical roadmap for rapidly establishing a low-temperature safe charging system for lithium batteries of the present invention.

[0017] Figure 2 It is a characteristic curve diagram of low-temperature safe charging in Example 1 of the present invention (charged to 4.01V, the arrow corresponds to the inflection point), where a is the battery voltage curve and b is the negative electrode potential curve. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] To facilitate the understanding of the present invention, the following examples are listed. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other inventions obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work belong to the scope of protection of the present invention.

[0019] Taking a 4Ah LCO / graphite system battery cell as an example, a three-electrode battery is provided. The three electrodes are implanted during the preparation of the lithium battery stack. When stacking, the separator is wound empty at the end, and the negative electrode is moved outwards to leave a vacancy, and the three electrodes are placed in the vacancy.

[0020] Example 1

[0021] The method for rapidly establishing a low-temperature safe charging system for lithium batteries in this example is as follows:

[0022] (1) Charge the battery at 0.5C at room temperature, and record the corresponding relationship between the capacity and the voltage;

[0023] (2) Charge the battery at 0.5C in an environment of 0°C. When the negative electrode potential is -44 mV and the battery voltage is 4.01V, an inflection point of the characteristic curve appears. The expected capacity corresponding to 4.01V of the normal-temperature battery is 2.809 Ah;

[0024] (3)The battery is charged at a constant current of 0.5C to 4.01V at 0°C, then switched to constant voltage charging at 4.01V until the capacity reaches 2.809Ah. Then, it is charged at a constant current of 0.5C again. At the negative electrode potential of -39mV and the battery voltage of 4.15V, an inflection point of the characteristic curve appears. The expected capacity at this voltage is 3.416Ah. Then, the battery is charged at a constant current of 0.5C starting from 4.01V to 4.15V, switched to constant voltage charging at 4.15V until the capacity reaches 3.416Ah. Then, it is charged at a constant current of 0.5C again. When it is charged to 4.2V, no inflection point of the characteristic curve is found. Therefore, the 0.5C charging strategy in this 0°C environment is optimized as follows: charge at a constant current of 0.5C to 4.01V, switch to constant voltage charging at 4.01V until the capacity reaches 2.809Ah, switch to constant current charging at 0.5C to 4.15V, switch to constant voltage charging at 4.15V until the capacity reaches 3.416Ah, switch to constant current charging at 0.5C to 4.2V, and switch to constant voltage charging at 4.2V to fully charge the battery.

[0025] Example 2

[0026] The method for quickly establishing a low-temperature safe charging system for lithium batteries in this example is as follows:

[0027] (1)Charge the battery at 0.2C at room temperature and record the corresponding relationship between capacity and voltage;

[0028] (2)Charge the battery at 0.2C in an environment of 5°C. No inflection point of the lithium deposition characteristic curve is found. Therefore, the 0.2C charging strategy in this 5°C environment is optimized as charging at a constant current of 0.2C to 4.2V and then switching to constant voltage charging at 4.2V until fully charged.

[0029] The above-described embodiments merely represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A method for quickly constructing a low-temperature safe charging system for lithium batteries, characterized in that, The method includes the following steps: (1) In-situ implant a three-electrode into a lithium battery; (2) Charge at a current not greater than the maximum allowable current of the battery at room temperature; (3) Charge at the current in step (2) under low-temperature conditions, and determine whether lithium plating occurs in the battery according to the characteristic curve of the three-electrode; when there is no lithium plating, charge the battery to full charge in the "constant current charging - constant voltage charging" mode; when the lithium plating potential is reached, switch to the "constant current charging - lithium plating voltage - constant voltage charging - expected capacity - constant current charging" cycle method to charge the battery until it is full; thus obtaining the charging regime for this current at this low temperature; In step (2), charge at a current not greater than the maximum allowable current of the battery at room temperature, record the voltage-capacity curve, and this capacity is recorded as the expected capacity.

2. The method for quickly constructing a low-temperature safe charging system for a lithium battery according to claim 1, wherein In step (1), when stacking the lithium battery, use a diaphragm empty roll to finish, and move the negative electrode outwards to leave a position for implanting the three-electrode.

3. The method for quickly constructing a low-temperature safe charging system for a lithium battery according to claim 1, wherein In step (3), to determine lithium plating in the battery, it is necessary to monitor both the battery voltage and the negative electrode potential during the charging process. When the negative electrode potential drops below 0V and an inflection point of the lithium plating characteristic curve appears, record the negative electrode potential at the lithium plating inflection point and the corresponding battery voltage. At this time, the battery voltage is recorded as the lithium plating voltage.

4. The method for quickly constructing a low-temperature safe charging system for a lithium battery according to claim 1, characterized in that, In step (3), it is determined that the inflection point of the lithium plating characteristic curve is a decrease in the battery voltage, an increase in the negative electrode potential, or an increase in the negative electrode potential alone during the charging process.

5. The method for quickly constructing a low-temperature safe charging system for a lithium battery according to claim 1, characterized in that, In step (3), when charging at the current in step (2) under low-temperature conditions without lithium plating, charge at this current until the maximum allowable voltage of the battery is reached and then switch to constant voltage charging until the battery is full.

6. The method for quickly constructing a low-temperature safe charging system for a lithium battery according to claim 1, characterized in that, In step (3), when lithium plating occurs during charging at the current in step (2) under low temperature, the battery is charged at a constant current until the lithium plating voltage, then switched to constant voltage charging until the expected capacity at this voltage. On this basis, repeat step (3) until the battery is full.

7. The method for quickly constructing a low-temperature safe charging system for a lithium battery according to claim 1, wherein, According to the actual charging curves in steps (2)-(3), change the temperature and current to obtain a charging regime suitable for different working conditions.

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