High specific energy lithium battery aqueous positive electrode slurry, preparation method and application thereof

Abstract

The application provides a high specific energy lithium battery aqueous positive electrode slurry, a preparation method and application thereof. The slurry comprises a positive electrode active material, a conductive agent, a binder and a mixed solvent in a mass ratio of (85-95):(1-8):(1-8):(200-400). The binder comprises a first binder xanthan gum and a second binder in a mass ratio of 50-100:0-50. The second binder is selected from one or more of polyethylene oxide, polyethylene glycol, sodium alginate and sodium carboxymethyl cellulose. The mixed solvent is a mixture of water and a polar organic solvent. The polar organic solvent is selected from one or more of ethanol, n-propanol and acetone. The molecular chain of xanthan gum can be elongated in the mixed solvent, and the morphology of xanthan gum can be changed. Xanthan gum can better coat and connect the positive electrode active material and the conductive agent. The binder is stable to electrolyte and does not swell, which can effectively reduce the side reaction between the electrolyte and the positive electrode active material, thereby improving the initial coulomb efficiency of the battery and the cycle life of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and particularly relates to a high-energy-density aqueous positive electrode slurry for lithium batteries, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are widely used in mobile devices, laptops, and mobile communications due to their advantages such as no memory effect, high safety, and high specific energy. They are also well-suited for use in hybrid and electric vehicles. The performance and cost of lithium-ion batteries depend on the cathode material. Commercially available lithium-ion battery cathode materials mainly include lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), and ternary materials (NMC). To further improve battery life or the driving range of electric vehicles, choosing lithium-rich manganese-based layered oxide cathode materials (≥250mAh / g) with higher specific capacity is a good option. However, their current application in batteries faces problems such as poor cycle performance and insufficient safety, which seriously restricts their rapid development and application.

[0003] Binders are crucial components of the positive and negative electrodes in lithium-ion batteries. Their main function is to bind active materials, conductive agents, and current collectors, stabilize the electrode structure, buffer volume changes during charge and discharge, maintain electrode structural integrity, and ensure the electrode materials can repeatedly insert and extract lithium. Binder failure leads to the loss of conductive connections between different electrode components, and some active material particles become insulated, unable to participate in charge and discharge, resulting in a decline in battery electrochemical performance. Therefore, selecting a suitable binder is essential.

[0004] Currently, in the industrial production of lithium batteries, the binder used in the positive electrode sheet is mainly polyvinylidene fluoride (PVDF), and the dispersant is the polar organic solvent N-methylpyrrolidone (NMP). This binder has good stability in the electrolyte and also has good adhesion. However, PVDF also has its own drawbacks, such as reacting with metallic lithium and Lithium at higher temperatures. x C6 undergoes an exothermic reaction, posing significant safety hazards. Furthermore, PVDF has poor electronic and ionic conductivity, leading to swelling in the electrolyte and altering the electrode structure, thus affecting battery performance. Additionally, PVDF readily absorbs water, resulting in weakened adhesion; therefore, strict control of moisture levels in the storage environment is necessary, increasing production costs. Moreover, PVDF requires large amounts of NMP, which is highly volatile, toxic, flammable, and explosive, severely polluting the environment and endangering the health of production workers. Therefore, seeking novel green binders to replace polar organic solvent-based PVDF is of significant and far-reaching importance, meeting the development trend of green industry. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a high-energy-density aqueous cathode slurry for lithium batteries, its preparation method and application, which can improve the first coulombic efficiency of lithium batteries.

[0006] This invention provides a high-energy-density aqueous positive electrode slurry for lithium batteries, comprising a positive electrode active material, a conductive agent, a binder, and a mixed solvent in a mass ratio of (85-95):)(1-8):(1-8):(200-400).

[0007] The adhesive comprises a first adhesive and a second adhesive in a mass ratio of 50-100:0-50; the mass ratio of the first adhesive and the second adhesive is preferably 70-100:0-30, more preferably 80-95:5-20;

[0008] The first adhesive is xanthan gum;

[0009] The second adhesive is selected from one or more of polyethylene oxide, polyethylene glycol, sodium alginate, and sodium carboxymethyl cellulose;

[0010] The mixed solvent is a mixture of water and a polar organic solvent; the polar organic solvent is selected from one or more of ethanol, n-propanol, and acetone. This invention uses water as the main solvent for the slurry. Water can dissolve xanthan gum, while the polar organic solvent is insoluble in xanthan gum but miscible with water. Together, they act as dispersants for the slurry. This mixed solvent is more conducive to the dispersion of the positive electrode active material and the conductive agent in the aqueous slurry.

[0011] In this invention, the first adhesive is insoluble in the polar organic solvent.

[0012] In this invention, the preferred mass ratio of the positive electrode active material, conductive agent, binder and mixed solvent is (90-95):)(2-5):(2-5):(300-350).

[0013] In this invention, the polar organic solvent accounts for 10-60% of the mass of water, preferably 25-35%.

[0014] In this invention, the relative molecular weight of the second adhesive is 1×10⁻⁶. 4 ~2×10 6 ;

[0015] The relative molecular weight of the xanthan gum is 1×10⁻⁶. 5 ~2×10 8 .

[0016] In this invention, the positive electrode active material is selected from lithium-rich manganese-based substrate oxides having the composition of Formula I:

[0017] x Li2MnO3.(1-x)LiMO2 Formula I;

[0018] M is a transition metal, such as Ni, Co, or Mn, and 0.1 <x<0.7。

[0019] The aforementioned lithium-rich manganese-based morphological oxide was produced by Ningbo Fuli Battery Materials Technology Co., Ltd.

[0020] In this invention, the conductive agent is selected from one or more of acetylene black, Super P, graphene, carbon nanotubes and Ketjen black.

[0021] This invention provides a method for preparing the high-energy-density lithium battery aqueous cathode slurry described in the above-mentioned technical solution, comprising the following steps:

[0022] The first and second binders are dissolved in a mixed solvent, and then a conductive agent and positive electrode active material are added and mixed to obtain a high-energy-density lithium battery aqueous positive electrode slurry.

[0023] This invention provides a high-energy-density aqueous positive electrode sheet for lithium batteries, which is prepared by coating the aqueous positive electrode slurry described in the above technical solution onto a current collector and then drying it.

[0024] In this invention, the coating thickness is 100–2000 micrometers. This invention can coat the aqueous positive electrode slurry on one side or both sides of the current collector. The dried electrode sheet is cut into the shape required for the corresponding lithium-ion battery model and stored for later use. The areal density of the positive electrode active material in the coated positive electrode slurry is greater than 20 mg / cm³. 2 The unit coating area capacity is greater than 5 mAh / cm². 2 .

[0025] This invention provides a lithium battery, comprising the high-energy-density lithium battery aqueous positive electrode, negative electrode, separator, and electrolyte described in the above technical solution.

[0026] The positive electrode plate improves the side reactions of the electrolyte and the positive electrode, increases the cycle life of the battery, reduces the manufacturing cost of the battery, and is also more environmentally friendly.

[0027] In this invention, the negative electrode is selected from graphite, silicon, or lithium foil;

[0028] The lithium battery type is selected from button cells, pouch cells, 18650 cells, or square aluminum-cased cells.

[0029] This invention provides a high-energy-density lithium battery aqueous positive electrode slurry, comprising a positive electrode active material, a conductive agent, a binder, and a mixed solvent in a mass ratio of (85-95):)(1-8):(1-8):(200-400); the binder comprises a first binder and a second binder in a mass ratio of 50-100:0-50; the first binder is xanthan gum; the second binder is selected from one or more of polyethylene oxide, polyethylene glycol, sodium alginate, and sodium carboxymethyl cellulose; the mixed solvent is a mixture of water and a polar organic solvent; the polar organic solvent is selected from one or more of ethanol, n-propanol, and acetone. The aqueous positive electrode slurry provided by this invention uses an aqueous dispersion system with a mixture of water and polar organic solvent as a binder. In the above mixed solvent, the molecular chain of the binder xanthan gum can be elongated and its morphology can be varied, which can better encapsulate and connect the positive electrode active material and the conductive agent. The above binder is stable to the electrolyte and does not swell, which can effectively reduce the side reactions between the electrolyte and the positive electrode active material, thereby improving the first coulombic efficiency of the battery and increasing the cycle life of the battery. Attached Figure Description

[0030] Figure 1 The first charge-discharge capacity-voltage curves (0.1C, 2.0-4.6V) of batteries using the positive electrode slurry prepared in Examples 1, 3 and 4 of this invention.

[0031] Figure 2 The first charge-discharge curves (0.1C, 2.0-4.8V) of the batteries using the positive electrode slurry prepared in Example 1 and Comparative Example 5 of this invention.

[0032] Figure 3 The first charge-discharge curves (0.1C, 2.0-4.8V) of the batteries using the positive electrode slurry prepared in Example 6 and Comparative Example 6 of this invention. Detailed Implementation

[0033] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, provides a high-energy-density aqueous cathode slurry for lithium batteries, its preparation method, and its application. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0034] Example 1

[0035] S1: Mix anhydrous ethanol and deionized water in a volume ratio of 3:4;

[0036] S2: Weigh 0.5g xanthan gum and 30.0g of the solution prepared in step S1, and add them to a sealable stirring container. Stir and mix at room temperature.

[0037] S3: Weigh out 9.0g of lithium-rich manganese-based cathode material (Li(Li)). 0.116Ni 0.141 Co 0.136 Mn 0.547 Al 0.03 O2, LR270B and 0.5g Super P were added to the mixture prepared in step S2, and stirring was continued at 1000 rpm for 3 hours.

[0038] S4: The slurry prepared in step S3 is coated onto aluminum foil using a scraping method, with a coating thickness of 1000 micrometers.

[0039] S5: Place the coated electrode sheet from step S4 in a constant temperature drying oven for drying. The temperature-time curve is set as follows: 40℃ for 60 min; 60℃ for 60 min; 80℃ for 120 min.

[0040] S6: Then cut the electrode sheet prepared in step S5 into a circular sheet with a diameter of 14 mm, weigh it, and place it in a vacuum dryer at 100°C for 6 hours. Then take it out and put it in a glove box for later use.

[0041] Example 2

[0042] The positive electrode was prepared according to the preparation process of Example 1, except that 0.5g xanthan gum was replaced with 0.4g xanthan gum and 0.1g polyethylene glycol.

[0043] Example 3

[0044] The positive electrode was prepared according to the preparation process of Example 2, except that polyethylene glycol was replaced with sodium carboxymethyl cellulose.

[0045] Example 4

[0046] The positive electrode was prepared according to the preparation process of Example 2, except that polyethylene glycol was replaced with sodium alginate.

[0047] Example 5

[0048] The positive electrode was prepared according to the preparation process of Example 2, except that polyethylene glycol was replaced with polyethylene oxide.

[0049] Example 6

[0050] The cathode was prepared according to the preparation process of Example 1, except that the lithium-rich manganese-based cathode material LR270B was replaced with another lithium-rich manganese-based cathode material (Li(Li)). 0.147 Ni 0.137 Co 0.139 Mn 0.540 Al 0.002 O2, LR300).

[0051] Comparative Example 1

[0052] The positive electrode was prepared according to the preparation process of Example 1, except that anhydrous ethanol was replaced with n-propanol.

[0053] Comparative Example 2

[0054] The positive electrode was prepared according to the preparation process of Example 1, except that anhydrous ethanol was replaced with acetone.

[0055] Comparative Example 3

[0056] The positive electrode was prepared according to the preparation process of Example 1, except that the coating thickness was adjusted to 350 μm.

[0057] Comparative Example 4

[0058] The positive electrode was prepared according to the preparation process of Example 1, except that the coating thickness was adjusted to 150 μm.

[0059] Comparative Example 5

[0060] 90 parts by weight of lithium-rich manganese-based layered oxide (Li(Li) 0.116 Ni 0.141 Co 0.136 Mn 0.547 Al 0.03 5 parts by weight of O2, LR270B), 5 parts by weight of Super P conductive material, and 5 parts by weight of polyvinylidene fluoride (PVDF) binder are mixed and dispersed in N-methylpyrrolidone solvent, wherein the ratio of positive electrode active material to solvent is 8g:14mL, to obtain electrode slurry.

[0061] The above slurry was then coated onto aluminum foil, with the coating thickness adjusted to 300 μm. After the same drying process as in Example 1, it was cut into 14 mm round pieces and placed in a glove box for later use.

[0062] Comparative Example 6

[0063] The cathode was prepared following the same procedure as in Comparative Example 5, except that the lithium-rich manganese-based cathode material LR270B was replaced with another lithium-rich manganese-based cathode material (Li(Li)). 0.147 Ni 0.137 Co 0.139 Mn 0.540 Al 0.002 O2, LR300).

[0064] Lithium battery assembly:

[0065] The positive electrode, polyethylene separator, and lithium foil (16 mm in diameter and 1 mm in thickness) are sequentially stacked, and an appropriate amount of electrolyte (1 M LiPF6 solution; solvent EC:EMC:DMC (volume ratio 1:1:1)) is injected. After being packaged by a button cell packaging machine, a 2032 button cell is made.

[0066] Lithium battery testing:

[0067] (1) First discharge capacity and initial coulombic efficiency: Under constant current and constant voltage charging at an ambient temperature of 25℃, a voltage range of 2.0-4.8V, and a test current of 0.1C (1C, 250mA / g), the battery was charged to the upper voltage limit, and then discharged to the lower voltage limit at a constant current of 0.1C. The first discharge specific capacity and the ratio of the first discharge capacity to the charging capacity were recorded.

[0068] (2) Initial capacity test: At an ambient temperature of 25℃, a voltage range of 2.0-4.6V, and a test current of 0.1C (1C, 250mA / g), the battery was charged to the upper voltage limit using a constant current and constant voltage charging method. Then, it was discharged to the lower voltage limit using a constant current of 0.1C. The battery was subjected to 3 cycles to stabilize it, and the discharge capacity of the 3rd cycle was taken as the initial capacity.

[0069] (3) Cyclic test: For batteries that have undergone initial charge and discharge, 100 cycles are performed at 25°C as follows: voltage range 2.0-4.6V, charging to the upper voltage limit with a constant current and constant voltage of 1C, and then discharging to the lower voltage limit with a constant current of 1C. The ratio of the discharge capacity of the 100th cycle to the discharge capacity of the 1st cycle is taken as the cycle retention rate.

[0070] The test results are shown in Table 1:

[0071] Table 1. Electrochemical performance test results of the examples and comparative examples.

[0072]

[0073]

[0074] As shown in Table 1, comparing Examples 1-5 with Comparative Examples 1-2, it is evident that ethanol is more effective than n-propanol and acetone in the aqueous binder solution provided by this invention. Comparing Example 1 with Comparative Examples 3-4, it is evident that the electrode prepared from the aqueous positive electrode slurry provided by this invention has adjustable coating thickness and good performance consistency. Comparing Examples 1-6 with Comparative Examples 5-6, it is evident that using the aqueous positive electrode slurry provided by this invention can improve the initial coulombic efficiency of lithium batteries, reduce irreversible capacity loss, and thus improve the cycle retention rate of the battery.

[0075] Figure 1The first charge-discharge capacity-voltage curves (0.1C, 2.0-4.6V) of batteries using the positive electrode slurry prepared in Examples 1, 3 and 4 of this invention.

[0076] Figure 2 The first charge-discharge curves (0.1C, 2.0-4.8V) of the batteries using the positive electrode slurry prepared in Example 1 and Comparative Example 5 of this invention.

[0077] Figure 3 The first charge-discharge curves (0.1C, 2.0-4.8V) of the batteries using the positive electrode slurry prepared in Example 6 and Comparative Example 6 of this invention.

[0078] Depend on Figure 1 , Figure 2 and Figure 3 In summary, the aqueous cathode slurry provided by this invention is superior to the slurry prepared with oil-based binders, and the coating area can be increased, making it suitable for coating processes of high-energy-density batteries.

[0079] The electrode prepared by the aqueous slurry process provided in this invention contains xanthan gum. Therefore, Fourier transform infrared spectroscopy (FT-IR) can be used to quickly detect whether there is any infringement in the positive electrode coating process. The FT-IR characteristic peak of xanthan gum is: -OH (3433 cm⁻¹). -1 1157cm -1 1068cm -1 ), -C=O(1734cm) -1 ), -COO - (1624cm -1 1412cm -1 When the positive electrode active material is a lithium-rich manganese-based positive electrode material (Example 1), some values ​​shift to lower wavenumbers, such as -COO. - (1612cm -1 1407cm -1 Furthermore, if any one of the components—ethanol, n-propanol, and acetone—can be detected in the aqueous cathode slurry using gas / liquid chromatography, it can be determined as an infringement.

[0080] As can be seen from the above embodiments, the present invention provides a high-energy-density lithium battery aqueous positive electrode slurry, comprising a positive electrode active material, a conductive agent, a binder, and a mixed solvent in a mass ratio of (85-95):)(1-8):(1-8):(200-400); the binder comprises a first binder and a second binder in a mass ratio of 50-100:0-50; the first binder is xanthan gum; the second binder is selected from one or more of polyethylene oxide, polyethylene glycol, sodium alginate, and sodium carboxymethyl cellulose; the mixed solvent is a mixture of water and a polar organic solvent; the polar organic solvent is selected from one or more of ethanol, n-propanol, and acetone. The aqueous positive electrode slurry provided by this invention uses an aqueous dispersion system with a mixture of water and polar organic solvent as a binder. In the above mixed solvent, the molecular chain of the binder xanthan gum can be elongated and its morphology can be varied, which can better encapsulate and connect the positive electrode active material and the conductive agent. The above binder is stable to the electrolyte and does not swell, which can effectively reduce the side reactions between the electrolyte and the positive electrode active material, thereby improving the first coulombic efficiency of the battery and increasing the cycle life of the battery.

[0081] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-energy-density lithium battery aqueous positive electrode slurry, comprising a positive electrode active material, a conductive agent, a binder, and a mixed solvent in a mass ratio of (85-95):(1-8):(1-8):(200-400); The adhesive comprises a first adhesive and a second adhesive in a mass ratio of 50-100:0-50; The first adhesive is xanthan gum; The second adhesive is selected from one or more of polyethylene oxide, polyethylene glycol, sodium alginate, and sodium carboxymethyl cellulose; The mixed solvent is a mixture of water and a polar organic solvent; the polar organic solvent is selected from one or more of ethanol, n-propanol and acetone.

2. The high-energy-density lithium battery aqueous cathode slurry according to claim 1, characterized in that, The polar organic solvent accounts for 10-60% of the water by mass.

3. The high-energy-density lithium battery aqueous cathode slurry according to claim 1, characterized in that, The relative molecular weight of the second adhesive is 1×10⁻⁶. 4 ~2×10 6 ; The relative molecular weight of the xanthan gum is 1×10⁻⁶. 5 ~2×10 8 .

4. The high-energy-density lithium battery aqueous cathode slurry according to claim 1, characterized in that, The positive electrode active material is selected from lithium-rich manganese-based matrix oxides having the composition of Formula I: x Li2MnO3.(1-x)LiMO2 Formula I; M is a transition metal, such as Ni, Co, or Mn, and 0.1 <x<0.7。 5. The high-energy-density lithium battery aqueous cathode slurry according to claim 1, characterized in that, The conductive agent is selected from one or more of acetylene black, Super P, graphene, carbon nanotubes, and Ketjen black.

6. A method for preparing the high-energy-density lithium battery aqueous cathode slurry according to any one of claims 1 to 5, comprising the following steps: The first and second binders are dissolved in a mixed solvent, and then a conductive agent and positive electrode active material are added and mixed to obtain a high-energy-density lithium battery aqueous positive electrode slurry.

7. A high-energy-density lithium battery aqueous positive electrode sheet, prepared by coating the aqueous positive electrode slurry according to any one of claims 1 to 5 onto a current collector and drying it.

8. The high-energy-density lithium battery aqueous positive electrode sheet according to claim 7, characterized in that, The coating thickness is 100–2000 micrometers.

9. A lithium battery comprising the high-energy-density aqueous positive electrode, negative electrode, separator, and electrolyte as described in any one of claims 7 to 8.

10. The lithium battery according to claim 9, characterized in that, The negative electrode is selected from graphite, silicon, or lithium foil; The lithium battery type is selected from button cells, pouch cells, 18650 cells, or square aluminum-cased cells.

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