An ultralow-temperature lithium ion battery and a processing method thereof

Abstract

The application discloses an ultralow-temperature lithium ion battery and a processing method thereof, and relates to the technical field of lithium ion batteries. The positive sheet of the lithium ion battery comprises a positive substrate, a positive material layer and an ultralow-temperature superconducting net framework layer; and the negative sheet comprises a negative substrate, a negative material layer and an ultralow-temperature superconducting net framework layer. The positive active material for preparing the positive material layer comprises lithium nickel cobalt manganese oxide, lithium manganate and lithium cobaltate; and the mass ratio of the lithium nickel cobalt manganese oxide, the lithium manganate and the lithium cobaltate is (5-20):(5-20):(60-90). The lithium ion battery prepared by the above scheme still has good charge-discharge performance in an ultralow-temperature environment through experiments.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to an ultra-low temperature lithium ion battery and a processing method thereof. BACKGROUND

[0002] Lithium ion batteries are widely used in mobile products such as mobile phones, computers and the like due to their high energy density and the like. However, most of the lithium ion batteries currently have poor low temperature performance, and often cannot work in low temperature environments. In addition, under low temperature conditions, the viscosity of the electrolyte increases, the flowability of lithium ions becomes poor, the internal polarization of the battery is intensified, and the safety risk is high. SUMMARY

[0003] The present application aims to overcome the deficiencies of the prior art and provide a lithium ion battery with good charge and discharge performance at ultra-low temperature and a processing method thereof.

[0004] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows:

[0005] A lithium ion battery, comprising a positive electrode sheet and a negative electrode sheet, the positive electrode sheet comprising a positive electrode substrate, a positive electrode material layer and an ultra-conductive mesh framework layer, the positive electrode material layer being prepared from a positive electrode slurry, the positive electrode slurry comprising a positive electrode active material, a binder A, a conductive agent A and a dispersing agent; the positive electrode active material comprising lithium nickel cobalt manganese oxide, lithium manganate and lithium cobaltate; the mass ratio of the lithium nickel cobalt manganese oxide, the lithium manganate and the lithium cobaltate being (5-20):(5-20):(60-90); the negative electrode sheet comprising a negative electrode substrate, a negative electrode material layer and an ultra-conductive mesh framework layer, the negative electrode material layer being prepared from a negative electrode slurry, the negative electrode slurry comprising a negative electrode active material, a binder B, a conductive agent B and a dispersing agent; the negative electrode active material being at least one of silicon powder, graphite, amorphous carbon powder and pitch powder; the conductive agent A and the conductive agent B being at least one of carbon nanotubes, graphene, VGCF and Super P, the conductive agent A and the conductive agent B being the same or different; the binder A and the binder B being the same or different.

[0006] The present application enhances the three-phase transmission of ions in the charge and discharge process under low temperature environment by preparing an ultra-conductive mesh framework layer on the positive / negative electrode material layer, reduces the transmission distance and reduces the low temperature polarization reaction. In addition, the present application selects lithium nickel cobalt manganese oxide, lithium manganate and lithium cobaltate as the positive electrode active material, which can balance the discharge efficiency and the conductivity, and improve the low temperature performance of the lithium ion battery.

[0007] Preferably, the negative active material is a mixture of graphite and amorphous carbon powder, and the mass ratio of the graphite to the amorphous carbon powder is (60-85):(15-40). The use of the above components as the negative active material can increase the discharge efficiency and power of the battery at low temperature.

[0008] Preferably, the conductive agent A is at least one of the following (1)-(3); the conductive agent B is a mixture of carbon nanotubes and a conductive agent C, and the conductive agent C is one of graphene, VGCF and Super P, and the mass ratio of the carbon nanotubes to the conductive agent C is (0.08-5):(0.1-7).

[0009] (1) a mixture of carbon nanotubes, graphene and VGCF, and the mass ratio of the carbon nanotubes to the graphene to the VGCF is (0.1-4.8):(0.002-1.45):(0.3-7);

[0010] (2) a mixture of carbon nanotubes and Super P, and the mass ratio of the carbon nanotubes to the Super P is (0.08-4.8):(0.3-6.8);

[0011] (3) a mixture of graphene and Super P, and the mass ratio of the graphene to the Super P is (0.002-3.5):(0.3-6.8).

[0012] The above selection of the components of the conductive agent A and the conductive agent B can reduce the interface impedance, lower the ion transmission impedance at low temperature, and reduce the potential difference caused by the decrease of activity at low temperature.

[0013] Preferably, the mass ratio of the positive active material, the binder A, the conductive agent A and the dispersant in the positive slurry is (80-98.5):(0.5-6.5):(0.5-10):(0.1-3). The mass ratio of the negative active material, the binder B, the conductive agent B and the dispersant in the negative slurry is (70-98):(0.5-6):(0.5-10):(0.1-3). The positive slurry and the negative slurry further contain a solvent, and the mass fraction of the solvent in the positive slurry is 20%-50%, and the mass fraction of the solvent in the negative slurry is 50%-65%.

[0014] The above limitation of the ratio of the components can ensure that the positive / negative active material layer has good electrical properties and good stability.

[0015] Preferably, the positive electrode substrate is composed of an aluminum foil and a carbon layer coated on the aluminum foil; the negative electrode is composed of a copper foil and a carbon layer coated on the copper foil; the carbon layer is prepared from a carbon coating slurry containing Super P, carbon nanotubes, graphene and a dispersing agent, the mass ratio of the Super P, carbon nanotubes and graphene being 1:(0.05-0.6):(0.05-0.6); the mass ratio of the carbon nanotubes and the dispersing agent being 1:(0.05-1). The application of the carbon layer on the metal current collector can greatly reduce the battery impedance, enhance the coating adhesion, improve the problem of easy oxidation of the metal current collector and improve the cycle life of the battery.

[0016] Preferably, the superconducting mesh framework layer is prepared from a superconducting mesh framework slurry containing Super P, VGCF, graphene and carbon nanotubes, the mass ratio of the Super P, VGCF, graphene and carbon nanotubes being 1:(0.3-0.8):(0.05-0.6):(0.05-0.6).

[0017] The structures of the Super P, VGCF and graphene are different, and one of them is used alone, and the interface impedance is relatively large. The three materials can reduce the three-phase interface impedance by being mixed in a certain ratio. The addition of the carbon nanotubes can solve the problem of conductive transmission between particles and make up for the shortage of solid particle surface contact. The multidirectional three-dimensional conductive mesh structure solves the problem of ion transmission at low temperature and reduces the potential difference caused by the reduction of activity at low temperature.

[0018] Preferably, the preparation method of the positive electrode sheet comprises the following steps: coating a carbon coating slurry on an aluminum foil, drying to obtain a positive electrode substrate; coating a positive electrode slurry on the positive electrode substrate, drying to obtain a positive electrode material layer; coating a superconducting mesh framework slurry on the positive electrode material layer, drying to obtain the positive electrode sheet.

[0019] The preparation method of the negative electrode sheet comprises the following steps: coating a carbon coating slurry on a copper foil, drying to obtain a negative electrode substrate; coating a negative electrode slurry on the negative electrode substrate, drying to obtain a negative electrode material layer; coating a superconducting mesh framework slurry on the negative electrode material layer, drying to obtain the negative electrode sheet.

[0020] Meanwhile, the application also discloses a preparation method of the lithium ion battery, which comprises the following steps: rolling and cutting the positive electrode sheet and the negative electrode sheet, winding or stacking the positive electrode sheet, the separator and the negative electrode sheet to prepare an electric core; welding a tab; placing the electric core into a shell for pre-packaging; baking the pre-packaged electric core; injecting an electrolyte by using a vacuum injection machine; packaging and forming to obtain the lithium ion battery.

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

[0022] The application improves the three-phase transmission capacity of ions in the process of charging and discharging in an ultra-low temperature environment by preparing a superconducting network skeleton layer; improves the discharging efficiency of the battery at low temperature by screening the positive and negative active materials; and reduces the potential difference caused by the reduction of activity at low temperature and reduces the interface impedance by screening the conductive agent. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Discharge curve of the lithium ion battery described in Example 1 and Example 3 at-40℃;

[0024] Figure 2 Discharge curve of the lithium ion battery described in Comparative Examples 1-3 at-40℃. DETAILED DESCRIPTION

[0025] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below in conjunction with the drawings and specific examples.

[0026] The materials used in the examples and comparative examples are as follows:

[0027] Solvent: N-methyl pyrrolidone (for the positive electrode), a mixture of deionized water and ethanol in a mass ratio of 9:1 (for the negative electrode);

[0028] Binder A: polyvinylidene fluoride;

[0029] Binder B: SBR;

[0030] Dispersant: SoterasTMMSI;

[0031] Conductive agent A: a compound of carbon nanotubes, graphene and VGCF in a mass ratio of 2.5:0.5:7;

[0032] Conductive agent B: a compound of carbon nanotubes and graphene in a mass ratio of 83:17;

[0033] Separator: polyethylene isolation film;

[0034] Electrolyte: a compound of ethyl acetate, vinyl carbonate, ethyl propionate and propyl acetate in a mass ratio of 10:2:3:2 as the solvent; the concentration of the additive lithium hexafluorophosphate is 1.2 mol / L, and the mass fraction of ethylene sulfite in the electrolyte is 4%.

[0035] Examples 1-3

[0036] The preparation method of the lithium ion battery described in the application, examples 1-3, is as follows, and the formulations of the carbon coating slurry, positive active material, negative active material and superconducting network skeleton slurry are shown in Tables 1-4:

[0037] (1) Preparation of positive electrode matrix and negative electrode matrix: double-sided coating of carbon coating paste on aluminum foil and copper foil, respectively, baking at 120°C to complete drying, single-sided coating thickness of 1 μm, surface density of 2 mg / cm 2 .

[0038] (2) Mix the positive electrode active material, conductive agent A, ball mill, then disperse with molecular sieve, dry, then mix with binder A, dispersant, solvent, stir to obtain semi-finished positive electrode paste; disperse the semi-finished positive electrode paste with a nano-homogenizing dispersing machine to obtain a positive electrode paste with uniform composition, the mass fraction of solvent in the positive electrode paste is 30%, the mass ratio of the positive electrode active material, binder A, conductive agent A, and dispersant is 90:4:4:2; coat the positive electrode paste on the positive electrode matrix (double-sided coating), dry to form a positive electrode material layer; single-sided coating thickness is 3 μm, surface density is 5 mg / cm 2 . Mix the negative electrode active material, conductive agent B, ball mill, then disperse with molecular sieve, dry, then mix with binder B, dispersant, solvent, stir to obtain semi-finished negative electrode paste; disperse the semi-finished negative electrode paste with a nano-homogenizing dispersing machine to obtain a negative electrode paste with uniform composition, the mass fraction of solvent in the negative electrode paste is 50%, the mass ratio of the negative electrode active material, binder B, conductive agent B, and dispersant is 80:5:10:2; coat the negative electrode paste on the negative electrode matrix (double-sided coating), dry to form a negative electrode material layer; single-sided coating thickness is 4 μm, surface density is 2.5 mg / cm 2 .

[0039] (3) Coat the superconducting mesh framework paste on the positive electrode material layer and the negative electrode material layer, respectively, dry to obtain positive electrode sheets and negative electrode sheets; the superconducting mesh framework paste is prepared from Super P, VGCF, graphene, carbon nanotubes, dispersant, binder, and solvent, the mass fraction of the dispersant is 2%, the mass fraction of the binder is 0.6%, and the mass fraction of the solvent is 97.4%. The coating surface density is 0.2 mg / cm 2

[0040] (4) Roll and cut the positive electrode sheets and negative electrode sheets, stack the positive electrode sheets, separators, and negative electrode sheets to form a battery cell; weld the tabs; place the battery cell in a housing for pre-packaging; bake the pre-packaged battery cell; inject electrolyte using a vacuum injection machine; package and form to obtain the lithium ion battery.

[0041] Table 1 Carbon coating paste (mass ratio)

[0042] Item Super P: carbon nanotube: graphene: dispersant: solvent Examples 1 to 3 7：1：1：0.4：95.5

[0043] Table 2 Positive electrode active material (mass ratio)

[0044] Item Lithium nickel cobalt manganese oxide: lithium manganese oxide: lithium cobalt oxide Example 1 5:5:90 Example 2 10:10:80 Example 3 20:20:60

[0045] Table 3 negative active material (mass ratio)

[0046] Item Graphite: amorphous carbon powder Examples 1 to 3 1：0.3

[0047] Table 4 superconducting mesh framework slurry (mass ratio)

[0048] Item Super P: VGCF: graphene: carbon nanotube Examples 1 to 3 1:0.5:0.3:0.3

[0049] Examples 4-5

[0050] The examples of the lithium ion battery described in the present application, examples 4-5 and example 2 only differ in the type of negative active material, in example 4, the negative active material is a compound of silicon powder and graphite, the mass ratio of silicon powder and graphite is 10:90; in example 5, the negative active material is only graphite.

[0051] Examples 6-8

[0052] The examples of the lithium ion battery described in the present application, examples 6-8 and example 2 only differ in the composition of the superconducting mesh framework slurry, wherein the mass fraction of the dispersant, the binder, and the solvent is the same as example 2, and the ratio of other components is shown in Table 5.

[0053] Table 5 superconducting mesh framework slurry (mass ratio)

[0054] Item Super P: VGCF: graphene: carbon nanotube Example 6 1:0.5:0.3:0 Example 7 1:0.5:0:0.3 Example 8 1:0:0.3:0.3

[0055] Comparative examples 1-3

[0056] Comparative examples 1-3 are lithium ion batteries, the lithium ion batteries and example 2 only differ in the type and ratio of active ingredients in the positive material, as shown in Table 6.

[0057] Table 6 positive active material (mass ratio)

[0058] Item Lithium nickel cobalt manganese oxide: lithium manganese oxide: lithium cobalt oxide Comparative Example 1 0:20:80 Comparative Example 2 20:0:80 Comparative Example 3 25:25:50

[0059] The performance test of examples 1-8 and comparative examples 1-3, after the battery is fully charged, respectively, in the test environment of-40℃, -60℃, -70℃, store for 16h, then test its discharge capacity and discharge efficiency in the corresponding environment at 5.5W power discharge to the cut-off voltage, the test results are shown in Tables 7-9.

[0060] Table 7

[0061] Item Discharge temperature °C Discharge capacity Ah Discharge efficiency % Example 1 -40℃ 6.756 92.3 Example 2 -40℃ 6.935 94.9 Example 3 -40℃ 6.895 94.7 Example 4 -40℃ 6.814 90.9 Example 5 -40℃ 6.538 89.9 Example 6 -40℃ 6.547 88.6 Example 7 -40℃ 6.478 87.9 Example 8 -40℃ 6.339 86.6 Comparative Example 1 -40℃ 5.299 69.5 Comparative Example 2 -40℃ 3.405 46.8 Comparative Example 3 -40℃ 2.457 33.6

[0062] Table 8

[0063]

[0064]

[0065] Table 9

[0066] Item Discharge temperature °C Discharge capacity Ah Discharge efficiency % Example 1 -70℃ 6.203 85.2 Example 2 -70℃ 6.379 87.3 Example 3 -70℃ 6.214 84.9 Example 4 -70℃ 6.199 82.7 Example 5 -70℃ 5.759 79.2 Example 6 -70℃ 5.726 77.5 Example 7 -70℃ 5.652 76.7 Example 8 -70℃ 5.182 70.8 Comparative Example 1 -70℃ 0.003 0.1 Comparative Example 2 -70℃ 0.001 0.1 Comparative Example 3 -70℃ 0.001 0.1

[0067] From Tables 7-9, it can be seen that the discharge efficiency of Comparative Examples 1-3 at -40℃ is less than 70%, and the discharge capacity at -60℃ and -70℃ is extremely low, and the lithium ion battery cannot be used.

[0068] The discharge efficiency of Examples 1-3 at -40℃ and -60℃ is more than 90%, and the discharge efficiency at -70℃ is also high, and the lithium ion battery can be used at ultra-low temperature. The test results of Comparative Example 2 and Examples 4-5 show that the discharge efficiency of Examples 4-5 is relatively low, which indicates that for the lithium ion battery system at ultra-low temperature, the use of the compound of graphite and amorphous carbon powder as the negative active material can obtain better electrical performance. The test results of Comparative Example 2 and Examples 6-8 show that when the composition of the superconducting network skeleton slurry contains SuperP, VGCF, graphene and carbon nanotube, and the mass ratio of the four components is 1:(0.3-0.8):(0.05-0.6):(0.05-0.6), the lithium ion battery has obviously better ultra-low temperature performance.

[0069] Figure 1 The discharge curve of the lithium ion battery of Example 1 and Example 3 at -40℃ is shown in FIG. 3. The main difference between Example 1 and Example 3 is the mass ratio of lithium manganate, lithium nickel cobalt manganate and lithium cobaltate in the positive electrode main material. The low-temperature discharge efficiency of Example 3 is slightly higher. Figure 2 The discharge curve of the lithium ion battery of Comparative Examples 1-3 at -40℃ is shown in FIG. 4. It can be seen from the figure that the low-temperature discharge performance of Comparative Examples 1-3 is extremely poor.

[0070] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the present application.

Claims

1. An ultralow temperature lithium-ion battery, characterized in that, The battery includes a positive electrode sheet and a negative electrode sheet, the positive electrode sheet comprises a positive electrode substrate, a positive electrode material layer and a superconducting mesh framework layer, the positive electrode material layer is prepared from a positive electrode slurry, the positive electrode slurry comprises a positive electrode active material, a binder A, a conductive agent A and a dispersant, the positive electrode active material comprises lithium nickel cobalt manganese oxide, lithium manganese oxide and lithium cobalt oxide, the mass ratio of the lithium nickel cobalt manganese oxide, the lithium manganese oxide and the lithium cobalt oxide is (5-20):(5-20):(60-90), the negative electrode sheet comprises a negative electrode substrate, a negative electrode material layer and a superconducting mesh framework layer, the negative electrode material layer is prepared from a negative electrode slurry, the negative electrode slurry comprises a negative electrode active material, a binder B, a conductive agent B and a dispersant, the negative electrode active material is at least one of silicon powder, graphite, amorphous carbon powder and pitch powder, the conductive agent A and the conductive agent B are at least one of carbon nanotubes, graphene, VGCF and Super P, and the conductive agent A and the conductive agent B are the same or different, and the binder A and the binder B are the same or different. The superconducting mesh framework layer is prepared from a superconducting mesh framework slurry, the superconducting mesh framework slurry comprises Super P, VGCF, graphene and carbon nanotubes, and the mass ratio of the Super P, the VGCF, the graphene and the carbon nanotubes is 1:(0.3-0.8):(0.05-0.6):(0.05-0.6). The superconducting mesh framework layer is prepared on the positive electrode material layer and the negative electrode material layer.

2. The ultra-low temperature lithium-ion battery of claim 1, wherein, The negative electrode active material is a compound of graphite and amorphous carbon powder, and the mass ratio of the graphite and the amorphous carbon powder is (60-85):(15-40).

3. The ultra-low temperature lithium-ion battery of claim 1, wherein, The conductive agent A is at least one of the compounds of (1)-(3) below, the conductive agent B is a compound of carbon nanotubes and a conductive agent C, the conductive agent C is one of graphene, VGCF and Super P, and the mass ratio of the carbon nanotubes and the conductive agent C is (0.08-5):(0.1-7). (1) a compound of carbon nanotubes, graphene and VGCF with a mass ratio of (0.1-4.8):(0.002-1.45):(0.3-7); (2) a compound of carbon nanotubes and Super P with a mass ratio of (0.08-4.8):(0.3-6.8); (3) a compound of graphene and Super P with a mass ratio of (0.002-3.5):(0.3-6.8).

4. The ultra-low temperature lithium-ion battery of claim 1, wherein, The mass ratio of the positive electrode active material, the binder A, the conductive agent A and the dispersant in the positive electrode slurry is (80-98.5):(0.5-6.5):(0.5-10):(0.1-3).

5. The ultra-low temperature lithium-ion battery of claim 1, wherein, The mass ratio of the negative electrode active material, the binder B, the conductive agent B and the dispersant in the negative electrode slurry is (70-98):(0.5-6):(0.5-10):(0.1-3).

6. The ultra-low temperature lithium-ion battery of claim 1, wherein, The positive electrode base is composed of an aluminum foil and a carbon layer coated on the aluminum foil; the negative electrode is composed of a copper foil and a carbon layer coated on the copper foil; the carbon layer is prepared from a carbon coating slurry containing Super P, carbon nanotubes, graphene and a dispersing agent, and the mass ratio of the Super P, carbon nanotubes and graphene is 1: (0.05-0.6): (0.05-0.6).

7. The ultra-low temperature lithium-ion battery of claim 6, wherein, The mass ratio of the carbon nanotubes and the dispersing agent is 1: (0.05-1).

8. The ultra-low temperature lithium-ion battery of claim 6, wherein, The preparation method of the positive electrode sheet comprises the following steps: coating the carbon coating slurry on the aluminum foil, drying to obtain a positive electrode base; coating a positive electrode slurry on the positive electrode base, drying to obtain a positive electrode material layer; coating a superconducting mesh framework slurry on the positive electrode material layer, drying to obtain the positive electrode sheet. The preparation method of the negative electrode sheet comprises the following steps: coating the carbon coating slurry on the copper foil, drying to obtain a negative electrode base; coating a negative electrode slurry on the negative electrode base, drying to obtain a negative electrode material layer; coating a superconducting mesh framework slurry on the negative electrode material layer, drying to obtain the negative electrode sheet.

9. A method of processing an ultra-low temperature lithium-ion battery as claimed in any one of claims 1 to 8, characterized in that, The method comprises the following steps: rolling and cutting the positive electrode sheet and the negative electrode sheet, winding or stacking the positive electrode sheet, a separator and the negative electrode sheet to form an electric core; welding a tab; placing the electric core into a shell for pre-packaging; The pre-packaged electric core is baked; an electrolyte is injected by using a vacuum injection machine; the electric core is packaged and formed to obtain the lithium ion battery. The pre-packaged electric core is baked; an electrolyte is injected by using a vacuum injection machine; the electric core is packaged and formed to obtain the lithium ion battery.

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