Preparation method of high-performance modified dry electrode and application of high-performance modified dry electrode in lithium metal battery

Abstract

The invention discloses a preparation method of a high-performance modified dry-method electrode and application of the high-performance modified dry-method electrode in a lithium metal battery, the method comprises the following steps: step 1, heating and hot-melting succinonitrile under a hydrothermal condition to obtain clear and transparent liquid, and then adding lithium salt into the clear and transparent liquid to complete preparation of a dry-method modified additive; 2, premixing a positive electrode material, vapor-phase growth carbon fibers and a dry-method modified additive; 3, adding an adhesive into the premixed material to obtain a modified dry-method electrode material; and step 4, pouring the modified dry-method electrode powder into a mortar, after preliminary film formation, gradually thinning to 60-75 m in thickness under a roller press, and finally performing hot rolling with a current collector to complete the preparation of the modified dry-method electrode. According to the invention, by adding the additive into the dry electrode, an excellent high-voltage-resistant electrode interface is constructed, and the lithium ion conduction rate of the electrode is improved, so that the electrochemical performance of the dry electrode is further improved, and the application of the dry electrode in a high-voltage lithium metal battery is promoted.

Description

Technical Field

[0001] This invention belongs to the field of energy storage materials and relates to a method for preparing a dry electrode. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage devices to meet the various needs of social production. However, the problems of traditional wet electrode preparation cannot be solved by existing processes: (1) The produced battery requires about 42 kWh of energy to evaporate the organic solvent NMP used in the wet process; in addition, due to the reproductive toxicity of NMP, large and complex industrial equipment is required to safely remove NMP. This process consumes a huge amount of energy, and the cost accounts for about 3% of the overall battery pack cost. (2) Electrode delamination: During the solvent evaporation process, binders and conductive agents diffuse to the vicinity of the electrode surface and form agglomerates, while active materials precipitate, which leads to a decrease in the overall integrity of the electrode and damages the electrode integrity, causing the electrode to dry and crack and shed powder. (3) Limited electrode thickness: High-capacity electrodes manufactured by wet coating technology have problems such as cracks, delamination, and poor flexibility, which seriously restricts the process of preparing high-energy-density batteries and cannot meet the needs of energy storage development. (4) Poor matching degree with solid electrolyte: The electrode surface prepared by traditional wet process has solvent residue, which produces serious side reactions with solid electrolyte, restricting the development of solid-state batteries.

[0003] In contrast, the dry process does not utilize NMP solvents to prepare the slurry and eliminates the need for solvent evaporation drying, offering significant advantages in terms of carbon emissions and processing costs. Furthermore, the high-capacity electrodes manufactured using dry electrode technology maintain uniform composition throughout the electrode. However, the thicker electrode significantly hinders the insertion and extraction of lithium ions during charging and discharging; additionally, the high electronic insulation of the binder, polytetrafluoroethylene (PTFE), results in a higher interfacial impedance for dry electrodes. Therefore, the construction of efficient lithium-ion transport channels is still necessary. Summary of the Invention

[0004] To address the shortcomings of dry-process technology and commercial electrolytes, this invention provides a method for preparing a high-performance modified dry-process electrode and its application in lithium metal batteries. By adding additives to the dry-process electrode, this invention constructs an excellent high-voltage resistant electrode interface, improves the lithium-ion conduction rate of the electrode, and thus further enhances the electrochemical performance of the dry-process electrode, thereby promoting its application in high-voltage lithium metal batteries.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for preparing a high-performance modified dry electrode includes the following steps:

[0007] Step 1: Under hydrothermal conditions, heat succinate to melt it into a clear and transparent liquid. Then, add lithium salt to it, controlling the mass ratio of succinate to lithium salt to be 10:0.5~2. Stir until completely dissolved to complete the preparation of the dry-process modified additive. The lithium salt should be soluble in the selected succinate and not react with it. It is one of lithium nonafluorobutyl sulfonate, lithium nitrate, lithium bis(oxalato)borate, or lithium tetrafluoroborate. The heating temperature is 60~90℃, and the heating equipment is one of a water bath and a heating stirrer.

[0008] Step 2: Premix the cathode material, vapor-grown carbon fiber, and dry modification additives, wherein the cathode material is one of lithium nickel manganese oxide, nickel cobalt manganese ternary material, and lithium cobalt oxide.

[0009] Step 3: Add a binder to the premixed material obtained in Step 2 to obtain a modified dry electrode material, wherein the mass ratio of positive electrode material, vapor-grown carbon fiber, binder, and dry modification additive is 0.8~0.9:0.1~0.05:0.03~0.015:0.07~0.035, and the binder is polytetrafluoroethylene;

[0010] Step 4: Pour the modified dry electrode powder obtained in Step 3 into a mortar and grind for 10-30 min. After preliminary film formation, gradually reduce the thickness to 60-75 µm under a roller press. Finally, hot roll press with the current collector to complete the preparation of the modified dry electrode. The current collector is carbon-coated aluminum foil, and the hot roll pressing temperature is 100-120℃.

[0011] An application of the modified dry electrode prepared by the above method in a lithium metal battery, wherein the lithium metal battery uses the modified dry electrode as the positive electrode, lithium metal as the negative electrode, and 1.5% LiDFOB is added to the electrolyte.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] 1. This invention proposes a dry-process modification additive for long-term cycling operation of high-voltage dry-process cathode / lithium metal anode batteries. This dry-process modification additive utilizes the thermoplasticity of succinic anionylene to dissolve lithium nonafluorobutyl sulfonate, forming a clear and transparent modified additive. The thermoplasticity of succinic anionylene and the presence of nitrile functional groups effectively enhance the flexibility of the dry-process electrode film and construct efficient lithium-ion transport channels, thereby improving lithium-ion transport efficiency and reducing the negative impact of thick electrodes on conductivity. Simultaneously, the electronegativity of the sulfonic acid functional groups in lithium nonafluorobutyl sulfonate anchors transition metals nickel and manganese to the cathode surface, inhibiting transition metal solvation and protecting the integrity of lithium nickel manganese oxide crystals during electrode cycling. The dry-process modification additive, composed of these two components, significantly improves the cycle life of lithium batteries.

[0014] 2. This invention utilizes polytetrafluoroethylene (PTFE) binder to prepare high-load spinel-type lithium nickel manganese oxide (LNMO) electrodes via a dry process. This reduces electrode manufacturing costs, eliminates the need for drying, significantly shortens preparation time, and improves production efficiency. Furthermore, its charging voltage is higher than that of ternary electrode materials, reaching 4.85V. The LNMO electrode is cobalt-free, further reducing production costs while significantly improving battery energy density despite its high load. The addition of succinic anionyl nitrile and lithium nonafluorobutyl sulfonate (SN-LNBS) modifiers resolves the interfacial incompatibility and low flexibility inherent in dry-process electrodes. Simultaneously, the formed positive electrode protective layer inhibits the decomposition of commercial electrolytes under high voltage, and the introduction of nitrile and sulfonic acid groups enhances lithium-ion migration efficiency.

[0015] 3. To further improve battery energy density, this invention uses a lithium metal anode instead of a traditional graphite electrode. The high specific capacity of lithium metal (3860 mAh / g) is better suited to a high-load cathode. Furthermore, the addition of succinic anion and lithium nonafluorobutyl sulfonate to the cathode material optimizes the lithium-ion transport pathway. The preferential decomposition and film formation of lithium difluorooxalate borate (LiODFB) on the anode side of the electrolyte suppresses lithium dendrite formation on the lithium metal anode due to uneven lithium-ion transport and diffusion, thus preventing SEI film rupture caused by excessive expansion coefficient of the lithium metal anode during battery charging and discharging, and reducing excessive lithium-ion loss. Attached Figure Description

[0016] Figure 1 The images show the XRD patterns of the modified and unmodified dry electrodes obtained in Example 1 before and after cycling.

[0017] Figure 2 The graph shows the C / 3 long cycle test curves of different electrode processes obtained in Example 1;

[0018] Figure 3 The AC impedance spectra of the modified and unmodified dry electrodes obtained in Example 1 are shown.

[0019] Figure 4 The stress-strain diagrams for the modified and unmodified dry electrodes obtained in Example 1 are shown.

[0020] Figure 5 The graph shows the charge-discharge lithium-ion transport rates of the modified and unmodified dry electrodes obtained in Example 1.

[0021] Figure 6 The images show the actual dry and wet electrodes obtained in Example 1. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0023] This invention provides a method for preparing a high-performance modified dry electrode, the method comprising the following steps:

[0024] Step 1: Under hydrothermal conditions, heat succinate to melt it into a clear and transparent liquid. Then, add lithium salt to it, controlling the mass ratio of succinate to lithium salt to be 10:0.5~2. Stir until completely dissolved to complete the preparation of the dry-process modified additive. The lithium salt should be soluble in the selected succinate and not react with it. It is one of lithium nonafluorobutyl sulfonate, lithium nitrate, lithium bis(oxalato)borate, or lithium tetrafluoroborate. The heating temperature is 60~90℃, and the heating equipment is one of a water bath and a heating stirrer.

[0025] Step 2: Premix the cathode material, vapor-grown carbon fiber, and dry modification additive in a ball mill. Program settings: rotation speed 180~200 r / min, ball milling 100~120 min. The cathode material is one of lithium nickel manganese oxide, nickel cobalt manganese ternary material, and lithium cobalt oxide. The ball milling method can be replaced by the grinding method.

[0026] Step 3: Add a binder to the premixed material obtained in Step 2. Set the program to: 180~200 r / min rotation speed, ball mill for 330~450 min to obtain the modified dry electrode material. The mass ratio of the positive electrode material, vapor-grown carbon fiber, binder, and dry modification additive is 0.8~0.9:0.1~0.05:0.03~0.015:0.07~0.035. The binder is polytetrafluoroethylene.

[0027] Step 4: Pour the modified dry electrode powder obtained in Step 3 into a mortar and grind for 10-30 min. After preliminary film formation, gradually reduce the thickness to 60-75 µm under a roller press. Finally, hot roll press with the current collector to complete the preparation of the modified dry electrode. The current collector is carbon-coated aluminum foil, and the hot roll pressing temperature is 100-120℃.

[0028] Example 1:

[0029] 0.6363g of succinic anionylene was completely melted into a clear, transparent liquid in a 60℃ water bath. Then, 0.0636g of lithium nonafluorobutyl sulfonate was added to the liquid and stirred until completely dissolved. This solution was then added to a mixture of 8g of lithium nickel manganese oxide and 1g of vapor-grown carbon fiber powder. This mixture was pre-mixed in a ball mill at 180 rpm for 100 min. Subsequently, 0.3g of polytetrafluoroethylene (PTFE) was added to the pre-mixed powder, and the mixture was ball-milled at 200 rpm for 330 min to complete the mixing of the dry electrode material. The mixed dry electrode powder was poured into a mortar and ground for 15 min to form a preliminary film. This film was then gradually thinned to 75µm using a roller press. Finally, it was laminated with carbon-coated aluminum foil at 100℃ to prepare the modified dry electrode.

[0030] The modified dry electrode obtained in this embodiment can be used as the positive electrode in the assembly of coin cell lithium metal batteries. The coin cell lithium metal battery uses lithium metal as the negative electrode, EC and EMC as solvents, LiPF6 as electrolyte, and LiDFOB is added. The volume ratio of EC to EMC is 3:7, the concentration of LiPF6 is 1.0 mol / L, and the amount of LiDFOB added is 1.5%.

[0031] Depend on Figure 1 X-ray diffraction tests showed that dry-process electrodes containing modified additives can effectively suppress lattice distortion and collapse of lithium nickel manganese oxide cathode materials during cycling, thereby maintaining the structural stability of the cathode material. Figure 2 The cyclic test curves show that at a current density of C / 3 and 16.8 mg / cm³, 2 Under high load conditions, the capacity retention rate of the dry-process battery using modified additives after 215 cycles is 85.02%, which is much higher than that of ordinary dry-process and traditional wet-process batteries. Figure 3 The figure shows the EIS impedance test of the dry electrode. The projection of the semicircle on the X-axis represents the interface impedance of the electrode. It can be clearly seen that the addition of SN-LNBS greatly reduces the interface impedance of the dry electrode. Figure 4 The stress-strain diagrams of modified and unmodified dry electrodes clearly show that the addition of additives significantly improves the vertical uniformity of the dry electrodes and promotes robust mechanical properties. Through... Figure 5 A comparison of the ion diffusion coefficients of the modified and unmodified dry electrodes shows that, under most potential conditions, the modified electrode exhibits a faster ion diffusion rate than the unmodified electrode. The addition of modifiers can effectively enhance the diffusion kinetics of ions within the electrode, thereby increasing the charge / discharge specific capacity of the electrode. Figure 6As shown in (a), the flexibility of the modified dry electrode is greatly improved. After roll drying, no cracks appear on the electrode surface, and no cracks appear on the electrode film surface even after repeated folding, demonstrating the superiority of the dry electrode in preparing high-load electrodes; while as Figure 6 As shown in (b), after drying, the wet electrode under the same load exhibited a large amount of powder shedding, with the electrode material falling off the current collector and the electrode integrity being poor.

[0032] Example 2:

[0033] The difference between this embodiment and Embodiment 1 is that the lithium salt is lithium nitrate.

[0034] Example 3:

[0035] The difference between this embodiment and Embodiment 1 is that the lithium salt is lithium bis(oxalatoborate).

[0036] Example 4:

[0037] The difference between this embodiment and Embodiment 1 is that the lithium salt is lithium tetrafluoroborate.

[0038] Example 5:

[0039] The difference between this embodiment and Embodiment 1 is that the positive electrode material is a nickel-cobalt-manganese ternary electrode material.

[0040] Example 6:

[0041] The difference between this embodiment and Embodiment 1 is that the positive electrode material is lithium cobalt oxide electrode material.

[0042] Example 7:

[0043] The difference between this embodiment and Example 1 is that the mass ratio of the modifier succinic anion and lithium salt is 10:2.

[0044] Example 8:

[0045] The difference between this embodiment and Embodiment 1 is that the mass ratio of the cathode material, vapor-grown carbon fiber, polytetrafluoroethylene, and modifying additives is 0.9 : 0.05 : 0.015 : 0.035.

Claims

1. A method for preparing a high-performance modified dry electrode, characterized in that... The method includes the following steps: Step 1: Under hydrothermal conditions, succinate is heated to melt into a clear and transparent liquid. Then, lithium salt is added to it, and the mass ratio of succinate to lithium salt is controlled at 10:0.5~2. Stir until completely dissolved to complete the preparation of dry modified additive. Step 2: Premix the cathode material, vapor-grown carbon fiber, and dry modification additives; Step 3: Add a binder to the premixed material obtained in Step 2 to obtain a modified dry electrode material, wherein the mass ratio of positive electrode material, vapor-grown carbon fiber, binder, and dry modification additive is 0.8~0.9:0.1~0.05:0.03~0.015:0.07~0.035; Step 4: Pour the modified dry electrode powder obtained in Step 3 into a mortar, and after preliminary film formation, gradually thin it to a thickness of 60~75 µm under a roller press. Finally, hot roller press it with the current collector to complete the preparation of the modified dry electrode.

2. The method for preparing the high-performance modified dry electrode according to claim 1, characterized in that... In step 1, the lithium salt is one of lithium nonafluorobutyl sulfonate, lithium nitrate, lithium bis(oxalato)borate, or lithium tetrafluoroborate.

3. The method for preparing the high-performance modified dry electrode according to claim 1, characterized in that... In step 1, the heating temperature is 60~90℃, and the heating equipment is either a water bath or a heating stirrer.

4. The method for preparing the high-performance modified dry electrode according to claim 1, characterized in that... In step 2, the cathode material is one of lithium nickel manganese oxide, nickel cobalt manganese ternary material, and lithium cobalt oxide.

5. The method for preparing the high-performance modified dry electrode according to claim 1, characterized in that... In step 3, the adhesive is polytetrafluoroethylene.

6. The method for preparing the high-performance modified dry electrode according to claim 1, characterized in that... In step 4, the grinding time is 10~30 min.

7. The method for preparing the high-performance modified dry electrode according to claim 1, characterized in that... In step 4, the current collector is a carbon-coated aluminum foil.

8. The method for preparing the high-performance modified dry electrode according to claim 1, characterized in that... In step 4, the hot rolling temperature is 100~120℃.

9. The application of a modified dry electrode prepared by any one of claims 1-8 in a lithium metal battery.

10. The application of the modified dry electrode according to claim 9 in lithium metal batteries, characterized in that... The lithium metal battery uses a modified dry electrode as the positive electrode and lithium metal as the negative electrode, with 1.5% LiDFOB added to the electrolyte.

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