High-performance lithium-manganese battery

Abstract

The invention provides a high-performance lithium-manganese battery, and belongs to the technical field of lithium batteries. Aiming at the problems of SEI film thickening, internal resistance increase and storage life influence caused by metal lithium / electrolyte interface side reaction when the lithium-manganese battery is stored for a long time, the invention provides a solution for constructing a graphite coating layer on the negative electrode side of the diaphragm. And during liquid injection and sealing, the metal lithium can be spontaneously embedded into the graphite layer to form the Li-LiC6 composite electrode. Compared with a compact SEI film on the surface of a metal lithium negative electrode, a stable and low-impedance SEI film can be generated on the surface of the loose and porous thin-layer Li-LiC6 composite electrode. The lithium-manganese battery using the graphite-coated diaphragm can realize lower initial resistance and battery internal resistance after long-term storage, and the storage life of the battery is remarkably prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly to a high-performance lithium manganese battery. Background Art

[0002] Primary lithium manganese batteries usually have a low self-discharge rate and a conventional storage life of more than 5 years. However, in recent years, with the expansion of long-cycle application scenarios such as Internet of Things devices and military equipment, end users have put forward higher requirements for the storage life of batteries, and some high-end application scenarios have put forward an ultra-long storage life of 10 years.

[0003] The storage life of the battery is mainly affected by the SEI film on the surface of metallic lithium. In lithium manganese batteries, elemental lithium can react chemically with certain components in the electrolyte to form an SEI film. On the one hand, this SEI film helps to inhibit the reaction between lithium and the electrolyte and extend the storage life of the battery; on the other hand, it will increase the internal resistance of the battery, and as the storage time increases, the SEI film gradually changes and the internal resistance continues to increase. After the internal resistance increases, the pulse load capacity of the battery decreases, and in severe cases, the battery may even fail to drive the load. Therefore, the evolution of the SEI film is the key factor restricting the storage life of the battery.

[0004] The growth of the SEI film in lithium manganese batteries is significantly affected by trace water and impurities (iron, sodium). These factors will exacerbate the interfacial side reactions, resulting in a continuous increase in the internal resistance during battery storage. To solve this problem, strict control of the raw materials and manufacturing process of the battery is required. The existing strategies are as follows: (1) Moisture control, for example: manganese powder is treated by high-temperature dehydration, which can not only reduce the lattice water in manganese dioxide, but also promote the transformation of part of the γ crystal form to the β crystal form, improving the material stability. (2) Impurity control, for example: lithium hydroxide can be used to replace sodium hydroxide in the production process of manganese dioxide to neutralize sulfuric acid in the electrolysis process, reducing the sodium content. (3) Additive optimization strategy, for example: adding lithium salts to the cathode formula or adding specific additives to the electrolyte can improve the SEI film structure and enhance its stability, thereby inhibiting the growth of internal resistance. (4) Pre-discharge treatment, for example: pre-discharging the batteries off the production line can also play a role in alleviating the increase in battery internal resistance and extending the battery life.

[0005] Although the above strategies can optimize the internal resistance performance of the battery after storage to a certain extent, the internal resistance of the battery will still increase significantly during long-term storage or high-temperature storage. In high-temperature resistant lithium manganese batteries, the method of using aluminum alloy to change the SEI film structure on the surface of metallic lithium can significantly improve the internal resistance performance of new batteries and batteries after high-temperature storage. However, this method has a relatively complex process, low production efficiency, and the formed lithium-aluminum alloy is prone to produce a small amount of powdered alloy, posing a potential risk of battery short circuit. Summary of the Invention

[0006] In view of this, the present invention provides a high-performance lithium manganese battery, which can significantly reduce the initial internal resistance of a new battery and the internal resistance of the battery after storage, thereby improving the storage life of the battery.

[0007] An embodiment of the present invention provides a high-performance lithium manganese battery, which is composed of a negative electrode lithium, a positive electrode sheet, an electrolyte, a graphite-coated separator, a current collector, a positive electrode case, and a negative electrode cover.

[0008] Preferably, the graphite-coated separator includes a separator and a graphite layer on the surface of the separator facing the negative electrode lithium side. After injecting the liquid, the graphite glue layer can spontaneously react with lithium to form a Li-LiC6 composite electrode.

[0009] Preferably, the graphite layer on the surface of the separator is coated by spraying or coating.

[0010] Preferably, the separators used include glass fiber separators, PP separators, and wire-wound separators.

[0011] Preferably, the area of the graphite layer is smaller than the blanking area of the separator.

[0012] Preferably, the coating shape of the graphite layer includes circular and square.

[0013] Preferably, the thickness of the dried graphite layer is 0.001 - 0.5 mm.

[0014] Preferably, the graphite carrier used for coating is graphite emulsion, and the mass fraction of graphite is 0.001% - 45%.

[0015] To improve the long-term storage life of the lithium manganese battery, the present invention adopts a process of coating graphite conductive glue on the separator to form a thin graphite layer. When the battery is encapsulated, the graphite layer on the surface of the separator faces the metallic lithium. According to the conventional encapsulation process of lithium manganese batteries, after injecting the liquid and sealing, when lithium is in close contact with the graphite layer with the electrolyte, an intercalation reaction can occur spontaneously, generating a golden-yellow LiC6 thin layer, and finally forming a Li-LiC6 thin layer composite electrode. Although LiC6 can also react with the electrolyte to form a SEI film, since graphite is a powder electrode, the impedance of the SEI film formed on its surface is much smaller than that of the dense SEI film on the surface of metallic lithium. Therefore, the lithium manganese battery prepared with this composite electrode shows a smaller internal resistance than ordinary batteries, and the internal resistance of the battery after high-temperature storage shows the same pattern. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic structural diagram of a lithium manganese battery using a graphite-coated separator;

[0017] Figure 2 It is a schematic diagram of the graphite layer on the surface of the separator, showing the relationship between the area of the graphite layer and the blanking area of the separator;

[0018] Figure 3Internal resistance diagram after high-temperature storage for the control group;

[0019] Figure 4 Internal resistance diagram after high-temperature storage for Example 1;

[0020] Figure 5 Internal resistance diagram after high-temperature storage for Example 2;

[0021] Figure 6 Internal resistance diagram after high-temperature storage for Example 3;

[0022] Figure 7 Internal resistance diagram after high-temperature storage for Example 4. Detailed implementation manners

[0023] The following is combined with the drawings and examples to further illustrate the present invention, rather than limiting the present invention.

[0024] Refer to Figures 1 to 2 , an embodiment of the present invention provides a high-performance lithium manganese battery, which is composed of a negative electrode lithium, a positive electrode sheet, an electrolyte, a graphite-coated separator, a current collector, a positive electrode case, and a negative electrode cover.

[0025] In one embodiment, the graphite-coated separator includes a separator and a graphite layer on the surface of the separator facing the negative electrode lithium side. After injecting the liquid, the graphite glue layer can spontaneously react with lithium to form a Li-LiC6 composite electrode.

[0026] In one embodiment, the graphite layer on the surface of the separator is coated by spraying or coating.

[0027] In one embodiment, the separator used includes but is not limited to a glass fiber separator, a PP separator, and a wire-wound separator.

[0028] In one embodiment, the area of the graphite layer is smaller than the blanking area of the separator to avoid short circuits caused by the graphite layer.

[0029] In one embodiment, the coating shape of the graphite layer is not limited, and specifically may include a circular shape and a square shape.

[0030] In one embodiment, the thickness of the dried graphite layer is 0.001 - 0.5 mm.

[0031] In one embodiment, the graphite carrier used during coating is a graphite emulsion, and the mass fraction of graphite is 0.001% - 45%.

[0032] The following is verified through specific examples as follows:

[0033] Control group

[0034] Encapsulate CR1216 lithium manganese batteries with fiberglass diaphragms without a coated graphite layer (diaphragm thickness 0.18 mm). The negative electrode is metallic lithium, the positive active material is manganese dioxide, and the electrolyte is the commonly used electrolyte for lithium manganese button batteries. Test the internal resistance of the batteries when newly charged and after storing at 85 °C for 15 days.

[0035] As Figure 3 shown, the average internal resistance of the newly charged batteries with the diaphragm without a graphite layer is 26.01 Ω. The average internal resistance of this batch of batteries after storing at 85 °C for 15 days is 45.49 Ω, and the upper limit of the internal resistance of the batteries after storing at 85 °C is close to 60 Ω. According to the Arrhenius equivalent aging empirical formula, storing at 85 °C for 15 days is equivalent to storing at room temperature for 3 years.

[0036] Example 1

[0037] Adopt the process of first dripping glue and then moving and head-on rolling to evenly coat a graphite glue with a mass fraction (graphite) of 18% on one side of the fiberglass diaphragm (thickness 0.25 mm), and the coating diameter is 5 mm. After the graphite layer is cured, it is punched and assembled into a CR1216 battery, with the graphite layer of the diaphragm facing the negative lithium. Test the internal resistance of the batteries when newly charged and after storing at 85 °C for 15 days.

[0038] As Figure 4 shown, the average internal resistance of the newly charged batteries in Example 1 is 11.26 Ω, which is lower than the average internal resistance of the newly charged batteries in the control group (26.01 Ω), indicating that coating the graphite layer on the negative electrode side of the diaphragm can reduce the internal resistance of the newly charged batteries; the internal resistance of the batteries in Example 1 gradually increases with the extension of the storage time at 85 °C. When stored for 15 days, the average internal resistance of the batteries is 24.86 Ω, which is much lower than the average internal resistance of the batteries in the control group after storing at 85 °C for 15 days (45.49 Ω), and the maximum internal resistance of this batch of batteries after storage is lower than the minimum internal resistance of the batteries in the control group after storage, indicating that coating the graphite layer on the negative electrode side of the diaphragm can reduce the internal resistance during long-term storage of the batteries.

[0039] Example 2

[0040] Adopt the process of first dripping glue and then moving and head-on rolling to evenly coat a graphite glue with a mass fraction (graphite) of 18% on one side of the punched fiberglass diaphragm (thickness 0.18 mm), and the coating area does not exceed the punched diaphragm sheet. After the graphite layer is cured, it is assembled into a CR1216 battery, with the graphite layer of the diaphragm facing the negative lithium. Test the internal resistance of the batteries when newly charged and after storing at 85 °C for 15 days.

[0041] As Figure 5As shown, the average internal resistance of the new battery in Example 2 is 8.76 Ω, which is much lower than that of the new battery in the control group (26.01 Ω), indicating that coating the graphite layer on the negative side of the separator can reduce the internal resistance of the new battery; the internal resistance of the battery in Example 2 gradually increases with the extension of storage time at 85 °C. The average internal resistance of the battery after 15 days of storage is 15.81 Ω, which is much lower than that of the battery in the control group stored at 85 °C for 15 days (45.49 Ω), and the maximum internal resistance of this batch of batteries after storage does not exceed 20 Ω, indicating that coating the graphite layer on the negative side of the separator can reduce the internal resistance during long-term storage of the battery.

[0042] Example 3

[0043] The graphite paste with a mass fraction (graphite) of 30% was evenly coated on one side of the punched fiberglass separator (thickness 0.18 mm) by adopting the process of first dripping glue and then moving and head-rolling. The coating area does not exceed the punched separator sheet. After the graphite layer is cured, it is assembled into a CR1216 battery. The graphite layer of the separator faces the negative lithium, and the internal resistances of the new battery and the battery after 15 days of storage at 85 °C are respectively tested.

[0044] As Figure 6 shown, the average internal resistance of the new battery in Example 3 is 17.7 Ω, lower than that of the new battery in the control group (26.01 Ω), indicating that coating the graphite layer on the negative side of the separator can reduce the internal resistance of the new battery; the internal resistance of the battery in Example 3 gradually increases with the extension of storage time at 85 °C. The average internal resistance of the battery after 15 days of storage is 22.03 Ω, which is much lower than that of the battery in the control group stored at 85 °C for 15 days (45.49 Ω), indicating that coating the graphite layer on the negative side of the separator can reduce the internal resistance during long-term storage of the battery. However, the average internal resistance of the new battery and the average internal resistance after 15 days of storage at 85 °C in Example 3 are both higher than the corresponding values in Example 2, indicating that the graphite concentration in the graphite paste has an impact on the increase of the internal resistance of the new battery and the battery during storage.

[0045] Example 4

[0046] The graphite paste with a mass fraction (graphite) of 18% was evenly coated on one side of the punched PP separator (thickness 0.25 mm) by adopting the process of first dripping glue and then moving and head-rolling. The coating area does not exceed the punched separator sheet. After the graphite layer is cured at high temperature, it is assembled into a CR1216 battery. The graphite layer of the separator faces the negative lithium, and the internal resistances of the new battery and the battery stored at 60 °C for 66 days are respectively tested.

[0047] As Figure 7As shown, the average internal resistance of the new battery in Example 4 is 14.37 Ω, which is lower than that of the new battery in the control group (26.01 Ω), indicating that coating the graphite layer on the negative side of the separator can reduce the internal resistance of the new battery; the internal resistance of the battery in Example 4 increases slightly with the extension of storage time at 60 °C. The average internal resistance of the battery is 21.04 Ω after 66 days of storage, which is much lower than the average internal resistance of the battery in the control group stored at 85 °C for 66 days (45.49 Ω), indicating that coating the graphite layer on the negative side of the separator can reduce the internal resistance of the battery during long-term storage.

[0048] The above is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and scope of the present invention are included in the protection scope of the present invention.

Claims

1. A high-performance lithium-manganese battery, characterized in that, It consists of a negative electrode lithium, a positive electrode sheet, an electrolyte, a graphite-coated separator, a current collector, a positive electrode case, and a negative electrode cover.

2. The high-performance lithium manganese battery according to claim 1, characterized in that, The graphite-coated separator includes a separator and a graphite layer on the surface of the separator facing the negative electrode lithium side. After injecting the electrolyte, the graphite glue layer can spontaneously react with lithium to form a Li-LiC6 composite electrode.

3. A high-performance lithium manganese battery according to claim 2, characterized in that, The graphite layer on the surface of the separator is coated by spraying or coating.

4. A high-performance lithium manganese battery according to claim 2, characterized in that, The separators used include glass fiber separators, PP separators, and wire-wound separators.

5. A high-performance lithium manganese battery according to claim 2, characterized in that, The area of the graphite layer is smaller than the blanking area of the separator.

6. A high-performance lithium manganese battery according to claim 2, characterized in that, The coating shape of the graphite layer includes circular and square.

7. A high-performance lithium manganese battery according to claim 2, characterized in that, The thickness of the dried graphite layer is 0.001 - 0.5 mm.

8. A high-performance lithium manganese battery according to claim 2, characterized in that, The graphite carrier used for coating is a graphite emulsion, and the mass fraction of graphite is 0.001% - 45%.

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