Modified manganese dioxide positive electrode for lithium primary battery and preparation method of modified manganese dioxide positive electrode

Abstract

The invention discloses a modified manganese dioxide positive electrode for a lithium primary battery and a preparation method of the modified manganese dioxide positive electrode, and belongs to the technical field of primary batteries. Manganese dioxide and conductive carbon black (SP) dry powder are sequentially added into a ball milling tank, the mass ratio of SP is 3-10%, the mass ratio of manganese dioxide is 90-97%, and the dry powder is evenly mixed through a ball mill. The preparation method comprises the following steps: stirring polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP) and polypropylene (PP) according to a ratio by taking deionized water as a medium, taking ammonium perfluorooctanoate as an emulsifier and taking persulfate as an initiator to enable monomers to be subjected to polymerization reaction so as to prepare a PFP emulsion; the obtained PFP emulsion is added into the powder, the mass of the PFP emulsion accounts for 1-5% of the mass of the powder, meanwhile, deionized water is added to adjust the solid content of the slurry to be 20-40%, and the slurry is mixed to be uniform through a ball mill. The homogenizing method has the characteristics of simplicity in operation, convenience and rapidness, and the discharge capacitance of the lithium manganese dioxide battery can be effectively improved by the homogenizing method.

Description

Technical Field

[0001] The invention belongs to the technical field of primary batteries, and in particular relates to a modified manganese dioxide positive electrode for a lithium primary battery and a preparation method thereof. Background Art

[0002] Lithium primary batteries with metallic lithium as the negative electrode have the advantages of high specific energy, long storage life, high platform voltage, and wide operating temperature range, and play a vital role in today's energy storage field.

[0003] Lithium manganese dioxide battery is an organic electrolyte lithium primary battery with lithium as the negative electrode and manganese dioxide as the positive electrode. During discharge, the lithium negative electrode undergoes an oxidation reaction to produce lithium ions, which migrate to the manganese dioxide positive electrode and embed into its lattice, and the manganese element is reduced from tetravalent to trivalent. During the winding process of the fully sealed cylindrical battery, the positive electrode sheet of the battery is prone to "material dropout" due to factors such as the uniformity of the size and shape of the manganese dioxide particles, the degree of compaction, and the binder. The dropped positive electrode material accumulates inside the battery, destroying the diaphragm material between the positive and negative electrodes, causing a micro-short circuit inside the battery, generating a lot of heat inside the battery, causing the battery to bulge and leak, leading to problems such as reduced battery capacity, voltage drop, and shortened cycle life. The positive electrode material of the cylindrical battery is longer and requires production processes such as winding, which makes it more likely to cause the positive electrode sheet material to fall off. Summary of the invention

[0004] The purpose of the present invention is to provide a modified manganese dioxide positive electrode for a lithium primary battery and a preparation method thereof, wherein a high-viscosity binder is used to modify the manganese dioxide positive electrode to improve the electrochemical performance of the lithium manganese dioxide battery.

[0005] The technical solution adopted by the present invention is: a method for preparing a modified manganese dioxide positive electrode for a lithium primary battery, comprising the following steps:

[0006] Step 1: Add manganese dioxide and conductive carbon black SP dry powder into a ball mill, wherein the mass proportion of SP is 3%-10% and the mass proportion of manganese dioxide is 90%-97%, and mix the dry powders evenly using a ball mill;

[0007] Step 2, adding polytetrafluoroethylene PTFE, polyperfluoroethylene propylene FEP, and polypropylene PP into deionized water in a mass ratio of (1-5): (0.5-1.5): 1, adding an emulsifier and an initiator, stirring, allowing the monomers to undergo polymerization reaction, and obtaining a PFP emulsion through cooling, washing, drying, grinding, and classification, wherein the solid content of the PFP emulsion is 10%-50%;

[0008] Step 3: Add the PFP emulsion obtained in step 2 to the powder in step 1, the mass of the PFP emulsion is 1%-5% of the mass of the powder in step 1, and deionized water is added to adjust the solid content of the slurry to 20%-40%, and mix evenly with a ball mill.

[0009] In step 1, the specific surface area of ​​the SP is 20-100m 2 / g, ball milling time is 1.5-2h.

[0010] In the step 2, the molecular weight of the PTFE used is 5000-20000, the molecular weight of the FEP is 200000-600000, the molecular weight of the PP is 80000-150000, the stirring speed is 10-300r / min, and the stirring time is 12-24h, until a stable and uniform colloid is generated in the deionized water.

[0011] In the step 3, the ball mill rotates at a speed of 250-500 r / min and the ball milling time is 9-12 h until a uniform fluid is generated.

[0012] In the step 2, the emulsifier is ammonium perfluorooctanoate and the initiator is persulfate.

[0013] The preparation process was carried out at 25°C and relative humidity ≤ 1%.

[0014] The modified manganese dioxide positive electrode for lithium primary battery prepared by the above preparation method.

[0015] The present invention has the following advantages and positive effects:

[0016] 1. The present invention selects SP with excellent conductivity, good dispersibility and high stability as the electrode conductive agent to ensure the high conductivity of the electrode. On this basis, SP with a suitable specific surface area is selected to prevent SP from agglomerating in the slurry. The rough surface is conducive to mixing with other materials and enhances its dispersibility in the slurry. On the other hand, SP has a certain liquid absorption and retention effect, which is conducive to the adsorption of electrolytes, thereby enhancing the ionic conductivity of the battery system.

[0017] 2. The present invention is simple to operate and easy to prepare.

[0018] 3. The present invention selects PTFE, FEP and PP as the main components of the binder. PTFE has good heat resistance and strong corrosion resistance; FEP has good thermal stability and good processing performance; PP has good tensile strength and resistance to environmental stress cracking. The binder prepared on this basis has good chemical stability and can tightly bond the manganese dioxide particles together to prevent the particles from falling off during production and charging and discharging. In addition, under the bonding effect, the manganese dioxide is tightly connected to the SP to form a continuous conductive path; on the other hand, the presence of the binder can adjust the void structure of the positive electrode sheet, which is beneficial to the migration of ions in the electrode / electrolyte cross section, while promoting the uniformity of the electrode sheet and facilitating the wetting of the electrolyte. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention is further described in detail. It should be understood that the specific implementation methods described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] A method for preparing a modified manganese dioxide positive electrode for a lithium primary battery of the present invention comprises the following steps:

[0021] Step 1: Add manganese dioxide and conductive carbon black SP dry powder into a ball mill, wherein the mass proportion of SP is 3%-10% and the mass proportion of manganese dioxide is 90%-97%, and mix the dry powders evenly using a ball mill;

[0022] Step 2, adding polytetrafluoroethylene PTFE, polyperfluoroethylene propylene FEP, and polypropylene PP into deionized water in a mass ratio of (1-5): (0.5-1.5): 1, adding an emulsifier and an initiator, stirring, allowing the monomers to undergo polymerization reaction, and obtaining a PFP emulsion through cooling, washing, drying, grinding, and classification, wherein the solid content of the PFP emulsion is 10%-50%;

[0023] Step 3: Add the PFP emulsion obtained in step 2 to the powder in step 1, the mass of the PFP emulsion is 1%-5% of the mass of the powder in step 1, and deionized water is added to adjust the solid content of the slurry to 20%-40%, and mix evenly with a ball mill.

[0024] In step 1, the specific surface area of ​​the SP is 20-100m 2 / g, ball milling time is 1.5-2h.

[0025] In the step 2, the molecular weight of the PTFE used is 5000-20000, the molecular weight of the FEP is 200000-600000, the molecular weight of the PP is 80000-150000, the stirring speed is 10-300r / min, and the stirring time is 12-24h, until a stable and uniform colloid is generated in the deionized water.

[0026] In the step 3, the ball mill rotates at a speed of 250-500 r / min and the ball milling time is 9-12 h until a uniform fluid is generated.

[0027] In the step 2, the emulsifier is ammonium perfluorooctanoate and the initiator is persulfate.

[0028] The preparation process was carried out at 25°C and relative humidity ≤ 1%.

[0029] The modified manganese dioxide positive electrode for lithium primary battery prepared by the above preparation method.

[0030] The content, features and effects of the present invention are described in detail below. Here are some examples, which are described in detail as follows:

[0031] Example 1

[0032] Step 1: Add 142.5g of manganese dioxide and 7.5g of conductive carbon black (SP) dry powder into the ball mill, where the mass proportion of SP is 5% and the specific surface area is 60m 2 / g, the mass proportion of manganese dioxide is 95%, and the ball milling time is 1.5h.

[0033] Step 2: Add 3g polytetrafluoroethylene (PTFE), 1g polyperfluoroethylene propylene (FEP), and 1g polypropylene (PP) in a ratio of 3:1:1 to 11.67g deionized water, the molecular weight of PTFE is 5000, the molecular weight of FEP is 200000, and the molecular weight of PP is 80000. Add 0.025g emulsifier and 0.005g initiator, the magnetic rotor speed is 100r / min, the stirring time is 12h, until the polymer forms a uniform and stable colloid in deionized water, and adjust the solid content of PFP emulsion to 30%.

[0034] Step 3: Take 4.5g of the PFP emulsion obtained in step 2 and add it to the powder in step 1. The mass of the PFP emulsion is 3% of the mass of the powder in step 1. At the same time, add 350g of deionized water to adjust the solid content of the slurry to 30%. Mix it evenly with a ball mill at a speed of 250r / min for 9h until a uniform fluid is generated.

[0035] The viscosity of the slurry was tested using a rotational viscometer. The positive electrode materials were assembled into simulated cylindrical batteries, the batteries were discharged at a constant current, and the discharge capacity of the batteries was recorded.

[0036] Example 2

[0037] Step 1: Add 135g of manganese dioxide and 15g of conductive carbon black (SP) dry powder into the ball mill, where the mass proportion of SP is 10% and the specific surface area is 100m 2The mass proportion of manganese dioxide / g is 90%, and the ball milling time is 2h.

[0038] Step 2: Add 1.25g polytetrafluoroethylene (PTFE), 0.125g polyperfluoroethylene propylene (FEP), and 0.25g polypropylene (PP) in a ratio of 5:0.5:1 to 14.625g deionized water, add 0.008g emulsifier and 0.0016g initiator, the molecular weight of PTFE is 20000, the molecular weight of FEP is 600000, the molecular weight of PP is 150000, the speed of the magnetic rotor is 300r / min, the stirring time is 24h, until the polymer forms a uniform and stable colloid in deionized water, and the solid content of the PFP emulsion is adjusted to 10%.

[0039] Step 3: Take 7.5g of the PFP emulsion obtained in step 2 and add it to the powder in step 1. The mass of the PFP emulsion is 5% of the mass of the powder in step 1. At the same time, add 219.375g of deionized water to adjust the solid content of the slurry to 40%. Mix it evenly with a ball mill at a speed of 500r / min and a ball milling time of 12h until a uniform fluid is generated.

[0040] The viscosity of the slurry was tested using a rotational viscometer. The positive electrode materials were assembled into simulated cylindrical batteries, the batteries were discharged at a constant current, and the discharge capacity of the batteries was recorded.

[0041] Example 3

[0042] Step 1: Add 145.5g of manganese dioxide and 4.5g of conductive carbon black (SP) dry powder into the ball mill, where the mass proportion of SP is 3% and the specific surface area is 20m 2 The mass proportion of manganese dioxide / g is 97%, and the ball milling time is 1.5h.

[0043] Step 2: Add 1g of polytetrafluoroethylene (PTFE), 1.5g of polyperfluoroethylene propylene (FEP), and 1g of polypropylene (PP) to 3.5g of deionized water in a ratio of 1:1.5:1. The molecular weight of PTFE is 5000, the molecular weight of FEP is 200000, and the molecular weight of PP is 80000. Add 0.0175g of emulsifier and 0.0035g of initiator. The magnetic rotor speed is 100r / min and the stirring time is 12h until the polymer forms a uniform and stable colloid in deionized water. Adjust the solid content of the PFP emulsion to 50%.

[0044] Step 3: Take 1.5g of the PFP emulsion obtained in step 2 and add it to the powder in step 1. The mass of the PFP emulsion is 1% of the mass of the powder in step 1. At the same time, add 602.25g of deionized water to adjust the solid content of the slurry to 20%. Mix it evenly with a ball mill at a speed of 250r / min for 9h until a uniform fluid is generated.

[0045] The viscosity of the slurry was tested using a rotational viscometer. The positive electrode materials were assembled into simulated cylindrical batteries, the batteries were discharged at a constant current, and the discharge capacity of the batteries was recorded.

[0046] Experimental Results

[0047] The viscosity of the lithium manganese dioxide electrode slurry prepared in Example 1-3 after being stirred at a low speed in a homogenizer for 4 hours is shown in Table 1.

[0048] Table 1 shows the viscosity change of the slurry obtained by the method of the present invention

[0049] Homogenization method Viscosity / mPa·s Example 1 9651 Example 2 9926 Example 3 9517 Conventional homogenization method 7763

[0050] The slurry prepared in Example 1-3 has a higher viscosity after stirring at a low speed for 4 hours than the slurry obtained by the conventional homogenization method.

[0051] The constant current discharge capacity of the lithium manganese dioxide batteries prepared in Examples 1-3 is shown in Table 2.

[0052] Table 2 shows the capacity of the battery produced by the method of the present invention.

[0053] Homogenization method Discharge capacity / Ah Example 1 3.1692 Example 2 3.1602 Example 3 3.1635 Conventional homogenization method 3.1396

[0054] It can be seen from Table 2 that the lithium manganese dioxide battery obtained by the method of Example 1 has a larger capacity than the battery obtained by the conventional homogenization method. This is because the addition of the new binder enhances the adhesion of the positive electrode material, reduces the shedding of the positive electrode material during production and discharge, and the path for ion diffusion inside the material is unobstructed, thereby avoiding the formation of micro-short circuits inside the battery, thereby increasing the capacity of the battery.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a modified manganese dioxide positive electrode for a lithium primary battery, characterized in that: The following steps are involved: Step 1: Add manganese dioxide and conductive carbon black SP dry powder into a ball mill, wherein the mass proportion of SP is 3%-10% and the mass proportion of manganese dioxide is 90%-97%, and mix the dry powders evenly using a ball mill; Step 2, adding polytetrafluoroethylene PTFE, polyperfluoroethylene propylene FEP, and polypropylene PP into deionized water in a mass ratio of (1-5): (0.5-1.5): 1, adding an emulsifier and an initiator, stirring, allowing the monomers to undergo polymerization reaction, and obtaining a PFP emulsion through cooling, washing, drying, grinding, and classification, wherein the solid content of the PFP emulsion is 10%-50%; Step 3: Add the PFP emulsion obtained in step 2 to the powder in step 1, the mass of the PFP emulsion is 1%-5% of the mass of the powder in step 1, and deionized water is added to adjust the solid content of the slurry to 20%-40%, and mix evenly with a ball mill.

2. The method for preparing a modified manganese dioxide positive electrode for a lithium primary battery according to claim 1, characterized in that: In step 1, the specific surface area of ​​the SP is 20-100m 2 / g, ball milling time is 1.5-2h.

3. The method for preparing a modified manganese dioxide positive electrode for a lithium primary battery according to claim 1, characterized in that: In the step 2, the molecular weight of the PTFE used is 5000-20000, the molecular weight of the FEP is 200000-600000, the molecular weight of the PP is 80000-150000, the stirring speed is 10-300r / min, and the stirring time is 12-24h, until a stable and uniform colloid is generated in the deionized water.

4. The method for preparing a modified manganese dioxide positive electrode for a lithium primary battery according to claim 1, characterized in that: In the step 3, the ball mill rotates at a speed of 250-500 r / min and the ball milling time is 9-12 h until a uniform fluid is generated.

5. The method for preparing a modified manganese dioxide positive electrode for a lithium primary battery according to claim 1, characterized in that: In the step 2, the emulsifier is ammonium perfluorooctanoate and the initiator is persulfate.

6. The method for preparing a modified manganese dioxide positive electrode for a lithium primary battery according to claim 1, characterized in that: The preparation process was carried out at 25°C and relative humidity ≤ 1%.

7. A modified manganese dioxide positive electrode for a lithium primary battery obtained by the preparation method according to any one of claims 1 to 6.