Pre-discharge process for lithium-manganese battery

Abstract

The application discloses a pre-discharge process of a lithium-manganese battery, which comprises three constant-current discharge stages in sequence, the current of each stage presents a decreasing trend, the current reduction between adjacent stages is controlled within the range of 10-20 mA, and the discharge current of all stages meets the process requirement of 60-100 mA. The pre-discharge process adopts the strategy of constant-current pre-discharge and decreasing current with voltage attenuation, high-charging-segment large current is used to shorten time, and low-charging-segment small current is used to inhibit polarization deterioration. Compared with a single constant-current scheme, the total discharge time is shortened, and polarization is controlled, so that the average value of the internal resistance of the aged battery is reduced, and the consistency of the internal resistance and voltage of the battery is obviously improved.

Description

Technical Field

[0001] This invention relates to the field of batteries, and in particular to a pre-discharge process for lithium manganese batteries. Background Technology

[0002] Lithium-manganese batteries are widely used in various electronic devices due to their high energy density and excellent long-term storage performance. However, during the production and use of batteries, the positive electrode material manganese dioxide (MnO2) often exists in the form of hydrated manganese dioxide (MnO2·H2O), which contains trace amounts of water of crystallization within its crystal lattice.

[0003] MnO2·H2O exhibits strong catalytic activity, catalyzing the decomposition of organic solvents such as propylene carbonate (PC) in the electrolyte within the battery, generating gaseous products. This reaction not only leads to increased internal pressure and gas expansion within the battery, but in severe cases, it can also significantly increase the battery's internal resistance, directly affecting its discharge performance and long-term storage stability.

[0004] To eliminate the adverse effects of water of crystallization in MnO2·H2O, the commonly used method is pre-discharge treatment. The principle is that during the discharge process, the negative electrode lithium metal loses electrons to generate lithium ions (Li+). + Lithium ions migrate to the positive electrode and embed themselves in the hydrated manganese dioxide (MnO2·H2O) structure, where they interact with hydrogen ions (H+). + A displacement reaction occurs, producing Li. X MnO2 and H + H + It further combines with the migrated electrons, ultimately participating in the formation of stable products or being consumed in the form of hydrogen atoms. Through this reaction, the catalytic activity of manganese dioxide can be effectively reduced, achieving the purpose of removing moisture and stabilizing battery performance.

[0005] In actual production, constant resistance pre-discharge is adopted by most companies due to its ease of operation and high efficiency. This method uses the battery as a power source and discharges it through an external constant resistor. However, in actual production, due to slight fluctuations in manufacturing processes such as the thickness of the battery's positive electrode, the degree of electrolyte wetting, and the tightness of internal assembly, differences in internal resistance are inevitable between different batteries. Under this premise, the constant resistance discharge method has the following obvious defects: (1) Poor discharge depth consistency: According to the formula Q=I×t=(U / R)×t, under the same external resistance R and the same discharge time t, the voltage U is different due to the difference in battery internal resistance, and the actual discharge capacity Q is deviated. After the discharge, the open circuit voltage of the battery shows a large dispersion, which makes it difficult to meet the requirements of voltage consistency for subsequent group use; (2) Excessive polarization leads to over-discharge: The existing constant resistance pre-discharge usually applies a 6.8Ω load resistance, which corresponds to a relatively large discharge current (generally reaching about 200~300mA). Under this current density, electrochemical polarization and concentration polarization are significant, and the battery voltage decays rapidly to below 1.0V. Over-discharge will aggravate the loss of negative electrode lithium and electrolyte decomposition, which will worsen the voltage and internal resistance consistency of the battery after aging.

[0006] Existing technologies also propose using a single current for constant current pre-discharge (such as 300mA or 800mA). It has been found that although 800mA can reduce the internal resistance of the battery after aging, the large current throughout the process leads to severe polarization and limited improvement in voltage consistency; while 300mA is inefficient and has a high internal resistance after aging.

[0007] In summary, existing pre-discharge schemes cannot simultaneously achieve the dual goals of reducing the internal resistance of the battery after aging and improving the voltage-internal resistance consistency after aging: the constant resistance scheme results in uneven discharge depth and large voltage dispersion due to the current decaying with voltage and being affected by individual battery differences; the single constant current scheme faces the dilemma of current selection - low current has low efficiency and high internal resistance after aging, while high current has severe polarization and poor voltage consistency. Summary of the Invention

[0008] The purpose of this invention is to provide a pre-discharge process for lithium manganese batteries.

[0009] The technical solution to achieve the purpose of this invention is: a pre-discharge process for a lithium manganese battery, comprising three constant current discharge stages performed sequentially, wherein the current in each stage decreases gradually, and the current drop between adjacent stages is controlled within the range of 10 to 20 mA, and the discharge current in all stages meets the process requirement of 60 to 100 mA.

[0010] This invention employs constant current pre-discharge. Based on the formula Q=I×t, under the same current I and the same discharge time t, the actual discharge capacity Q is not affected by the difference in battery internal resistance, ensuring that all batteries in the same batch have a consistent depth of discharge, meeting the voltage consistency requirements for subsequent pairing. Simultaneously, since the open-circuit voltage of a new battery is mainly determined by the properties of the positive and negative electrode active materials, the initial open-circuit voltage of batteries in the same batch is basically consistent, resulting in good battery voltage consistency after pre-discharge. Furthermore, to further optimize polarization management and efficiency, this invention designs the pre-discharge process as a three-stage constant current mode, with the current decreasing in each stage. Since the voltage itself continuously decays during pre-discharge, a strategy of decreasing current as the voltage decays is adopted to achieve the optimized effect of fast discharge at high voltage and slow discharge at low voltage: a large current shortens the time in the high-charge stage, and a small current suppresses polarization deterioration in the low-charge stage. Compared to a single constant current scheme, this method shortens the total discharge time and makes polarization controllable, resulting in a decrease in the average internal resistance of the battery after aging, to below 6Ω. Simultaneously, the relative standard deviations (RSDs) of the internal resistance and voltage after aging are within 10% and 0.5%, respectively, showing a significant improvement in consistency compared to existing constant resistance pre-discharge (voltage RSD: 27.86%, internal resistance RSD: 1.18%) and constant current pre-discharge (voltage RSD: 19.83%, internal resistance RSD: 0.95%) methods. Furthermore, existing research indicates that batteries pre-discharged with a relatively large current show a significantly smaller increase in internal resistance after high-temperature storage compared to batteries pre-discharged with a small current (see "Zhang Shiyi, Chen Liming, et al., Relationship between Constant Current Pre-discharge and Electrical Performance of Lithium-Manganese Batteries, Battery, Vol. 52, No. 1, 2022"). This mechanism mainly stems from the fact that high current pre-discharge can damage the passivation film on the surface of the negative electrode lithium metal. However, a higher discharge current is not always better. Excessive discharge current will lead to excessively fast discharge speed, causing problems such as excessive voltage decay, increased polarization resistance, and local overheating, which will damage battery performance and safety. Considering the above factors, this invention locks the pre-discharge current in the range of 60-100mA, and the current drop between adjacent stages is in the range of 10-20mA, balancing the passivation film removal effect with the controllability of the discharge process.

[0011] Furthermore, the three constant current discharge stages are as follows: (1) First stage: When the voltage of all batteries in the same batch to be pre-discharged is >2.5V, apply a constant current of 90-100mA to the batch of batteries for pre-discharge; (2) Second stage: When the voltage of the batch of batteries drops to the range of 2.0 to 2.5V, adjust the current to 70 to 80mA and continue constant current pre-discharge; (3) Third stage: When the voltage of the batch of batteries is in the range of 2.0±0.05V, adjust the current to 60~70mA and continue to perform constant current pre-discharge.

[0012] When the battery voltage is above 2.5V, the corresponding current selection is 90–100mA. At this stage, the battery has a high state of charge and low internal resistance, allowing it to withstand a larger current. This larger current accelerates the initial discharge and effectively breaks down the passivation film on the negative electrode surface. When the voltage drops to the 2.0–2.5V range, the corresponding current selection is 70–80mA. At this point, the voltage enters a moderate level, and electrode polarization gradually becomes apparent. The current is appropriately reduced to control the degree of polarization and maintain discharge stability. When the voltage approaches the target cutoff voltage of 2.0V (i.e., 2.0 ± 0.05V), the corresponding current selection is 60–70mA. At this stage, the battery's internal resistance increases relatively. A smaller current is used to avoid the risk of over-discharge, ensuring precise voltage control at the target threshold while minimizing damage to the electrode structure caused by final polarization.

[0013] Furthermore, the current drop in the second stage relative to the first stage is greater than the current drop in the third stage relative to the second stage. For example, the current drop in the first stage relative to the second stage is 20 mA, while the current drop in the third stage relative to the second stage is 10 mA. Initially, a relatively high decrease rate is used to utilize the low internal resistance characteristic of the high-charge region, allowing for rapid passage through the efficient discharge region. At higher voltages, the advantage of large current surges breaking through the passivation film is fully utilized, shortening the overall pre-discharge time. Later, a more gradual decrease strategy is adopted, enabling fine-grained current control in the voltage-sensitive region (close to 2.0V), avoiding voltage overshoot or bounce caused by sudden current changes. Detailed Implementation

[0014] The preferred embodiment of the pre-discharge process of the lithium manganese battery of the present invention will be described in detail below. Example 1

[0015] Take the CR2032 lithium manganese battery as an example.

[0016] A pre-discharge process for a lithium manganese battery includes three sequential constant-current discharge stages. The current in each stage decreases in a stepwise manner, and the current drop between adjacent stages is controlled within the range of 10–20 mA. The discharge current in all stages meets the process requirement of 60–100 mA. The specific design is as follows: (1) First stage: When the voltage of all batteries in the same batch to be pre-discharged is >2.5V, apply a constant current of 95mA to the batch of batteries for pre-discharge; (2) Second stage: When the voltage of the batch of batteries drops to the range of 2.0 to 2.5V, adjust the current to 75mA and continue constant current pre-discharge; (3) Third stage: When the voltage of the batch of batteries is in the range of 2.0±0.05V, the current is adjusted to 65mA and constant current pre-discharge is continued.

[0017] After using the pre-discharge process of Example 1, the open-circuit voltage and internal resistance test data of 50 CR2032 batteries after high-temperature aging and storage are shown in Table 1 below.

[0018] Table 1

[0019] The pre-discharge process of Embodiments 2-4 of the present invention differs from that of Embodiment 1 only in the current setting values ​​for each stage. The current setting values ​​for each stage of Embodiments 1-4 of the present invention are shown in Table 2 below.

[0020] Table 2

[0021] Meanwhile, the existing constant resistance (6.8Ω) pre-discharge process and constant current (80mA throughout) pre-discharge process were used as Comparative Example 1 and Comparative Example 2. The open circuit voltage and internal resistance test data of 50 CR2032 batteries from Comparative Example 1 and Comparative Example 2 after storage under a 40℃ high-temperature aging process are shown in Tables 3 and 4, respectively.

[0022] Table 3

[0023] Table 4

[0024] After the batteries of Examples 1 to 4 of the present invention, as well as Comparative Examples 1 and 2, were stored at high temperature, the consistency data of open-circuit voltage and internal resistance were statistically analyzed, as shown in Table 5 below.

[0025] Table 5

[0026] As shown in Table 5, compared with the existing constant resistance pre-discharge process (Comparative Example 1) and constant current pre-discharge process (Comparative Example 2), the pre-discharge process of the present invention (Examples 1-4) resulted in an average decrease in the internal resistance of the battery after aging, which was below 6Ω. The relative standard deviation (RSD) of the battery internal resistance and opening voltage after aging decreased to below 10% and 0.5%, respectively, indicating a significant improvement in consistency. Compared with Examples 1-3, Example 4 used a relatively high initial decrease rate (-20mA) followed by a gradual decrease (-10mA), resulting in even lower internal resistance and good consistency after aging.

[0027] The pre-discharge process of the lithium manganese battery of the present invention is applicable not only to the CR2032 lithium manganese battery, but also to other types of lithium manganese batteries.

[0028] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent process transformations made using the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A pre-discharge process for a lithium manganese battery, characterized in that: It includes three constant current discharge stages performed sequentially, with the current decreasing in each stage and the current drop between adjacent stages controlled within the range of 10 to 20 mA. The discharge current of all stages meets the process requirement of 60 to 100 mA.

2. The pre-discharge process for the lithium manganese battery according to claim 1, characterized in that, The three constant current discharge stages are as follows: (1) First stage: When the voltage of all batteries in the same batch to be pre-discharged is >2.5V, apply a constant current of 90-100mA to the batch of batteries for pre-discharge; (2) Second stage: When the voltage of the batch of batteries drops to the range of 2.0 to 2.5V, adjust the current to 70 to 80mA and continue constant current pre-discharge; (3) Third stage: When the voltage of the batch of batteries is in the range of 2.0±0.05V, adjust the current to 60~70mA and continue to perform constant current pre-discharge.

3. The pre-discharge process for the lithium manganese battery according to claim 1, characterized in that: The current drop in the second stage relative to the first stage is greater than the current drop in the third stage relative to the second stage.

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