High-energy-density lithium ion battery and preparation method thereof

Abstract

The invention discloses a high-energy-density lithium ion battery and a preparation method thereof.The high-energy-density lithium ion battery comprises high-nickel ternary positive electrode slurry, an electrode plate, electrolyte and silicon-carbon composite negative electrode slurry, the high-nickel ternary positive electrode slurry comprises a positive electrode active material, a positive electrode conductive agent and a positive electrode binder, and the silicon-carbon composite negative electrode slurry comprises nanometer silicon particles, graphene and a negative electrode binder; the method comprises the following steps: step 1, preparing a positive electrode material, step 2, preparing a negative electrode material, step 3, coating and drying, step 4, rolling and slitting, step 5, assembling and injecting liquid, and step 6, forming and packaging. The graphene and the carbon black cooperatively construct a three-dimensional conductive network, the contact resistance is reduced, the rate capability is improved, meanwhile, the graphene is used as a buffer layer between an electrolyte and an electrode, the interface impedance is effectively reduced, lithium dendrite growth is inhibited, the graphene is used as the buffer layer, the volume expansion of silicon is inhibited, and the lithium ion battery performance is improved. The problems of short cycle life caused by volume expansion of a silicon-based negative electrode and capacity fading caused by interface side reaction of a high-nickel positive electrode are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a high energy density lithium-ion battery and a preparation method thereof. Background Art

[0002] Deep-sea special batteries are high-performance power systems designed for extreme marine environments, and need to have characteristics such as high pressure resistance, corrosion resistance, long life, and high energy density to meet the needs of deep-sea exploration, equipment power supply, and scientific research. The core challenge lies in adapting to the harsh conditions of high pressure in the deep sea (such as the pressure in the ten-thousand-meter deep sea exceeding 100 MPa), low temperature (0 - 4 °C), high salt corrosion, and long-term maintenance-free operation. The application of deep-sea special batteries has extended from traditional military and scientific research fields to emerging directions such as energy development and environmental protection.

[0003] In the traditional technical field, the energy density of lithium-ion batteries is limited by the theoretical capacity of the positive and negative electrode materials (such as the graphite negative electrode with 372 mAh / g and the NCM622 positive electrode with 180 mAh / g), and thick electrodes easily lead to hindered ion transport. In the prior art, the silicon-based negative electrode has poor cycle life due to volume expansion problems, and the high-nickel positive electrode has capacity attenuation due to interfacial side reactions. Therefore, the present invention proposes a high energy density lithium-ion battery and a preparation method thereof to solve the problems existing in the prior art. Summary of the Invention

[0004] In view of the above problems, the object of the present invention is to provide a high energy density lithium-ion battery and a preparation method thereof. The high energy density lithium-ion battery and the preparation method thereof construct a three-dimensional conductive network through the synergy of graphene and carbon black, reduce the contact resistance, effectively improve the rate performance, and at the same time use graphene as a buffer layer between the electrolyte and the electrode, effectively reducing the interfacial impedance and inhibiting the growth of lithium dendrites. By using graphene as a buffer layer, the volume expansion of silicon is inhibited, and the problems of poor cycle life of the silicon-based negative electrode due to volume expansion and capacity attenuation of the high-nickel positive electrode due to interfacial side reactions are solved.

[0005] To achieve the object of the present invention, the present invention is realized through the following technical solutions: A high energy density lithium-ion battery and a preparation method thereof, including a high-nickel ternary positive electrode slurry, an electrode sheet, an electrolyte, and a silicon-carbon composite negative electrode slurry. The high-nickel ternary positive electrode slurry includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The silicon-carbon composite negative electrode slurry includes nano-silicon particles, graphene, and a negative electrode binder.

[0006] Further improvement lies in: The positive electrode active material is lithium nickel cobalt aluminate, the positive electrode conductive agent is a composite conductive agent mixed with graphene and carbon black, the positive electrode binder is polyvinylidene fluoride, and the negative electrode binder is sodium carboxymethyl cellulose.

[0007] A further improvement lies in that: the electrode sheet is an aluminum foil current collector, and the particle size of the nano-silicon particles is 50 - 100 nm.

[0008] It includes the following steps:

[0009] Step 1, preparing the positive electrode material: Using the mechanical liquid-phase exfoliation method, with N-methylpyrrolidone as the solvent, exfoliating flake graphite through high-speed shear grinding, obtaining few-layer graphene powder through centrifugation and freeze-drying. Then, adding graphene and carbon black into a ball mill tank in a mass ratio of 1:1 - 1:3 for ball milling and drying to obtain a conductive agent. Using lithium nickel cobalt aluminate as the active substance and polyvinylidene fluoride as the binder for mixing to obtain the positive electrode slurry;

[0010] Step 2, preparing the negative electrode material: Mixing nano-silicon particles and graphene in a mass ratio of 1:3 - 1:5, then performing ball milling and compounding, and adding sodium carboxymethyl cellulose as the binder for mixing to obtain the negative electrode slurry;

[0011] Step 3, coating and drying: Coating the positive and negative electrode slurries on the aluminum foil current collector respectively, and drying using a gradient drying process;

[0012] Step 4, rolling and slitting: Rolling the aluminum foil coated in Step 3, and slitting to form the positive electrode sheet and the negative electrode sheet;

[0013] Step 5, assembling and injecting electrolyte: Assembling the battery core using the stacking or winding process, injecting an electrolyte containing 1.2 M lithium hexafluorophosphate, and adding 2% lithium nitrate as a prelithiation additive;

[0014] Step 6, forming and encapsulating: Performing charge and discharge forming at a current of 0.1C, and using an aluminum-plastic film for soft packaging to obtain a lithium-ion battery with an energy density.

[0015] A further improvement lies in that: in Step 1, graphene and carbon black are mixed to construct a "point - surface - body" three-dimensional conductive network.

[0016] A further improvement lies in that: in Step 1, the mass ratio of the positive electrode conductive agent, lithium nickel cobalt aluminate, and polyvinylidene fluoride is 2:96:2.

[0017] A further improvement lies in that: the gradient drying process in Step 3 is divided into two stages. The first stage is pre-drying at 80°C for 3 - 5 min, and the second stage is drying at 120°C for 5 - 10 min. After drying, a positive electrode with a surface density of 400 - 600 g / m 2 and a negative electrode with a surface density of 190 - 300 g / m 2 are formed.

[0018] A further improvement lies in that: after rolling on the aluminum foil current collector in Step 4, the surface density of the positive electrode is compacted to 3.6 - 3.8 g / cm 3, the negative electrode surface density is compacted to 1.3 - 1.5 g / cm 3 .

[0019] The beneficial effects of the present invention are as follows: The present invention constructs a three-dimensional conductive network through the synergy of graphene and carbon black, reduces the contact resistance, effectively improves the rate performance. At the same time, graphene is used as a buffer layer between the electrolyte and the electrode, effectively reducing the interfacial impedance and inhibiting the growth of lithium dendrites. By using graphene as a buffer layer, the volume expansion of silicon is inhibited, solving the problems of poor cycle life caused by the volume expansion of the silicon-based negative electrode and capacity attenuation caused by interfacial side reactions of the high-nickel positive electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the process flow chart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] To deepen the understanding of the present invention, the following will further elaborate on the present invention in combination with embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0022] Embodiment 1

[0023] According to Figure 1 as shown, this embodiment provides a high-energy-density lithium-ion battery and its preparation method, including a high-nickel ternary positive electrode slurry, an electrode sheet, an electrolyte, and a silicon-carbon composite negative electrode slurry. The high-nickel ternary positive electrode slurry includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The silicon-carbon composite negative electrode slurry includes nano-silicon particles, graphene, and a negative electrode binder. The positive electrode active material is lithium nickel cobalt aluminate, the positive electrode conductive agent is a composite conductive agent mixed with graphene and carbon black, the positive electrode binder is polyvinylidene fluoride, the negative electrode binder is sodium carboxymethyl cellulose, the electrode sheet is an aluminum foil current collector, and the particle size of the nano-silicon particles is 50 nm.

[0024] It includes the following steps:

[0025] Step 1: Prepare the positive electrode material: Using the mechanical liquid-phase exfoliation method, with N-methylpyrrolidone as the solvent, exfoliate flake graphite through high-speed shear grinding, obtain few-layer graphene powder through centrifugation and freeze-drying. Then, add graphene and carbon black into the ball mill tank in a mass ratio of 1:1 for ball milling and drying, and use it as the conductive agent. Use lithium nickel cobalt aluminate as the active material, and then use polyvinylidene fluoride as the binder for mixing to obtain the positive electrode slurry. Graphene and carbon black are mixed to construct a "point-plane-body" three-dimensional conductive network. The mass ratio of the positive electrode conductive agent, lithium nickel cobalt aluminate, and polyvinylidene fluoride is 2:96:2. By constructing a three-dimensional conductive network through the synergy of graphene and carbon black, the contact resistance is reduced, and the rate performance is effectively improved. At the same time, graphene is used as a buffer layer between the electrolyte and the electrode, effectively reducing the interfacial impedance and inhibiting the growth of lithium dendrites.

[0026] Step 2: Prepare the negative electrode material: Mix nano-silicon particles and graphene at a mass ratio of 1:3, then perform ball milling and compounding. Next, add sodium carboxymethyl cellulose as a binder and mix to obtain a negative electrode slurry. By using graphene as a buffer layer, the volume expansion of silicon is effectively inhibited, improving the volume effect during the charge and discharge process of the lithium-silicon material and enhancing the battery cycle performance.

[0027] Step 3: Coating and drying: Coat the positive and negative electrode slurries on aluminum foil current collectors respectively, and use a gradient drying process for drying.

[0028] The gradient drying process is divided into two stages. In the first stage, pre-dry at 80°C for 3 minutes, and in the second stage, dry at 120°C for 5 minutes. After drying, a positive electrode with a surface density of 400 - 600 g / m 2 and a negative electrode with a surface density of 190 - 300 g / m 2 are formed. By gradually increasing the temperature, the solvent evaporation rate is slowed down, promoting the uniform distribution of the active material and the conductive agent, enhancing the electrode conductivity. Through segmented drying, coating cracking or "skin" effect is reduced, and the microporous channels required for electrolyte infiltration are retained, thereby improving the battery rate performance.

[0029] Step 4: Rolling and slitting: Roll the aluminum foil coated in Step 3, and after slitting, form positive electrode sheets and negative electrode sheets.

[0030] After rolling on the aluminum foil current collector, the surface density of the positive electrode is compacted to 3.6 - 3.8 g / cm 3 and the surface density of the negative electrode is compacted to 1.3 - 1.5 g / cm 3 . By increasing the electrode surface density and compaction density, the proportion of non-active materials is effectively reduced.

[0031] Step 5: Assembly and injection: Assemble the battery cells using the stacking or winding process, inject an electrolyte containing 1.2% lithium hexafluorophosphate, and add 2% lithium nitrate as a prelithiation additive.

[0032] Step 6: Formation and encapsulation: Perform charge and discharge formation at a current of 0.1C, and use an aluminum-plastic film for soft packaging to obtain a lithium-ion battery with a high energy density.

[0033] Example 2

[0034] According to Figure 1As shown in the figure, this embodiment provides a high-energy-density lithium-ion battery and its preparation method, including a high-nickel ternary positive electrode slurry, an electrode sheet, an electrolyte, and a silicon-carbon composite negative electrode slurry. The high-nickel ternary positive electrode slurry includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The silicon-carbon composite negative electrode slurry includes nano-silicon particles, graphene, and a negative electrode binder. The positive electrode active material is lithium nickel cobalt aluminate, the positive electrode conductive agent is a composite conductive agent mixed with graphene and carbon black, the positive electrode binder is polyvinylidene fluoride, the negative electrode binder is sodium carboxymethyl cellulose, the electrode sheet is an aluminum foil current collector, and the particle size of the nano-silicon particles is 70 nm.

[0035] It includes the following steps:

[0036] Step 1, prepare the positive electrode material: Using the mechanical liquid-phase exfoliation method, with N-methylpyrrolidone as the solvent, exfoliate flake graphite by high-speed shear grinding, and obtain few-layer graphene powder through centrifugation and freeze-drying. Then, add graphene and carbon black into the ball mill tank at a mass ratio of 1:2 for ball milling and drying, and use it as the conductive agent. Use lithium nickel cobalt aluminate as the active material, and then use polyvinylidene fluoride as the binder for mixing to obtain the positive electrode slurry. The graphene and carbon black are mixed to construct a "point-plane-body" three-dimensional conductive network. The mass ratio of the positive electrode conductive agent, lithium nickel cobalt aluminate, and polyvinylidene fluoride is 2:96:2. By synergistically constructing a three-dimensional conductive network with graphene and carbon black, the contact resistance is reduced, the rate performance is effectively improved. At the same time, using graphene as a buffer layer between the electrolyte and the electrode effectively reduces the interfacial impedance and inhibits the growth of lithium dendrites.

[0037] Step 2, prepare the negative electrode material: Mix nano-silicon particles and graphene at a mass ratio of 1:4 and then perform ball milling and compounding, and then add sodium carboxymethyl cellulose as the binder for mixing to obtain the negative electrode slurry. By using graphene as a buffer layer, the volume expansion of silicon is effectively inhibited, the improvement of the volume effect during the charge and discharge process of the lithium-silicon material is realized, and the cycle performance of the battery is enhanced;

[0038] Step 3, coating and drying: Coat the positive and negative electrode slurries on the aluminum foil current collector respectively, and use a gradient drying process for drying;

[0039] The gradient drying process is divided into two stages. The first stage is pre-drying at 80 °C for 4 min, and the second stage is drying at 120 °C for 7 min. After drying, a positive electrode with a surface density of 400 - 600 g / m 2 and a negative electrode with a surface density of 190 - 300 g / m 2 are formed. By gradually increasing the temperature, the solvent evaporation rate is slowed down, the uniform distribution of the active material and the conductive agent is promoted, the electrode conductivity is improved, and the coating cracking or "skin" effect is reduced through segmented drying, and the microporous channels required for electrolyte infiltration are retained, thereby improving the battery rate performance.

[0040] Step 4: Roll pressing and slitting: The aluminum foil coated in Step 3 is roll pressed and slit to form a positive electrode sheet and a negative electrode sheet;

[0041] After roll pressing on the aluminum foil current collector, the positive electrode surface density is compacted to 3.6 - 3.8 g / cm 3 , and the negative electrode surface density is compacted to 1.3 - 1.5 g / cm 3 , effectively reducing the proportion of inactive materials by increasing the electrode surface density and compaction density.

[0042] Step 5: Assembly and electrolyte injection: The battery cells are assembled using the stacking or winding process, and an electrolyte containing 1.2% lithium hexafluorophosphate is injected, and 2% lithium nitrate is added as a prelithiation additive;

[0043] Step 6: Formation and encapsulation: Charge and discharge formation is carried out at a current of 0.1C, and soft packaging with an aluminum-plastic film is used to obtain a lithium-ion battery with a high energy density.

[0044] Example 3

[0045] According to Figure 1 as shown, this example provides a high energy density lithium-ion battery and its preparation method, including a high-nickel ternary positive electrode paste, an electrode sheet, an electrolyte, and a silicon-carbon composite negative electrode paste. The high-nickel ternary positive electrode paste includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The silicon-carbon composite negative electrode paste includes nano-silicon particles, graphene, and a negative electrode binder. The positive electrode active material is lithium nickel cobalt aluminate, the positive electrode conductive agent is a composite conductive agent of graphene and carbon black, the positive electrode binder is polyvinylidene fluoride, the negative electrode binder is sodium carboxymethylcellulose, the electrode sheet is an aluminum foil current collector, and the particle size of the nano-silicon particles is 100 nm.

[0046] It includes the following steps:

[0047] Step 1: Preparation of the positive electrode material: Using the mechanical liquid-phase exfoliation method, with N-methylpyrrolidone as the solvent, flake graphite is exfoliated by high-speed shear grinding, and few-layer graphene powder is obtained through centrifugation and freeze-drying. Then, graphene and carbon black are added to the ball mill tank in a mass ratio of 1:3 for ball milling and drying to be used as the conductive agent. Using lithium nickel cobalt aluminate as the active material and polyvinylidene fluoride as the binder for mixing to obtain the positive electrode paste. Graphene and carbon black are mixed to construct a "point-plane-body" three-dimensional conductive network. The mass ratio of the positive electrode conductive agent, lithium nickel cobalt aluminate, and polyvinylidene fluoride is 2:96:2. By synergistically constructing a three-dimensional conductive network with graphene and carbon black, the contact resistance is reduced, and the rate performance is effectively improved. At the same time, using graphene as a buffer layer between the electrolyte and the electrode effectively reduces the interfacial impedance and inhibits the growth of lithium dendrites.

[0048] Step 2: Prepare the negative electrode material: Mix nano-silicon particles and graphene in a mass ratio of 1:5, then perform ball milling and compounding. Next, add sodium carboxymethyl cellulose as a binder and mix to obtain a negative electrode slurry. By using graphene as a buffer layer, the volume expansion of silicon is effectively inhibited, improving the volume effect during the charge and discharge process of the lithium-silicon material and enhancing the battery cycle performance.

[0049] Step 3: Coating and drying: Coat the positive and negative electrode slurries on aluminum foil current collectors respectively, and use a gradient drying process for drying.

[0050] The gradient drying process is divided into two stages. In the first stage, pre-dry at 80°C for 5 minutes, and in the second stage, dry at 120°C for 10 minutes. After drying, a positive electrode with a surface density of 400 - 600 g / m 2 and a negative electrode with a surface density of 190 - 300 g / m 2 are formed. By gradually increasing the temperature, the solvent evaporation rate is slowed down, promoting the uniform distribution of active materials and conductive agents, enhancing the electrode conductivity. Through segmented drying, coating cracking or "skin" effects are reduced, and the microporous channels required for electrolyte infiltration are retained, thereby improving the battery rate performance.

[0051] Step 4: Rolling and slitting: Roll the aluminum foil coated in Step 3, and after slitting, form positive electrode sheets and negative electrode sheets.

[0052] After rolling on the aluminum foil current collector, the surface density of the positive electrode is compacted to 3.6 - 3.8 g / cm 3 and the surface density of the negative electrode is compacted to 1.3 - 1.5 g / cm 3 . By increasing the electrode surface density and compaction density, the proportion of inactive materials is effectively reduced.

[0053] Step 5: Assembly and electrolyte injection: Assemble the battery cells using the stacking or winding process, inject an electrolyte containing 1.2% lithium hexafluorophosphate, and add 2% lithium nitrate as a prelithiation additive.

[0054] Step 6: Formation and encapsulation: Perform charge and discharge formation at a current of 0.1C, and use an aluminum-plastic film for soft packaging to obtain a lithium-ion battery with a high energy density.

[0055] The lithium-ion batteries prepared in Example 1, Example 2, and Example 3 were subjected to charge and discharge cycling at room temperature, and a commercially available traditional lithium-ion battery (Panasonic NCR18650B 18650 3400 mAh 3.6V lithium-ion rechargeable battery) was used as a comparison. The current density was 1 A / g -1, with a voltage range of 0.5 to 3.5 V, cycle 200 times, record the initial capacity of the sodium-ion battery and the capacity after 200 cycles, and calculate the average capacity attenuation rate per cycle. The average capacity attenuation rate per cycle = (initial capacity - capacity after 200 cycles) / initial capacity / 200. The test results are shown in Table 1 below:

[0056] Table 1 Test Results Table

[0057] Average capacity decay rate per turn Specific capacity Example 1 0.13％ 366 Example 2 0.15％ 350 Example 3 0.12％ 332 Comparative example 0.36％ 325

[0058] As can be seen from Table 1 above, compared with traditional lithium-ion batteries, the sodium-ion batteries prepared in Example 1, Example 2, and Example 3 of the present invention have a lower capacity attenuation rate, that is, a higher cycle life.

[0059] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A high energy density lithium-ion battery, characterized in that: It includes a high-nickel ternary cathode slurry, an electrode sheet, an electrolyte, and a silicon-carbon composite anode slurry. The high-nickel ternary cathode slurry includes a cathode active material, a cathode conductive agent, and a cathode binder. The silicon-carbon composite anode slurry includes nano-silicon particles, graphene, and an anode binder.

2. The high-energy density lithium-ion battery according to claim 1, characterized in that: The cathode active material is lithium nickel cobalt aluminate, the cathode conductive agent is a composite conductive agent mixed with graphene and carbon black, the cathode binder is polyvinylidene fluoride, and the anode binder is sodium carboxymethyl cellulose.

3. A high energy density lithium ion battery and a preparation method thereof according to claim 1, characterized in that: The electrode sheet is an aluminum foil current collector, and the particle size of the nano-silicon particles is 50-100 nm.

4. A preparation method of a high-energy density lithium-ion battery, comprising the following steps: Step 1, preparing a cathode material: Using the mechanical liquid-phase exfoliation method, with N-methylpyrrolidone as a solvent, exfoliating flake graphite by high-speed shear grinding, obtaining few-layer graphene powder through centrifugation and freeze-drying, and then adding graphene and carbon black into a ball mill tank in a mass ratio of 1:1-1:3 for ball milling and drying to be used as a conductive agent, using lithium nickel cobalt aluminate as the active material, and then using polyvinylidene fluoride as a binder for mixing to obtain a cathode slurry; Step 2, preparing an anode material: Mixing nano-silicon particles and graphene in a mass ratio of 1:3-1:5 and then performing ball milling and compounding, and then adding sodium carboxymethyl cellulose as a binder for mixing to obtain an anode slurry; Step 3, coating and drying: Coating the positive and negative slurries on the aluminum foil current collector respectively, and drying using a gradient drying process; Step 4, rolling and slitting: Rolling the aluminum foil coated in Step 3, and slitting to form a positive electrode sheet and a negative electrode sheet; Step 5, assembling and injecting electrolyte: Assembling the battery core using the stacking or winding process, injecting an electrolyte containing 1.2 M lithium hexafluorophosphate, and adding 2% lithium nitrate as a prelithiation additive; Step 6, forming and encapsulating: Performing charge and discharge forming at a current of 0.1 C, and using an aluminum-plastic film for soft packaging to obtain a lithium-ion battery with an energy density.

5. A method for a high energy density lithium-ion battery according to claim 4, characterized in that: In Step 1, graphene and carbon black are mixed to construct a "point-plane-body" three-dimensional conductive network.

6. A method for a high energy density lithium ion battery according to claim 4, characterized in that: In Step 1, the mass ratio of the cathode conductive agent, lithium nickel cobalt aluminate, and polyvinylidene fluoride is 2:96:

2.

7. A method for a high energy density lithium ion battery according to claim 4, characterized in that: The gradient drying process in the third step is divided into two stages. In the first stage, pre-drying is carried out at 80 °C for 3 - 5 minutes, and in the second stage, drying is carried out at 120 °C for 5 - 10 minutes. After drying is completed, a positive electrode with a surface density of 400 - 600 g / m 2 and a negative electrode with a surface density of 190 - 300 g / m 2 are formed.

8. A method for a high energy density lithium ion battery according to claim 4, characterized in that: In the fourth step, after rolling, the positive electrode surface density on the aluminum foil current collector is compacted to 3.6 - 3.8 g / cm 3 , and the negative electrode surface density is compacted to 1.3 - 1.5 g / cm 3 .

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