Method for improving cycle performance of lithium battery

Abstract

The present application relates to a method for improving the cycle performance of lithium batteries, belonging to the technical field of battery performance improvement method. The present application solves the technical problem of low service life of lithium batteries in the prior art. The method of the present application: first, before the cycle starts, use the clamp to apply initial pressure P0 to the lithium battery, keep the relative position between the clamps unchanged, cycle M times; then adjust the clamp, apply pressure P1 to the lithium battery, keep the relative position between the clamps unchanged, cycle M times; and so on, until the clamp is adjusted to apply pressure P N to the lithium battery, keep the relative position between the clamps unchanged, cycle M times; N represents the number of times of adjusting the clamp after applying initial pressure P0 to the lithium battery using the clamp, N >= 1, P0 >= P1 >= … >= P N . The method can effectively improve the capacity retention capability of lithium batteries during the cycle process, reduce the capacity attenuation of lithium batteries, and prolong the service life of lithium batteries.

Description

Technical Field

[0001] This invention belongs to the technical field of battery performance improvement methods, specifically relating to a method for improving the cycle performance of lithium batteries. Background Technology

[0002] Lithium-ion batteries are a type of battery that uses lithium metal or lithium alloys as positive / negative electrode materials and a non-aqueous electrolyte solution. Due to their excellent cycle performance, high specific energy and specific power, and lack of memory effect, lithium-ion batteries are increasingly widely used in electric vehicles and energy storage markets.

[0003] The active materials in lithium batteries are generally coated on thin copper and aluminum foil. The electrodes are relatively soft and easily deformed under stress. During long-term charge and discharge cycles, factors such as thermal stress, electrode volume changes, and gas generation may cause deformation of the battery current collector and electrodes, which will reduce the contact between the positive and negative electrodes, increase the difficulty of lithium ion migration in the battery, and lead to increased battery impedance and reduced cycle performance.

[0004] In existing technologies, to improve electrode contact during lithium battery cycling, clamps are typically used to hold the battery in place during cycling to extend its cycle life. However, during charging and discharging, lithium ions continuously insert into and extract from the electrode material, causing the electrode material to expand. For example, Li... x The volume change rate of Mn2O4 increases with increasing lithium-ion intercalation. When x increases from 0.2 to 0.995, its volume increases by 6.5%. (The last sentence appears to be incomplete and possibly refers to a different material, Li.) 1-x Ni 1 / 3 Co 1 / 3 Mn 1 / 3 When the volume of the O2 unit cell changes from x = 0.78 to x = 0, the volume increases by approximately 2%. Furthermore, the change is relatively larger at the negative electrode, where lithium ions intercalate into the graphite layer, forming a series of interlayer compounds, Li. x C6, after full lithiation, has a volume expansion coefficient of 10.4%, while silicon, with its higher specific capacity, has an expansion coefficient as high as 400% after full lithiation. Simultaneously, stress in the lithium battery electrode materials is continuously generated and accumulated during cycling. When the battery is clamped using a fixture, the forces acting on the lithium battery during cycling also continuously accumulate. When the pressure on a lithium battery increases, the ion diffusion factor of both the positive and negative electrodes decreases, with the negative electrode being more significantly affected. Under higher pressure, the diffusion of lithium ions within the negative electrode slows down further, potentially leading to lithium ion accumulation on the negative electrode surface, causing metallic lithium deposition and accelerating the battery's lifespan decline. Furthermore, excessive pressure can also cause localized pores in the separator within the battery, resulting in increased local current density and accelerating the battery's lifespan decline.

[0005] Therefore, although the use of fixtures improves the cycle performance of lithium-ion batteries to some extent, it does not take into account the increased stress accumulation inside the lithium-ion battery during the cycle process. Summary of the Invention

[0006] In view of this, the present invention provides a method to improve the cycle performance of lithium batteries, which addresses the technical problems in the prior art where increased battery stress accumulation during cycling due to thermal stress, electrode volume changes, and gas generation leads to a decrease in ion diffusion coefficient and membrane pore blockage, resulting in battery capacity decay and shortened battery life.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows.

[0008] The method for improving the cycle performance of lithium batteries according to the present invention comprises the following steps:

[0009] Before the cycle begins, apply an initial pressure P0 to the lithium battery using a clamp, keeping the relative positions of the clamps constant, and cycle for M times.

[0010] Adjust the clamps, apply pressure P1 to the lithium battery, keep the relative position between the clamps unchanged, and repeat M times;

[0011] This process continues until the clamps are adjusted to apply pressure P to the lithium battery. N Keep the relative positions between the fixtures unchanged, and repeat the cycle M times;

[0012] Each M represents an integer between 1 and 1000;

[0013] The N represents the number of times the clamp is adjusted after applying the initial pressure P0 to the lithium battery using the clamp, and N≥1;

[0014] The P0≥P1≥…≥P N ;

[0015] The P0, P1, ..., P N Each represents 0 to 2 MPa independently.

[0016] Preferably, the state of charge of the lithium battery is consistent before each adjustment of the fixture; more preferably, the lithium battery is in a depleted state (0% SOC) before each adjustment of the fixture.

[0017] Preferably, the pressure change is constant each time the clamp is adjusted, and the pressure change range is 0.01 to 0.1 MPa.

[0018] Preferably, the clamp is made of one of the following materials: aluminum plate, steel plate, or rubber plate.

[0019] Preferably, the positive electrode material of the lithium battery is one of layered oxide positive electrode material, polyanionic positive electrode material, spinel positive electrode material, and lithium-rich ternary layered positive electrode material.

[0020] Preferably, the negative electrode material of the lithium battery is one of natural graphite, artificial graphite, hard carbon, soft carbon, silicon-carbon, silicon, metallic lithium, and metallic tin.

[0021] Preferably, the lithium battery is a pouch lithium battery or a square lithium battery.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The method for improving the cycle performance of lithium batteries according to the present invention applies initial pressure to the lithium battery using a clamp and gradually adjusts (maintains or reduces) the pressure during the cycle process, which can effectively improve the capacity retention capability of the lithium battery during the cycle process, reduce the capacity decay of the lithium battery, and extend the service life of the lithium battery. Detailed Implementation

[0024] To further understand the present invention, preferred embodiments of the present invention are described below. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0025] The method for improving the cycle performance of lithium batteries according to the present invention comprises the following steps:

[0026] Before the cycle begins, apply an initial pressure P0 to the lithium battery using a clamp, keeping the relative positions of the clamps constant, and cycle for M times.

[0027] Adjust the clamps, apply pressure P1 to the lithium battery, keep the relative position between the clamps unchanged, and repeat M times;

[0028] This process continues until the clamps are adjusted to apply pressure P to the lithium battery. N Keep the relative positions between the fixtures unchanged, and repeat the cycle M times;

[0029] Where M represents an integer between 0 and 1000, preferably an integer between 100 and 600; N represents the number of times the clamp is adjusted after applying initial pressure P0 to the lithium battery using the clamp, N≥1, and the specific number is set according to actual needs. If N=1, there is one adjustment P1; if N=5, there are five adjustments P1, P2, P3, P4, and P5, where P0≥P1≥…≥P N ;P0, P1, ..., P N Each represents 0 to 2 MPa independently.

[0030] In the above technical solution, the pressure change is a constant value each time the clamp is adjusted, preferably 0.01 to 0.1 MPa.

[0031] In the above technical solution, "cycle" refers to charge-discharge cycle, preferably with a rest period of 30 minutes between each cycle, and a charge-discharge voltage range of 3.0–4.15V. However, it should be noted that the present invention does not impose special restrictions on the rest period between cycles and the charge-discharge voltage, which can be set according to actual needs.

[0032] In the above technical solutions, the clamps are not particularly limited and are not an innovation of this invention. Any clamp that can apply the variable pressure of this invention to the lithium battery and ensure that the relative positions between the clamps remain unchanged when the pressure is applied is acceptable. Those skilled in the art can obtain such clamps based on existing technology. The material of the clamps can be one of aluminum plate, steel plate, or rubber plate, or other materials can be selected as needed.

[0033] In the above technical solution, the positive electrode material of the lithium battery can be one of layered oxide positive electrode material, polyanion positive electrode material, spinel positive electrode material, or lithium-rich ternary layered positive electrode material; preferably, it is a nickel-cobalt-manganese ternary material. However, it should be noted that the present invention is not limited thereto, and those skilled in the art can set it according to actual needs.

[0034] In the above technical solution, the negative electrode material of the lithium-ion battery can be one of natural graphite, artificial graphite, hard carbon, soft carbon, silicon-carbon, silicon, metallic lithium, and metallic tin; preferably, it is silicon-carbon material. However, it should be noted that the present invention is not limited thereto, and those skilled in the art can set it according to actual needs.

[0035] In the above technical solution, the lithium battery can be a pouch lithium battery or a prismatic lithium battery; preferably, it is a pouch lithium battery. However, it should be noted that the present invention is not limited thereto, and those skilled in the art can make the appropriate configuration according to actual needs.

[0036] In the above technical solution, the rated capacity of the lithium battery is preferably 30Ah. However, it should be noted that the present invention is not limited to this, and those skilled in the art can set it according to actual needs.

[0037] It is important to note that the state of charge (SOC) of the lithium battery remains consistent before each fixture adjustment. For example, the lithium battery is always in a depleted state (0% SOC).

[0038] The terminology used in this invention generally has the meanings commonly understood by those skilled in the art, unless otherwise stated. To enable those skilled in the art to better understand the technical solutions of this invention, the invention will be further described in detail below with reference to embodiments.

[0039] In the following embodiments, various processes and methods not described in detail are conventional methods known in the art. Unless otherwise specified, the materials, reagents, apparatus, instruments, equipment, etc., used in the following embodiments are commercially available.

[0040] The present invention will be further illustrated below with reference to the embodiments.

[0041] Example 1

[0042] The lithium battery under test is placed between the fixtures. Before the cycle begins, an initial pressure P0 = 1 MPa is applied to the lithium battery using the fixtures, keeping the relative position between the fixtures constant, and the cycle is repeated 100 times. The fixtures are then adjusted to apply a pressure P1 = 0.9 MPa to the lithium battery under test, keeping the relative position between the fixtures constant, and the cycle is repeated 100 times. The fixtures are then adjusted to apply a pressure P2 = 0.8 MPa to the lithium battery under test, keeping the relative position between the fixtures constant, and the cycle is repeated 100 times. The fixtures are then adjusted to apply a pressure P3 = 0.7 MPa to the lithium battery under test, keeping the relative position between the fixtures constant, and the cycle is repeated 100 times. The fixtures are then adjusted to apply a pressure P4 = 0.6 MPa to the lithium battery under test, keeping the relative position between the fixtures constant, and the cycle is repeated 100 times. The entire cycle test is repeated 600 times. The lithium battery under test was a pouch lithium battery with a rated capacity of 30Ah. The positive electrode active material was a nickel-cobalt-manganese ternary material, and the negative electrode active material was silicon-carbon material. Throughout the cycle test, the lithium battery under test was charged and discharged at 1C (30A). The resting time between two consecutive charge / discharge cycles was 30 minutes. The charge / discharge voltage range was 3.0–4.15V. The capacity of the lithium battery under test was measured during the charge / discharge process, and the results are shown in Table 1. Before each fixture adjustment, the state of charge (SOC) of the lithium battery under test was 0%.

[0043] Example 2

[0044] The lithium battery under test is placed between the fixtures. Before the cycle begins, an initial pressure P0 = 0.5 MPa is applied to the lithium battery using the fixtures, keeping the relative position between the fixtures constant, and the cycle is repeated 100 times. The fixtures are then adjusted to apply a pressure P1 = 0.4 MPa to the lithium battery under test, keeping the relative position between the fixtures constant, and the cycle is repeated 100 times. The fixtures are then adjusted to apply a pressure P2 = 0.3 MPa to the lithium battery under test, keeping the relative position between the fixtures constant, and the cycle is repeated 100 times. The fixtures are then adjusted to apply a pressure P3 = 0.2 MPa to the lithium battery under test, keeping the relative position between the fixtures constant, and the cycle is repeated 100 times. The fixtures are then adjusted to apply a pressure P4 = 0.1 MPa to the lithium battery under test, keeping the relative position between the fixtures constant, and the cycle is repeated 100 times. The entire cycle test is repeated 600 times. The lithium battery under test was a pouch lithium battery with a rated capacity of 30Ah. The positive electrode active material was a nickel-cobalt-manganese ternary material, and the negative electrode active material was silicon-carbon material. Throughout the cycle test, the lithium battery under test was charged and discharged at 1C (30A). The resting time between two consecutive charge / discharge cycles was 30 minutes. The charge / discharge voltage range was 3.0–4.15V. The capacity of the lithium battery under test was measured during the charge / discharge process, and the results are shown in Table 1. Before each fixture adjustment, the state of charge (SOC) of the lithium battery under test was 0%.

[0045] Example 3

[0046] The lithium battery under test was placed between the clamps. Before the cycle began, an initial pressure P0 = 0.2 MPa was applied to the lithium battery under test using the clamps, keeping the relative position between the clamps unchanged, and the cycle was repeated for 200 cycles. The clamps were then adjusted to apply a pressure P1 = 0.18 MPa to the lithium battery under test, keeping the relative position between the clamps unchanged, and the cycle was repeated for 200 cycles. The clamps were then adjusted to apply a pressure P2 = 0.16 MPa to the lithium battery under test, keeping the relative position between the clamps unchanged, and the cycle was repeated for 200 cycles. The entire cycle test process consisted of 600 cycles. The lithium battery under test was a pouch lithium battery with a rated capacity of 30 Ah. The positive electrode active material was a nickel-cobalt-manganese ternary material, and the negative electrode active material was a silicon-carbon material. During the entire cycle test, the lithium battery was charged and discharged using 1C (30A). The resting time between two adjacent charge and discharge cycles was 30 min. The voltage range for charge and discharge was 3.0–4.15 V. The capacity of the lithium battery under test was measured during the charge and discharge process, and the results are shown in Table 1. Before each adjustment of the fixture, the state of charge of the lithium battery under test is in the empty state (0% SOC).

[0047] Example 4

[0048] The lithium battery under test was placed between the clamps. Before the cycle began, an initial pressure P0 = 0.2 MPa was applied to the lithium battery under test using the clamps, keeping the relative position between the clamps unchanged, and the cycle was repeated for 300 cycles. The clamps were then adjusted to apply a pressure P1 = 0.15 MPa to the lithium battery under test, keeping the relative position between the clamps unchanged, and the cycle was repeated for another 300 cycles. The entire cycle test consisted of 600 cycles. The lithium battery under test was a pouch lithium battery with a rated capacity of 30 Ah. The positive electrode active material was a nickel-cobalt-manganese ternary material, and the negative electrode active material was silicon-carbon material. During the entire cycle test, the lithium battery was charged and discharged using 1C (30A). The resting time between two adjacent charge / discharge cycles was 30 minutes. The voltage range for charging and discharging was 3.0–4.15 V. The capacity of the lithium battery under test was measured during the charge / discharge process, and the results are shown in Table 1. Before each clamp adjustment, the state of charge (SOC) of the lithium battery under test was 0%.

[0049] Comparative Example 1

[0050] The lithium battery under test was placed between the fixtures, and an initial pressure P0 = 1.0 MPa was applied to the battery using the fixtures. The relative position between the fixtures was kept constant, and the cycle was repeated for 600 cycles. The entire cycle test consisted of 600 cycles. The lithium battery under test was a pouch lithium battery with a rated capacity of 30 Ah. The positive electrode active material was a nickel-cobalt-manganese ternary material, and the negative electrode active material was a silicon-carbon material. During the entire cycle test, the lithium battery was charged and discharged using 1C (30A). The resting time between two adjacent charge and discharge cycles was 30 min. The voltage range for charge and discharge was 3.0–4.15 V. The capacity of the lithium battery under test was measured during the charge and discharge process, and the results are shown in Table 1.

[0051] Comparative Example 2

[0052] The lithium battery under test was placed between the fixtures, and an initial pressure P0 = 0.2 MPa was applied to the battery using the fixtures. The relative position between the fixtures was kept constant, and the cycle was repeated for 600 cycles. The entire cycle test consisted of 600 cycles. The lithium battery under test was a pouch lithium battery with a rated capacity of 30 Ah. The positive electrode active material was a nickel-cobalt-manganese ternary material, and the negative electrode active material was a silicon-carbon material. During the entire cycle test, the lithium battery was charged and discharged using 1C (30A). The resting time between two adjacent charge and discharge cycles was 30 min. The voltage range for charge and discharge was 3.0–4.15 V. The capacity of the lithium battery under test was measured during the charge and discharge process, and the results are shown in Table 1.

[0053] Comparative Example 3

[0054] Without applying pressure, the lithium battery under test was charged and discharged for 600 cycles. The lithium battery under test was a pouch lithium battery with a rated capacity of 30Ah. The positive electrode active material was a nickel-cobalt-manganese ternary material, and the negative electrode active material was a silicon-carbon material. During the entire cycle test, the lithium battery was charged and discharged at 1C (30A). The resting time between two adjacent charge and discharge cycles was 30 minutes. The voltage range of charge and discharge was 3.0 to 4.15V. The capacity of the lithium battery under test was measured during the charge and discharge process, and the results are shown in Table 1.

[0055] Comparative Example 4

[0056] The lithium battery under test was placed between fixtures, and an initial pressure P0 = 0.2 MPa was applied to the battery using the fixtures. During the cycling process, the relative position of the fixtures was adjusted to maintain a constant pressure of 0.2 MPa for 600 cycles. The lithium battery under test was a pouch lithium battery with a rated capacity of 30 Ah. The positive electrode active material was a nickel-cobalt-manganese ternary material, and the negative electrode active material was a silicon-carbon material. Throughout the cycle test, the lithium battery was charged and discharged using 1C (30A). The resting time between two adjacent charge and discharge cycles was 30 min, and the voltage range for charging and discharging was 3.0–4.15 V. The capacity of the lithium battery under test was measured during the charge and discharge process, and the results are shown in Table 1.

[0057] Table 1. Cycle performance of the lithium batteries tested in Examples 1-4 and Comparative Examples 1-4

[0058]

[0059] Table 1 shows the relationship between battery capacity retention capability and battery cycle number obtained in Examples 1-4 and Comparative Examples 1-4 of the present invention. The capacity retention rate is expressed as a percentage of the actual measured lithium battery discharge capacity after 600 cycles relative to the discharge capacity in the first cycle.

[0060] Comparing Example 1 and Comparative Example 1, as well as Example 3, Example 4 and Comparative Example 2, it is evident that reducing the pressure applied to the tested lithium battery during cycling can effectively improve the battery's cycle retention rate. Comparative Examples 1, 2, and 3 show that applying appropriate pressure to the lithium battery can improve cycle performance, but excessive pressure will degrade cycle performance. Therefore, the present invention's method of reducing the pressure applied to the lithium battery during cycling can effectively improve the capacity retention capability of the lithium battery during cycling.

[0061] Obviously, the above embodiments are merely examples for clear illustration and are not intended to limit the scope of the embodiments. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all embodiments here. However, obvious variations or modifications derived therefrom are still within the protection scope of this invention.

Claims

1. A method of improving the cycle performance of a lithium battery, characterized in that, The steps are as follows: Before the cycle starts, an initial pressure P0 is applied to the lithium battery using the clamp, the relative position between the clamps is kept unchanged, and the cycle is repeated for M times; The clamp is adjusted to apply pressure P1 to the lithium battery, the relative position between the clamps is kept unchanged, and the cycle is repeated for M times; Similarly, until the adjustment clamp, the lithium battery to apply pressure P N , the relative position between the holding clamp unchanged, the cycle M weeks. Said M respectively represents an integer between 0 and 1000; Said N represents the number of times of adjusting the clamp after applying the initial pressure P0 to the lithium battery using the clamp, and N≥1; P0≥ P1≥... ≥ P N ; P0, P1,..., P N each independently represents 0 to 2 MPa; Wherein, before each adjustment of the clamp, the state of charge of the lithium battery is consistent; each time the clamp is adjusted, the pressure change is a constant value, and the pressure change range is 0.01-0.1 MPa.

2. The method for improving the cycle performance of lithium batteries according to claim 1, characterized in that, Before each adjustment of the clamp, the lithium battery is in an empty state of 0% SOC.

3. The method for improving the cycling performance of lithium batteries of claim 1, wherein, The material of the clamp is one of an aluminum plate, a steel plate, and a rubber plate.

4. The method for improving the cycling performance of lithium batteries of claim 1, wherein, The positive electrode material of the lithium battery is one of a layered oxide positive electrode material, a polyanion positive electrode material, a spinel positive electrode material, and a lithium-rich ternary layered positive electrode material.

5. The method for improving the cycling performance of lithium batteries of claim 1, wherein, The negative electrode material of the lithium battery is one of natural graphite, artificial graphite, hard carbon, soft carbon, silicon-carbon, silicon, metallic lithium, and metallic tin.

6. The method for improving the cycling performance of lithium batteries of claim 1, wherein, The lithium battery is a soft-pack lithium battery or a square lithium battery.

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