Method for improving insulation, corrosion resistance and wear resistance of aluminum shell for lithium-ion battery

Abstract

The present invention relates to the field of battery technology, and in particular, to a method for improving the insulation, corrosion resistance and wear resistance of an aluminum shell for a lithium-ion battery. The method for improving the insulation, corrosion resistance and wear resistance of an aluminum shell for a lithium-ion battery comprises the following steps: using an aluminum shell as an anode and stainless steel as a cathode, placing the aluminum shell in an electrolyte for micro-arc oxidation treatment; controlling the AC voltage of the micro-arc oxidation treatment to 645-650V and performing a constant voltage oxidation treatment, washing and drying the aluminum shell after the constant voltage oxidation treatment to obtain an aluminum shell containing an aluminum oxide film layer. The present invention prepares a layer of oxide film with small porosity, high surface flatness, controllable film composition, uniformity, insulation and wear resistance on the inner and outer surfaces of the aluminum alloy shell of a lithium-ion battery through specific electrical parameter settings.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a method for improving the insulation, corrosion resistance and wear resistance of an aluminum shell for a lithium-ion battery. Background Art

[0002] With the urgent need to increase the battery capacity density, aluminum alloy shells are used as shells for lithium-ion batteries due to their low density, high strength and thermal conductivity. However, the application of aluminum alloy shells also has many risks. For example, lithium ions can be embedded in aluminum alloys to form LiAl alloys, resulting in the pulverization of the shell material, reducing the mechanical strength of the aluminum shell and increasing the risk of failure and leakage. In addition, due to the addition of fluoride salts in lithium-ion batteries, HF is easily formed inside the battery, and HF can corrode the thinner passivation layer of the aluminum shell. Therefore, the aluminum alloy shell or pole group is generally treated in industry, such as making the shell conductive with the positive electrode to prevent lithium ions from being embedded in the shell, or wrapping an insulating film on the surface of the pole group and the surface of the aluminum shell to prevent short circuits between the negative electrode and the shell, and between the shells. In addition, at the module or PACK end of the lithium-ion battery, the damage of the outer insulating film and the friction corrosion of the shell due to the vibration and relative displacement of the battery cell will also increase the risk of failure of the aluminum alloy shell.

[0003] Micro-arc oxidation, also known as plasma electrolytic oxidation, in situ grows a ceramic oxide film with matrix elements as the main component and electrolyte elements as the auxiliary component on the surface of valve metals such as aluminum, magnesium, titanium and their alloys. The film has excellent insulation, wear resistance and corrosion resistance. Due to the influence of the growth mode of the micro-arc oxidation film, the traditional oxide film has the characteristics of porosity and high roughness. Under some specific working conditions, in order to ensure the corrosion resistance of the film, the film needs to be sealed for a second time, which greatly increases the cost of the technology. In addition, the porosity and large surface roughness also limit the application of this technology in the corrosion resistance and insulation protection treatment of lithium-ion battery shells. Because of the large porosity, there may be a risk of absorbing electrolyte, resulting in poor liquid in lithium-ion batteries; large surface roughness may cause damage to the diaphragm and the pole piece, causing greater safety hazards.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] An object of the present invention is to provide a method for improving the insulation, corrosion resistance and wear resistance of an aluminum shell for a lithium-ion battery, so as to solve the above-mentioned technical problems.

[0006] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0007] A method for improving the insulation, corrosion resistance and wear resistance of an aluminum shell for a lithium-ion battery comprises the following steps:

[0008] An aluminum shell is used as an anode and stainless steel is used as a cathode, and the aluminum shell is placed in an electrolyte for micro-arc oxidation treatment; the AC voltage of the micro-arc oxidation treatment is controlled to 645-650V and a constant voltage oxidation treatment is performed, and the aluminum shell after the constant voltage oxidation treatment is washed and dried to obtain an aluminum shell containing an aluminum oxide film layer.

[0009] In one embodiment, the electrolyte comprises sodium hexametaphosphate, sodium hydroxide and water; in the electrolyte, the concentration of sodium hexametaphosphate is 35-45 g / L, and the concentration of sodium hydroxide is 1.5-2.5 g / L.

[0010] In one embodiment, after the electrolyte is prepared, it is allowed to stand for 10 to 13 hours.

[0011] In one embodiment, the aluminum shell is pretreated before being placed in the electrolyte; the pretreatment includes: washing the aluminum shell and then applying glue to the upper edge of the aluminum shell.

[0012] In one embodiment, the constant pressure oxidation treatment is performed for 8 to 12 minutes.

[0013] In one embodiment, the AC voltage of the micro-arc oxidation treatment is controlled to be 645-650V at a voltage rise rate of 38-42V / s.

[0014] In one embodiment, during the constant-voltage oxidation treatment, the temperature of the electrolyte is controlled to be less than or equal to 35°C.

[0015] In one embodiment, the washing specifically comprises: soaking in water; the soaking time is 10 to 15 hours.

[0016] In one embodiment, the drying temperature is 90-105° C., and the drying time is 10-15 hours.

[0017] In one embodiment, the thickness of the aluminum oxide film layer is T μm, T = -0.42x 2 -0.63y 2 +1.55x+2.18y+0.36xy+10.56;

[0018] The aluminum oxide film layer has a cavity structure; the cavity diameter of the cavity structure is Dμm=-0.38x 2 -0.32y 2 +2x+0.63y+0.13xy+8.55;

[0019] Wherein, x represents the forward voltage conversion coefficient of the micro-arc oxidation equipment; y represents the negative voltage conversion coefficient of the micro-arc oxidation equipment; x is 1 to 5, and y is 0 to 5.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention prepares a uniform, insulating and wear-resistant oxide film with small porosity, high surface flatness and controllable film composition on the inner and outer surfaces of the aluminum alloy shell of the lithium-ion battery through specific electrical parameter settings; the film layer can avoid electrochemical corrosion caused by short circuit between the inside of the shell and the negative electrode, as well as chemical corrosion of the shell by the electrolyte; it can enhance the insulation and wear resistance between battery cells, thereby avoiding the risk of leakage caused by shell corrosion and friction and wear from the inside to the outside. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 The graphs of the current density and voltage changing with time during the plasma electrolytic oxidation treatment in Examples 1 to 5;

[0024] Figure 2 The cross-sectional scanning electron microscope images of the oxide films obtained in Examples 1 to 5;

[0025] Figure 3 The corrosion current density analysis diagram of the oxide film obtained in Examples 1 to 5;

[0026] Figure 4 This is a diagram showing the effect of different voltage parameters on film thickness and pore size. DETAILED DESCRIPTION

[0027] The embodiments of the present invention will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0028] A method for improving the insulation, corrosion resistance and wear resistance of an aluminum shell for a lithium-ion battery comprises the following steps:

[0029] An aluminum shell is used as an anode and stainless steel is used as a cathode, and the aluminum shell is placed in an electrolyte for micro-arc oxidation treatment; the AC voltage of the micro-arc oxidation treatment is controlled to 645-650V and a constant voltage oxidation treatment is performed, and the aluminum shell after the constant voltage oxidation treatment is washed and dried to obtain an aluminum shell containing an aluminum oxide film layer.

[0030] The present invention can effectively reduce the porosity of the micro-arc oxidation film through specific electrical parameters, thereby avoiding the sealing process, and can significantly reduce its surface roughness (a higher level of smoothness can be easily achieved through subsequent polishing), so that the micro-arc oxidation technology can be used for surface strengthening of aluminum shells of lithium-ion batteries.

[0031] The present invention uses micro-arc oxidation technology (using specific parameters) to form an in-situ film on the inner and outer layers of the aluminum alloy shell. The main component of the film is crystalline or amorphous aluminum oxide. On the one hand, the inner aluminum oxide film can effectively provide insulation and chemical corrosion resistance, thereby avoiding lithium corrosion (electrochemical corrosion) and HF corrosion (chemical corrosion) inside the shell; on the other hand, the oxide film on the outer layer of the aluminum shell can improve the insulation between the single cells and prevent the discharge phenomenon between the shells during high current charging. At the same time, due to the high hardness of the aluminum oxide film, it can effectively provide the friction and wear performance of the shell.

[0032] In one embodiment, the AC voltage of the micro-arc oxidation treatment is controlled to 645V, 646V, 647V, 648V, 650V, etc.

[0033] In one embodiment, the electrolyte includes sodium hexametaphosphate, sodium hydroxide and water; in the electrolyte, the concentration of sodium hexametaphosphate is 35-45g / L, and the concentration of sodium hydroxide is 1.5-2.5g / L. Compared with other types of electrolytes, the electrolyte of the present invention has a single film-forming component, mild discharge, and fast film growth rate. In one embodiment, in the electrolyte, the concentration of sodium hexametaphosphate is 35g / L, 36g / L, 37g / L, 40g / L, 43g / L, 45g / L, etc., and the concentration of sodium hydroxide is 1.5g / L, 1.6g / L, 1.8g / L, 2g / L, 2.2g / L, 2.5g / L, etc.

[0034] In one embodiment, after the electrolyte is prepared, it is allowed to stand for 10 to 13 hours, such as 12 hours.

[0035] In one embodiment, the aluminum shell is pretreated before being placed in the electrolyte; the pretreatment includes: washing the aluminum shell, and then applying glue to the upper edge of the aluminum shell. The aluminum shell of the present invention refers to an aluminum shell container with an opening, and the upper edge of the opening is subjected to glue. Washing the aluminum shell includes: ultrasonic cleaning in ethanol. After the treatment is completed, the glue layer on the upper edge of the shell is torn off, which does not affect the welding performance of the shell and the top cover.

[0036] In one embodiment, the constant voltage oxidation treatment time is 8 to 12 minutes, such as 8 minutes, 9 minutes, 10 minutes, 11 minutes or 12 minutes, etc. In one embodiment, the voltage rise rate of the AC voltage of the micro-arc oxidation treatment is controlled to 645 to 650V at 38 to 42V / s, such as 38V / s, 39V / s, 40V / s, 41V / s, 42V / s, etc. By appropriate constant voltage oxidation treatment time and voltage rise rate, it is ensured that an aluminum oxide film with excellent insulation, wear resistance and corrosion resistance is obtained on the surface of the aluminum shell.

[0037] In one embodiment, during the constant pressure oxidation treatment, the temperature of the electrolyte is controlled to be less than or equal to 35°C, such as 25-35°C, such as 25°C, 28°C, 30°C, 34°C, etc. by opening the cooling system.

[0038] In one embodiment, the washing specifically includes: soaking in water; the soaking time is 10 to 15 hours, such as 10 hours, 11 hours, 12 hours, 13 hours, 15 hours, etc., and the appropriate soaking time is used to ensure that there is no residual electrolyte in the membrane layer.

[0039] In one embodiment, the drying temperature is 90-105°C, such as 90°C, 95°C, 100°C, 105°C, etc., and the drying time is 10-15h, such as 10h, 11h, 12h, 13h or 15h, etc. The present invention ensures that the moisture in the film layer is completely removed by suitable drying temperature and time and negative pressure environment. In one embodiment, the soaked shell is dried in a vacuum oven.

[0040] In one embodiment, the micro-arc oxidation equipment system of the present invention is of the WH-1A type, with a current range of 0 to 50A, a working voltage controllable between -400 and +800V, and a maximum current of 40A.

[0041] In one embodiment, the ratio of the forward voltage to the negative voltage of the present invention is (1-5):(0-5), for example, 5:5, 5:4, 5:3, 5:2, 5:1, 5:0, 1:5, 2:5, 3:5, 4:5.

[0042] The micro-arc oxidation equipment system of the present invention has a button for controlling the ratio of forward voltage to negative voltage, which is a program control inherent in the equipment itself. By adjusting this button, the ratio of the forward voltage conversion coefficient x of the micro-arc oxidation equipment and the negative voltage conversion coefficient y of the micro-arc oxidation equipment can be correspondingly adjusted. In one embodiment, the ratio of x to y is (1-5): (0-5), for example, at least one of 5:5, 5:4, 5:3, 5:2, 5:1, 5:0, 1:5, 2:5, 3:5 and 4:5.

[0043] The oxide film prepared by the present invention has a single component; the oxide film has a lower porosity and a higher surface flatness, ensuring that the battery core will not be scratched inside; the oxide film has a suitable thickness to ensure the corrosion resistance and insulation of the inner shell film layer, as well as the insulation of the outer shell film layer.

[0044] In one embodiment, the thickness of the aluminum oxide film layer is T μm, T = -0.42x 2 -0.63y 2 +1.55x+2.18y+0.36xy+10.56.

[0045] The aluminum oxide film layer has a cavity structure; the cavity diameter of the cavity structure is Dμm, D=-0.38x 2 -0.32y 2 +2x+0.63y+0.13xy+8.55;

[0046] Wherein, x represents the forward voltage conversion coefficient of the micro-arc oxidation device; y represents the negative voltage conversion coefficient of the micro-arc oxidation device; x is 1 to 5, for example, 1, 2, 3, 4 or 5, and y is 0 to 5, for example, 0, 1, 2, 3, 4 or 5.

[0047] From the above formula, it can be seen that the pore size of the oxide film increases first and then decreases with the increase of positive x and y; the thickness of the oxide film increases first and then decreases with the increase of x and y. In order to ensure a smaller porosity and a larger film thickness, x is preferably 5 and y is 5.

[0048] The present invention can quickly find film preparation parameters suitable for certain working conditions by quantifying voltage parameters. The plasma electrolyte oxidation treatment with specific parameters is found through a formula, and a layer of oxide film with small porosity, high surface flatness, controllable film composition, uniformity, insulation and wear resistance is prepared on the inner and outer surfaces of the aluminum alloy shell of the lithium-ion battery. Thereby, an oxide film layer that can be used for lithium-ion batteries without the need for secondary sealing is achieved. The film layer can avoid electrochemical corrosion caused by short circuit between the inside of the shell and the negative electrode, as well as chemical corrosion of the shell by the electrolyte; on the other hand, it can enhance the insulation and wear resistance between the battery cells, thereby avoiding the risk of leakage caused by shell corrosion and friction and wear from the inside to the outside.

[0049] In one embodiment, the aluminum oxide film layer has a thickness of 10 to 20 μm, for example, 11 μm, 12 μm, 13 μm, 15 μm, 16 μm, 17 μm, 18 μm, 20 μm, etc.

[0050] The following is further explained in conjunction with specific embodiments.

[0051] Example 1

[0052] A method for improving the insulation, corrosion resistance and wear resistance of an aluminum shell for a lithium-ion battery comprises the following steps:

[0053] (1) placing the aluminum alloy shell in an ethanol solution for ultrasonic cleaning, and drying the cleaned aluminum shell in air;

[0054] (2) Apply glue to the upper edge of the dried aluminum shell (the welding part between the shell and the cover);

[0055] (3) using deionized water to prepare an electrolyte solution containing 40 g / L sodium hexametaphosphate and 2 g / L sodium hydroxide, and letting it stand for 12 hours;

[0056] (4) connecting the aluminum shell to the positive electrode fixture, immersing it in a stainless steel negative electrode tank filled with the above-mentioned electrolyte, and connecting the stainless steel tank to the negative electrode of the plasma electrolytic oxidation power supply, and connecting the shell to the positive electrode;

[0057] (5) adjusting the ratio of the forward voltage conversion coefficient x of the micro-arc oxidation device to the negative voltage conversion coefficient y of the micro-arc oxidation device to 5:1, using a voltage increase rate of 40.5 V / s to increase the plasma electrolytic oxidation power supply voltage to 648 V, and maintaining this voltage for 10 min, while turning on the cooling system to ensure that the electrolyte temperature is not higher than 35 ° C during the treatment;

[0058] (6) The treated shell is repeatedly washed in deionized water and soaked in deionized water for 12 hours to ensure that there is no residual electrolyte in the film layer; the soaked shell is baked in a vacuum oven at 100° C. for 12 hours to ensure that the moisture in the film layer is completely removed.

[0059] Example 2

[0060] A method for improving the insulation, corrosion resistance and wear resistance of an aluminum shell for a lithium-ion battery, wherein the ratio of a forward voltage conversion coefficient x of a micro-arc oxidation device to a negative voltage conversion coefficient y of the micro-arc oxidation device is adjusted to 5:3, and other conditions are the same as those in Example 1.

[0061] Example 3

[0062] A method for improving the insulation, corrosion resistance and wear resistance of an aluminum shell for a lithium-ion battery, wherein the ratio of a forward voltage conversion coefficient x of a micro-arc oxidation device to a negative voltage conversion coefficient y of the micro-arc oxidation device is adjusted to 5:5, and other conditions are the same as those in Example 1.

[0063] Example 4

[0064] A method for improving the insulation, corrosion resistance and wear resistance of an aluminum shell for a lithium-ion battery, wherein the ratio of a forward voltage conversion coefficient x of a micro-arc oxidation device to a negative voltage conversion coefficient y of the micro-arc oxidation device is adjusted to 3:5, and other conditions are the same as those in Example 1.

[0065] Example 5

[0066] A method for improving the insulation, corrosion resistance and wear resistance of an aluminum shell for a lithium-ion battery, wherein the ratio of a forward voltage conversion coefficient x of a micro-arc oxidation device to a negative voltage conversion coefficient y of the micro-arc oxidation device is adjusted to 1:5, and other conditions are the same as those in Example 1.

[0067] Experimental example

[0068] 1. The changes of current density and voltage over time during the plasma electrolytic oxidation treatment of Examples 1 to 5 are as follows: Figure 1 As shown in the figure, during the constant voltage treatment stage, the greater the discharge current density, the greater the discharge density or intensity. To achieve excellent oxide film performance, a thicker film layer and a smaller porosity are required. Therefore, the experimental scheme with a large current density and a low single discharge intensity will obtain better film performance. Figure 1 It can be seen that when the ratio of the forward voltage conversion coefficient x to the negative voltage conversion coefficient y of the micro-arc oxidation equipment is 5:5, the effect is better.

[0069] 2. The cross-sectional SEM images of the oxide films obtained in Examples 1 to 5 are as follows: Figure 2 As shown, Figure 2 (a) shows a cross-sectional SEM image of the oxide film obtained in Example 1. Figure 2 (b) shows a cross-sectional SEM image of the oxide film obtained in Example 2. Figure 2 (c) shows a cross-sectional SEM image of the oxide film obtained in Example 3. Figure 2 (d) shows a cross-sectional SEM image of the oxide film obtained in Example 4. Figure 2 (e) in the figure is a cross-sectional SEM image of the oxide film obtained in Example 5. Figure 2 It shows that the overall thickness of various oxide films is uniform, about 10 to 20 μm. The oxide film thickness decreases with the decrease of the forward voltage conversion coefficient. There are cavities generated by discharge in the oxide film. The SEM image shows that the size of these cavities decreases with the decrease of the forward voltage conversion coefficient and the increase of the negative voltage conversion coefficient. Therefore, an oxide film with a reasonable thickness and density will eventually show excellent corrosion resistance.

[0070] 3. The corrosion resistance of each oxide film is tested by potentiodynamic polarization curve. The results are as follows: Figure 3 As shown, consistent with the above analysis, when the ratio of the forward voltage conversion coefficient x to the negative voltage conversion coefficient y of the micro-arc oxidation equipment is 5:5, the corrosion current density of the obtained oxide film is the smallest, indicating that the corrosion resistance is the best.

[0071] 4. The influence of different voltage parameters on film thickness and pore size Figure 4 shown.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. Methods for improving the insulation, corrosion resistance and wear resistance of aluminum shells for lithium-ion batteries. It is characterized in that The following steps are involved: An aluminum shell is used as an anode and stainless steel is used as a cathode, and the aluminum shell is placed in an electrolyte for micro-arc oxidation treatment; an alternating voltage of the micro-arc oxidation treatment is controlled to 645-650V and a constant voltage oxidation treatment is performed, and the aluminum shell after the constant voltage oxidation treatment is washed and dried to obtain an aluminum shell containing an aluminum oxide film layer; The electrolyte is composed of sodium hexametaphosphate, sodium hydroxide and water; in the electrolyte, the concentration of sodium hexametaphosphate is 35-45 g / L, and the concentration of sodium hydroxide is 1.5-2.5 g / L; After the electrolyte is prepared, let it stand for 10 to 13 hours; The constant pressure oxidation treatment time is 8 to 12 minutes; The AC voltage of the micro-arc oxidation treatment is controlled to be 645-650V with a voltage rise rate of 38-42V / s.

2. The method for improving the insulation, corrosion resistance and wear resistance of the aluminum shell for lithium-ion batteries according to claim 1, It is characterized in that The aluminum shell is pretreated before being placed in the electrolyte; the pretreatment includes: washing the aluminum shell and then applying glue to the upper edge of the aluminum shell.

3. The method for improving the insulation, corrosion resistance and wear resistance of the aluminum shell for lithium-ion batteries according to claim 1, It is characterized in that During the constant-voltage oxidation treatment, the temperature of the electrolyte is controlled to be less than or equal to 35°C.

4. The method for improving the insulation, corrosion resistance and wear resistance of the aluminum shell for lithium-ion batteries according to claim 1, It is characterized in that The washing specifically includes: soaking in water; the soaking time is 10 to 15 hours.

5. The method for improving the insulation, corrosion resistance and wear resistance of the aluminum shell for lithium-ion batteries according to claim 1, It is characterized in that The drying temperature is 90-105° C., and the drying time is 10-15 hours.

6. The method for improving the insulation, corrosion resistance and wear resistance of the aluminum shell for lithium-ion batteries according to claim 1, It is characterized in that The thickness of the aluminum oxide film layer is T μm, T = -0.42x 2 -0.63y 2 +1.55x+2.18y+0.36xy+10.56; The aluminum oxide film layer has a cavity structure; the cavity diameter of the cavity structure is Dμm, D=-0.38x 2 -0.32y 2 +2x+0.63y+0.13xy+8.55; Wherein, x represents the forward voltage conversion coefficient of the micro-arc oxidation equipment; y represents the negative voltage conversion coefficient of the micro-arc oxidation equipment; x is 1 to 5, and y is 0 to 5.

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