Lithium ion battery formation quality evaluation device and evaluation method

Abstract

The invention belongs to the field of batteries, and particularly relates to a lithium ion battery formation quality evaluation device and an evaluation method. The lithium ion battery formation quality evaluation device comprises a sample test bin and a cover body arranged on the sample test bin, the sample testing bin is provided with a liquid discharge valve and a liquid inlet valve; and the sample testing cabin is used for accommodating a battery pole group to be evaluated. According to the lithium ion battery formation quality evaluation device and the evaluation method provided by the invention, the battery formation is evaluated by calculating the coulombic efficiency of charging and discharging after the solvent with poor graphite cathode compatibility is added, and the method can be used for quickly evaluating the formation by using the simple device and reagent.

Description

Technical Field

[0001] The invention belongs to the field of batteries, and in particular relates to a lithium ion battery formation quality evaluation device and an evaluation method. Background Art

[0002] In recent years, new energy vehicles and distributed energy have developed rapidly, and the energy storage industry has also ushered in a period of rapid growth. Electrochemical batteries represented by lithium-ion batteries have been widely used in the electric vehicle and energy storage markets due to their superior characteristics such as high energy density, no memory effect, and no pollution. Electrochemical energy storage also puts forward higher requirements on battery safety, cost, and consistency. Due to its excellent electrochemical performance, lithium-ion batteries have become the mainstream development direction in the field of electrochemical energy storage. The requirements for lithium-ion batteries in energy storage conditions can be summarized as long life, high safety, and low cost.

[0003] In the production process of lithium-ion batteries, formation is an important process, and the quality of formation directly affects the performance of the battery. The formation process includes electrolyte infiltration, battery interface activation, battery side reactions and solid electrolyte interface layer formation. The formation method has a great impact on battery performance.

[0004] Although the traditional small current formation process can obtain a better positive and negative electrode interface, its process is complicated, time-consuming and has high production costs. How to shorten the formation time and save production costs is also the direction of continuous research in lithium battery technology. Different formation methods have both electrical performance and safety impacts. However, at present, both long-term small current formation and high-voltage, high-temperature and large current formation methods have process and cost problems. Exploring suitable formation methods is of great significance to optimizing the lithium-ion battery production process and improving battery performance. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a lithium ion battery formation quality evaluation device and evaluation method.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A lithium-ion battery formation quality evaluation device comprises a sample test chamber and a cover body arranged on the sample test chamber; the sample test chamber is provided with a liquid discharge valve and a liquid inlet valve; the sample test chamber is used to accommodate a battery electrode group to be evaluated.

[0008] The sample test chamber is provided with a pole group fixture connected to the pole ear of the battery pole group to be evaluated; the pole group fixture is connected to the external pole ear arranged outside the sample test chamber to charge and discharge the battery pole group to be evaluated.

[0009] A sealing ring is arranged between the cover body and the sample testing chamber.

[0010] Preferably, screw holes are correspondingly provided on the sample testing chamber and the cover body; the sample testing chamber and the cover body are connected by bolts.

[0011] The present invention also includes a lithium ion battery formation quality evaluation method, which uses the evaluation device.

[0012] The steps include:

[0013] 1) Place the battery electrode group to be evaluated into the sample test chamber, connect the electrode tabs of the battery electrode group to be evaluated to the electrode tab fixture, add electrolyte, and cover the cover body for sealing;

[0014] 2) Forming the battery electrode group to be evaluated according to a predetermined formation plan;

[0015] 3) Add the solvent with poor compatibility with graphite into the sample test chamber through the liquid inlet valve, and discharge an equal amount of electrolyte through the liquid discharge valve;

[0016] 4) After standing still, charge and discharge the battery and determine the quality of the battery by using the Coulomb efficiency.

[0017] In step 3), the solvent with poor compatibility with graphite is a highly polar or small molecule solvent; preferably, the solvent with poor compatibility with graphite is one of propylene carbonate, ethylene glycol dimethyl ether, or dimethyl sulfoxide, or a mixture thereof.

[0018] In step 3), the injection amount of the solvent with poor graphite compatibility is 1 / 5-1 / 20 of the injection amount of the electrolyte; preferably 1 / 10.

[0019] The standing time in step 4) is 12-48 hours, preferably 24 hours.

[0020] In step 2), different formation schemes are used to form the battery electrode group to be evaluated. In step 4), the coulombic efficiency of different formation schemes is calculated. The higher the coulombic efficiency, the better the formation quality; the lower the coulombic efficiency, the worse the formation quality.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] After the formation, the present application adds a solvent with poor compatibility with the graphite negative electrode, and its molecules are easily co-embedded with lithium ions in the graphite interlayer, causing the structural delamination of the graphite material, thereby affecting the performance and life of the battery. The battery with good formation effect is more stable because its negative electrode is less likely to react with the solvent with poor compatibility with the graphite negative electrode and be destroyed. When the negative electrode reacts with the solvent with poor compatibility with the graphite negative electrode, it is manifested as an increase in charging capacity and a decrease in discharge capacity during the charge and discharge process, that is, low coulomb efficiency. In view of this, the present application provides a lithium ion battery formation quality evaluation device and evaluation method, which evaluates the battery formation by calculating the coulomb efficiency of charging and discharging after adding a solvent with poor compatibility with the graphite negative electrode. The method uses simple devices and reagents and can quickly evaluate the formation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the structure of a lithium-ion battery formation quality evaluation device according to an embodiment of the present invention;

[0024] Figure 2 Graph showing test results of conventional battery cycle tests obtained according to different formation schemes in embodiments of the present invention. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and the best embodiments.

[0026] Figure 1 A lithium-ion battery formation quality evaluation device is shown, comprising a sample test chamber 1 and a cover 3 arranged on the sample test chamber; the sample test chamber is provided with a drain valve 8 and a liquid inlet valve 7; the sample test chamber is used to accommodate a battery electrode group 9 to be evaluated.

[0027] The sample test chamber is provided with a pole group fixture 6 connected to the pole lug of the battery pole group 9 to be evaluated; the pole group fixture 6 is connected to the outer pole lug 5 arranged outside the sample test chamber to charge and discharge the battery pole group 9 to be evaluated.

[0028] A sealing ring 2 is provided between the cover 3 and the sample test chamber 1. Screw holes are provided on the sample test chamber and the cover 3 correspondingly; the sample test chamber and the cover are connected by bolts 4.

[0029] A lithium-ion battery formation quality evaluation method, using the evaluation device, comprises the following steps:

[0030] 1) Place the electrode group 9 of the battery to be evaluated (hereinafter referred to as the electrode group) into the sample test chamber 1, connect the electrode tabs of the electrode group 9 of the battery to be evaluated to the electrode tab fixture 6, add electrolyte, and cover the cover 3 for sealing;

[0031] 2) forming the battery electrode group 9 to be evaluated according to a predetermined formation plan;

[0032] 3) Add the solvent with poor compatibility with graphite into the sample test chamber 1 through the liquid inlet valve 7, and discharge an equal amount of electrolyte through the liquid discharge valve 8; the solvent with poor compatibility with graphite is a strong polar or small molecule solvent; preferably, the solvent with poor compatibility with graphite is one of propylene carbonate, ethylene glycol dimethyl ether, or dimethyl sulfoxide or a mixture thereof. The injection amount of the solvent with poor compatibility with graphite is 1 / 5-1 / 20 of the injection amount of the electrolyte, specifically 1 / 5, 1 / 10 or 1 / 20; preferably 1 / 10.

[0033] 4) After standing still, charge and discharge are performed, and the quality of the formation is judged by coulomb efficiency. The standing time is 12-48 hours; specifically, it can be 12 hours, 24 hours, 48 ​​hours; preferably, 24 hours.

[0034] The method can use different formation schemes to form the battery electrode group to be evaluated in step 2), and calculate the coulombic efficiency of different formation schemes in step 4). The higher the coulombic efficiency, the better the formation quality; the lower the coulombic efficiency, the worse the formation quality.

[0035] The present invention is described in detail below by taking a battery as an example and combining with the accompanying drawings. In this embodiment, the battery electrode group to be evaluated is a lithium-ion experimental battery with a capacity of 4.0Ah and an electrolyte injection volume of 7.2g. The battery test equipment is a conventional charge and discharge instrument, and the equipment used in this embodiment is an Arbin BT2000 charge and discharge system.

[0036] A lithium-ion battery formation quality evaluation method, using the evaluation device, comprises the following steps:

[0037] 1): Add the electrode groups of two batteries into the sample test chamber 1 and assemble them. Inject the electrolyte according to the injection amount of 7.2g per battery.

[0038] 2): The two electrode groups are formed according to the two schemes shown in Table 1.

[0039] Table 1

[0040]

[0041] 3): Add 0.7 g of propylene carbonate PC through the liquid inlet valve, release approximately the same amount of electrolyte through the liquid discharge valve, and let it stand for 24 hours.

[0042] 4): The two batteries were cycled according to the following process: 0.5C = 2.0A constant current charging until the voltage reached 4.2V, then charged at 4.2V constant voltage until the current dropped to 0.05C = 0.2A, and discharged at 1C = 4.0A until the voltage reached 2.5V. The charge and discharge coulomb efficiency was calculated as shown in Table 2.

[0043] Table 2

[0044] Charging capacity Discharge capacity Coulomb efficiency Solution 1 3.9516 3.9477 99.902％ Solution 2 3.9590 3.9387 99.487％

[0045] 5): The coulombic efficiency of the battery in Scheme 1 is greater than that of the battery in Scheme 2, and the cycle performance of the battery in Scheme 1 is better than that of the battery in Scheme 2. The formation effect is better.

[0046] Figure 2 The test results of two batteries from the same batch without PC medium were put into the conventional cycle test. The test method of the conventional cycle test is: at room temperature, 0.5C = 2.0A constant current charging until the voltage reaches 4.2V, then charging at 4.2V constant voltage until the current drops to 0.05C = 0.2A, and discharging at 1C = 4.0A until the voltage reaches 2.5V. This charging and discharging is repeated. Figure 2 The results show that at the same 700 cycles, the capacity retention rates of the two types of batteries are 86% and 79% respectively, that is, Scheme 1 battery > Scheme 2 battery, which is consistent with the test results using PC medium in Table 1.

[0047] In addition, after experiments, the PC in the embodiment was replaced with ethylene glycol dimethyl ether and / or dimethyl sulfoxide. According to the calculated coulombic efficiency, the formation quality can also be evaluated, and it is verified that the evaluation result is more accurate.

[0048] In summary, after the formation, the present application adds a solvent with poor compatibility with the graphite negative electrode, and its molecules are easily co-embedded with lithium ions in the graphite interlayer, causing the structural delamination of the graphite material, thereby affecting the performance and life of the battery. The battery with good formation effect is more difficult to be destroyed by the reaction of the negative electrode with the solvent with poor compatibility with the graphite negative electrode, and is more stable. When the negative electrode reacts with the solvent with poor compatibility with the graphite negative electrode, it is manifested as an increase in charging capacity and a decrease in discharge capacity during the charge and discharge process, that is, low coulomb efficiency. In view of this, the present application provides a lithium ion battery formation quality evaluation device and evaluation method, by calculating the coulomb efficiency of charging and discharging after adding a solvent with poor compatibility with the graphite negative electrode, the battery formation is evaluated, and the method uses a simple device and reagent, and can quickly evaluate the formation.

[0049] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A lithium-ion battery formation quality evaluation device, characterized in that: It comprises a sample test chamber and a cover body arranged on the sample test chamber; the sample test chamber is provided with a liquid discharge valve and a liquid inlet valve; the sample test chamber is used to accommodate a battery electrode group to be evaluated.

2. The lithium-ion battery formation quality evaluation device according to claim 1, characterized in that: The sample test chamber is provided with a pole group fixture connected to the pole ear of the battery pole group to be evaluated; the pole group fixture is connected to the external pole ear arranged outside the sample test chamber to charge and discharge the battery pole group to be evaluated.

3. The lithium-ion battery formation quality evaluation device according to claim 1, characterized in that: A sealing ring is arranged between the cover body and the sample testing chamber.

4. The lithium-ion battery formation quality evaluation device according to claim 1, characterized in that: The sample test chamber and the cover body are correspondingly provided with screw holes; the sample test chamber and the cover body are connected by bolts.

5. A lithium ion battery formation quality evaluation method, characterized in that: Use the evaluation device described in any one of claims 1 to 4.

6. The lithium-ion battery formation quality evaluation method according to claim 5, characterized in that: The steps include: 1) Place the battery electrode group to be evaluated into the sample test chamber, connect the electrode tabs of the battery electrode group to be evaluated to the electrode tab fixture, add electrolyte, and cover the cover body for sealing; 2) Forming the battery electrode group to be evaluated according to a predetermined formation plan; 3) Add the solvent with poor compatibility with graphite into the sample test chamber through the liquid inlet valve, and discharge an equal amount of electrolyte through the liquid discharge valve; 4) After standing still, charge and discharge the battery and determine the quality of the battery by using the Coulomb efficiency.

7. The lithium ion battery formation quality evaluation method according to claim 6, characterized in that: In step 3), the solvent with poor compatibility with graphite is a highly polar or small molecule solvent; preferably, the solvent with poor compatibility with graphite is one of propylene carbonate, ethylene glycol dimethyl ether, or dimethyl sulfoxide, or a mixture thereof.

8. The lithium-ion battery formation quality evaluation method according to claim 6, characterized in that: In step 3), the injection amount of the solvent with poor graphite compatibility is 1 / 5-1 / 20 of the injection amount of the electrolyte; preferably 1 / 10.

9. The lithium-ion battery formation quality evaluation method according to claim 6, characterized in that: The standing time in step 4) is 12-48 hours, preferably 24 hours.

10. The lithium ion battery formation quality evaluation method according to claim 6, characterized in that: In step 2), different formation schemes are used to form the battery electrode group to be evaluated. In step 4), the coulombic efficiency of different formation schemes is calculated. The higher the coulombic efficiency, the better the formation quality; the lower the coulombic efficiency, the worse the formation quality.

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