Oil-based homogenizing method for power lithium primary battery positive electrode slurry

Abstract

This invention relates to an oil-based homogenization method for power lithium primary batteries. The positive electrode slurry is prepared using a solvent with a low DN value and a highly conductive and high specific surface area conductive agent. The positive electrode slurry comprises electrolytic manganese dioxide, high-power fluorinated carbon, VC (Cabot conductive carbon), low aspect ratio vapor-grown carbon fiber reinforcement (VGCF), polyvinylidene fluoride (PVDF), and a solvent with a low DN value. By selecting the solvent and conductive agent, PVDF can be effectively dissolved while avoiding side reactions between the carbon-fluorine half-ionic bonds in the manganese dioxide-high-power fluorinated carbon composite material and the solvent during the homogenization process.

Description

Technical Field

[0001] This invention belongs to the field of lithium primary battery technology, and in particular relates to an oil-based homogenization method for positive electrode slurry of power lithium primary batteries. Background Technology

[0002] Lithium-manganese dioxide (MnO) batteries are widely used in lithium primary battery systems due to their high specific energy and low cost. However, their poor electronic conductivity leads to poor reaction kinetics, resulting in severe voltage hysteresis and capacity decay at low temperatures. Furthermore, their poor ion and electron transport characteristics and high manganese-oxygen bond energy also contribute to the poor Mn content at the interface. 4+ →Mn 2+ The two-electron transfer reaction is difficult to occur, thus limiting the specific capacity of manganese dioxide to 308 mAh / g.

[0003] Fluorocarbon materials currently boast the highest theoretical specific energy among solid electrode materials, reaching up to 2200 Wh / kg. Furthermore, the carbon in its discharge products exhibits excellent electronic conductivity, effectively enhancing electrode conductivity. However, the high bond energy of the carbon-fluorine bond results in a significant energy barrier for bond breaking and relatively low conductivity, impacting the power characteristics of fluorocarbon materials. For high-power fluorocarbon materials, employing a common oil-based slurry process can lead to a substantial decrease in specific energy. This is primarily because the commonly used solvent NMP (N,N-dimethylpyrrolidone) has a high DN value, inducing spontaneous dissociation of the carbon-fluorine half-ionic bonds, thus causing a significant drop in specific energy. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides an oil-based homogenization method for positive electrode slurry of power lithium primary batteries.

[0005] The technical solution adopted in this invention is: an oil-based homogenization method for positive electrode slurry of power lithium primary batteries, the specific preparation method of which is as follows:

[0006] Step 1: Mix electrolytic manganese dioxide, high-power fluorinated carbon, VC (Cabot conductive carbon), and low aspect ratio VGCF.

[0007] Step 2: Dissolve PVDF in a solvent with a low DN value, and heat and stir until completely dissolved;

[0008] Step 3: Add the PVDF solution prepared in Step 2 to the powder obtained in Step 1, add a solvent with a low DN value, mix to form a fluid, and obtain the positive electrode slurry;

[0009] The components are: electrolytic manganese dioxide (50-70 parts by mass), high-power fluorinated carbon (20-40 parts by mass), VC (3-5 parts by mass), low aspect ratio VGCF (2-5 parts by mass), and PVDF (4-5 parts by mass).

[0010] Preferably, the low DN value solvent includes one or two of TEP (triethyl phosphate), TMP (trimethyl phosphate), and DMF (dimethylformamide).

[0011] Preferably, the F / C ratio of the high-power fluorocarbon is less than or equal to 0.8, and the specific surface area of ​​the VC is greater than 1200 m². 2 / g, VGCF has an aspect ratio of less than or equal to 100, and PVDF has a molecular weight of 350,000-450,000.

[0012] Preferably, in step one, the mixture is mixed using a ball mill, with the ball mill speed being 350-450 r / min and the ball milling time being 12-20 h;

[0013] In step three, the slurry is mixed using a ball mill at a speed of 300-500 r / min for 10-12 hours.

[0014] Preferably, the homogenization process is carried out in a drying room with a dew point temperature not higher than -40°C.

[0015] A battery positive electrode is prepared from a positive electrode slurry obtained by an oil-based homogenization method for preparing positive electrode slurry of a power lithium primary battery.

[0016] A power-type lithium primary battery, comprising the above-mentioned positive electrode.

[0017] The advantages and positive effects of this invention are: using a low DN value solvent for homogenization avoids side reactions between carbon-fluorine half-ionic bonds in high-power fluorocarbon materials. Due to the high boiling point of the solvent, the slurry has a good state retention rate in the drying room, reducing the sedimentation rate of the slurry. Therefore, the active material on the electrode is evenly distributed during coating, ensuring a high specific capacity retention rate of the high-power fluorocarbon material.

[0018] The use of composite conductive agents constructs a three-dimensional conductive network, which greatly improves the electronic conductivity of the electrodes. The use of high specific surface area VC improves the wettability of the electrolyte to the electrodes, and the use of low aspect ratio VGCF enables dual conduction of ions and electrons, thereby improving the rate performance of the battery. Attached Figure Description

[0019] Figure 1 XRD patterns of high-power fluorocarbon materials before and after immersion;

[0020] Figure 2SEM images of bifunctional conductive VGCF

[0021] Figure 3 TEM image of bifunctional conductive VGCF

[0022] Figure 4 Optical images of the electrode sheet prepared in Example 1;

[0023] Figure 5 The discharge curve of a lithium-manganese dioxide battery;

[0024] Figure 6 The 2p Mn element spectrum of XPS obtained after electrode discharge in Example 1 is shown. Detailed Implementation

[0025] The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0026] This invention relates to an oil-based homogenization method for a positive electrode slurry in a power lithium primary battery. The positive electrode slurry is prepared using a solvent with a low density (DN) value and a highly conductive and high specific surface area conductive agent. The slurry comprises electrolytic manganese dioxide, high-power fluorinated carbon, VC (Cabot conductive carbon), low aspect ratio vapor-grown carbon fiber reinforcement (VGCF), polyvinylidene fluoride (PVDF), and a solvent with a low DN value. By selecting the appropriate solvent and conductive agent, PVDF can be effectively dissolved while avoiding side reactions between the carbon-fluorine half-ionic bonds in the manganese dioxide-high-power fluorinated carbon composite material and the solvent during homogenization.

[0027] The specific surface area of ​​the VC used in preparing the positive electrode slurry is greater than 1200 m². 2 / g, the aspect ratio of the low aspect ratio VGCF used is ≤100, the F / C ratio of the high power fluorinated carbon used is ≤0.8 and has a porous structure; the molecular weight of the PVDF used is 350,000-450,000, and the solvent with a low DN value used includes one or more of TEP (triethyl phosphate), TMP (trimethyl phosphate), and DMF (dimethylformamide).

[0028] The specific homogenization method for the positive electrode slurry is as follows:

[0029] Step 1: Add the dry powders of electrolytic manganese dioxide, high-power fluorocarbon, vitamin C, and VGCF sequentially into a ball mill jar. The mass percentage of electrolytic manganese dioxide is 50%-70%, the mass percentage of high-power fluorocarbon is ≥20%, the mass percentage of vitamin C is 3%-5%, and the mass percentage of low aspect ratio VGCF is 2%-5%. Mix the dry powders evenly using a ball mill. The discharge voltage plateau should be ≥ the discharge voltage plateau of manganese dioxide. The rotation speed of the ball mill is 350-450 r / min, and the milling time is 12-20 h.

[0030] Step 2: Dissolve PVDF powder in a solvent with a lower DN value, heat it at 45°C using a heating table, and stir it with a magnetic stir bar at a speed of 700-900 r / min for 18-24 h until PVDF is completely dissolved in the solvent with a lower DN value to form a homogeneous and stable colloid with a PVDF mass fraction of 6%-8%.

[0031] Step 3: Add the PVDF solution prepared in Step 2 to the powder obtained in Step 1, with the mass ratio of PVDF being 5%; add the same solvent with a lower DN value to the mixture to adjust the solid content of the slurry to 30%-40%, and use a ball mill to mix the slurry evenly at a speed of 300-500 r / min for 10-12 h until the final mixture becomes a uniform fluid, thus obtaining the battery positive electrode slurry.

[0032] The above preparation process is carried out in a drying room with a dew point temperature not exceeding -40℃. The battery positive electrode slurry prepared by the above method is coated on aluminum foil to further prepare a power-type lithium primary battery.

[0033] By selecting a solvent with a low DN value, side reactions between NMP in commonly used homogenization methods and the carbon-fluorine half-ionic bonds in high-power fluorocarbon materials are avoided. For example... Figure 1 The figures show the XRD patterns of the original high-power fluorocarbon material and the high-power fluorocarbon material after soaking in DMSO, TEP (a solvent with a lower DN value), and NMP, respectively. The characteristic peaks of the high-power fluorocarbon material hardly shifted after treatment with the lower DN value solvent, indicating that the material structure remained unchanged. The material structure changed after using the high DN value solvents NMP and DMSO, indicating the occurrence of side reactions. The lower DN value solvent ensured a high specific capacity retention rate of the high-power fluorocarbon material. Simultaneously, due to the high boiling point of the solvent, the slurry maintained a good state retention rate in the drying chamber, reducing the sedimentation rate of the slurry and thus ensuring uniform distribution of active material on the electrode during coating.

[0034] The use of composite conductive agents constructed a three-dimensional conductive network, which greatly improved the electronic conductivity of the electrode. SEM and TEM images of VGCF were obtained. Figure 2-3 It can be seen that VGCF has a low aspect ratio, thus achieving dual transport characteristics of electron conduction along the carbon nanotube surface and ion conduction along the tube. The use of high specific surface area VC improves the wettability of the electrolyte to the electrode, while the use of low aspect ratio VGCF achieves dual conduction of ions and electrons, thereby improving the rate performance of the battery.

[0035] By combining high-power fluorinated carbon with manganese dioxide, synergistic discharge of the two compounds was achieved, promoting the controllable occurrence of the manganese dioxide disproportionation reaction at the interface and realizing the two-electron transfer reaction of manganese dioxide. Firstly, the carbon-fluorine half-ionic bonds of the high-power fluorinated carbon exhibit higher reactivity, which is particularly beneficial during ball milling of CF2. x F-Mn bonds are formed at the MnO2 interface, thereby enhancing the electrochemical activity of Mn and promoting Mn oxidation. 3+ The generation of MnO2, along with the strong electronegativity of F, allows it to weaken the bond energy of manganese-oxygen bonds through supramolecular interactions, thereby promoting the interfacial disproportionation reaction. Secondly, the high proportion of fluorinated carbon in the composite electrode ensures a high proportion of conductive carbon in the reaction products, promoting electron transport. Simultaneously, the high proportion of fluorinated carbon fully utilizes the expansion effect of fluorinated carbon materials to achieve "fluffing" of the electrode, promoting electrolyte wetting and shortening the lithium-ion diffusion path. The construction of a good ion and electron transport network lowers the reaction energy barrier of the interfacial disproportionation reaction, promoting its occurrence. This also ensures the full reaction of the disproportionation product MnO2. Furthermore, the porous conductive carbon generated by the fluorinated carbon reaction can effectively adsorb the Mn produced by the disproportionation reaction. 2+ This promotes the disproportionation reaction and prevents the reaction between lithium metal and Mn. 2+ Side effects.

[0036] By selecting high-power fluorinated carbon materials with low fluorination degree and high carbon-fluorine half-ionic bond content, the problem of high bond energy of carbon-fluorine bonds resulting in a large breaking energy barrier and low conductivity can be effectively improved. Combining high-power fluorinated carbon materials with manganese dioxide can effectively enhance the power characteristics and specific energy of manganese dioxide. Using TEP (triethyl phosphate) and TMP (trimethyl phosphate), which have low DN values, as new homogenization solvents can effectively avoid side reactions between carbon-fluorine half-ionic bonds and the solvent, thus ensuring the normal performance of the specific energy of the manganese dioxide-high-power fluorinated carbon composite material; thereby improving the rate performance and electrical performance of high-power lithium primary batteries.

[0037] The present invention will now be described with reference to the accompanying drawings. Experimental methods not specifically described in terms of operation steps are performed in accordance with the corresponding product manuals. Unless otherwise specified, the instruments, reagents, and consumables used in the embodiments can be purchased from commercial companies.

[0038] Example 1

[0039] The preparation of the battery positive electrode slurry includes the following steps.

[0040] Step 1: Add the dry powders of electrolytic manganese dioxide, high-power fluorinated carbon with a fluorine-to-carbon ratio of 0.6, vitamin C, and VGCF with an aspect ratio of 50 to a ball mill jar in sequence. The mass fractions of electrolytic manganese dioxide are 70, high-power fluorinated carbon is 20, vitamin C is 3, and VGCF is 2. Mix the dry powders evenly using a ball mill. The ball mill speed is 350 r / min, and the ball milling time is 15 h.

[0041] Step 2: Dissolve PVDF powder in TEP, heat at 45°C using a heating table, and stir with a magnetic stir bar at 700 r / min for 24 hours until PVDF is completely dissolved in TEP to form a homogeneous and stable colloid with a PVDF mass fraction of 6%.

[0042] Step 3: Add the PVDF solution prepared in Step 2 to the mixed powder obtained in Step 1. The mass fraction of PVDF is 5. Add TEP to the mixed system to adjust the solid content of the slurry to 30%. Use a ball mill to mix the slurry evenly. The ball mill speed is 300-500 r / min, and the stirring time is 10-12 h until the final mixture becomes a uniform fluid, which is the battery positive electrode slurry.

[0043] Example 2

[0044] The preparation of the battery positive electrode slurry includes the following steps.

[0045] Step 1: Add the dry powders of electrolytic manganese dioxide, fluorinated carbon with a fluorine-to-carbon ratio of 0.7, vitamin C, and VGCF with an aspect ratio of 50 to a ball mill jar in sequence. The mass fractions of electrolytic manganese dioxide are 60, high-power fluorinated carbon is 30, vitamin C is 4, and low aspect ratio VGCF is 5. Mix the dry powders evenly using a ball mill. The ball mill speed is 450 r / min, and the ball milling time is 12 h.

[0046] Step 2: Dissolve PVDF powder in TMP, heat it at 45°C using a heating table, and stir it with a magnetic stir bar at a speed of 900 r / min for 18 hours until PVDF is completely dissolved in TMP to form a homogeneous and stable colloid with a PVDF mass fraction of 6%.

[0047] Step 3: Add the PVDF solution prepared in Step 2 to the mixed powder obtained in Step 1. The mass fraction of PVDF is 5. Add TMP to the mixed system to adjust the solid content of the slurry to 35%. Use a ball mill to mix the slurry evenly. The ball mill speed is 300-500 r / min and the stirring time is 10-12 h until the final mixture becomes a uniform fluid, which is the battery positive electrode slurry.

[0048] Example 3

[0049] The preparation of the battery positive electrode slurry includes the following steps.

[0050] Step 1: Add the dry powders of electrolytic manganese dioxide, fluorinated carbon with a fluorine-to-carbon ratio of 0.65, vitamin C, and VGCF with an aspect ratio of 80 to a ball mill jar in sequence. The mass fractions of electrolytic manganese dioxide are 50, high-power fluorinated carbon is 40, vitamin C is 4, and low aspect ratio VGCF is 5. Mix the dry powders evenly using a ball mill. The ball mill speed is 400 r / min, and the ball milling time is 20 h.

[0051] Step 2: Dissolve PVDF powder in TEP:TMP (v:v=1:1), heat at 45°C using a heating table, and stir with a magnetic stir bar at 800 r / min for 20 h until PVDF is completely dissolved in TEP:TMP (v:v=1:1) to form a homogeneous and stable colloid with a PVDF mass fraction of 6%.

[0052] Step 3: Add the PVDF solution prepared in Step 2 to the mixed powder obtained in Step 1, with a PVDF mass fraction of 5; add TEP:TMP (v:v=1:1) to the mixed system to adjust the solid content of the slurry to 40%, and use a ball mill to mix the slurry evenly.

[0053] Comparative Example 1:

[0054] The battery cathode slurry was prepared according to the method in Example 1, except that the solvent type was changed. Specifically, in step two, N-methylpyrrolidone (NMP) was used instead of TEP, and in step three, NMP was added to the mixed system to adjust the solid content of the slurry.

[0055] Comparative Example 2:

[0056] The battery positive electrode slurry was prepared according to the method of Example 1, except that the mass percentage of high-power fluorinated carbon was adjusted to be less than 20%. Specifically, in step one, the mass percentage of electrolytic manganese dioxide in the powder mixture was 80, the mass percentage of high-power fluorinated carbon was 10, the mass percentage of VC was 3, and the mass percentage of VGCF was 2.

[0057] Comparative Example 3:

[0058] The battery cathode slurry was prepared according to the method of Example 1, except that a VGCF with an aspect ratio greater than 100 was used; specifically, in step one, dry powder of VGCF with an aspect ratio of 450 was used instead of dry powder of VGCF with an aspect ratio of 50.

[0059] Comparative Example 4:

[0060] The battery cathode slurry was prepared according to the method in Example 1, except that a fluorinated carbon material with a high fluorine-to-carbon ratio was used; specifically, an energy-type fluorinated graphite with a fluorine-to-carbon ratio of 1 was used instead of a high-power fluorinated carbon with a fluorine-to-carbon ratio of 0.6.

[0061] Example 4: Preparation of the positive electrode for a lithium-manganese dioxide battery

[0062] The positive electrode slurry prepared in Example 1 was coated onto aluminum foil, cut, and dried to obtain the positive electrode for a lithium-manganese dioxide battery, as shown below. Figure 4 The image shown is an optical image of a high-power fluorinated carbon electrode, which shows that the active material is uniformly distributed on the aluminum foil.

[0063] The slurries obtained in Example 1 and Comparative Examples 1-4 were respectively used to prepare battery positive electrodes, and combined with lithium metal negative electrodes to assemble lithium-manganese dioxide batteries. Each battery group was discharged at room temperature with a current density of 0.05C for testing. The results are as follows: Figure 5 As shown, compared to conventional oil-based homogenization methods (such as Comparative Example 1), the lithium-manganese dioxide battery prepared with the cathode slurry of Example 1 exhibits a higher discharge specific energy. This is mainly because the lower DN value solvent effectively avoids side reactions between the solvent and high-power fluorinated carbon, while the use of composite conductive agents constructs a three-dimensional conductive network, greatly improving the electronic conductivity of the electrode. Example 1 also shows a significant advantage in discharge specific energy compared to Comparative Examples 2-4. The use of high specific surface area VC improves the wettability of the electrolyte to the electrode, and the use of low aspect ratio VGCF achieves dual conduction of ions and electrons, thereby improving the rate performance of the battery. Furthermore, the synergistic reaction between high-power fluorinated carbon and manganese dioxide effectively improves the electrochemical activity utilization rate of manganese, realizes some dual electron transfer reactions of manganese dioxide, and improves the discharge specific capacity of manganese dioxide.

[0064] The positive electrode sheet containing the positive electrode slurry of Example 1 after discharge was subjected to XPS testing to analyze the content of manganese ions in different valence states on the sample surface. Figure 6 The XPS spectra show that the discharge products include Mn. 4+ Mn 3+ Mn 2+ This indicates the occurrence of a two-electron transfer reaction in manganese dioxide, in which Mn 2+ The high content indicates that some Mn 4+ Reduced to Mn 2+ The porous conductive carbon generated by the reaction of fluorinated carbon is beneficial for Mn. 2+ The adsorption of Mn can promote the disproportionation reaction and prevent the reaction between lithium metal and Mn. 2+ Side effects.

[0065] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for homogenizing an oil-based slurry of a positive electrode material for a power lithium primary battery, characterized in that: The specific preparation method is as follows: Step 1: Mix electrolytic manganese dioxide, high-power fluorinated carbon, VC, and low aspect ratio VGCF thoroughly; Step 2: Dissolve PVDF in a solvent with a low DN value, and heat and stir until completely dissolved; Step 3: Add the PVDF solution prepared in Step 2 to the powder obtained in Step 1, add a solvent with a low DN value, mix to form a fluid, and obtain the positive electrode slurry; The components are: electrolytic manganese dioxide (50-70 parts by mass), high-power fluorinated carbon (20-40 parts by mass), VC (3-5 parts by mass), low aspect ratio VGCF (2-5 parts by mass), and PVDF (4-5 parts by mass).

2. The oil-based homogenization method for the positive electrode slurry of a power-type lithium primary battery according to claim 1, characterized in that: Low DN value solvents include one or two of triethyl phosphate, trimethyl phosphate, and dimethylformamide.

3. The oil-based homogenization method for the positive electrode slurry of a power lithium primary battery according to claim 2, characterized in that: The F / C ratio of high-power fluorocarbons is less than or equal to 0.

8.

4. The oil-based homogenization method for the positive electrode slurry of a power-type lithium primary battery according to claim 2, characterized in that: The aspect ratio of VGCF is less than or equal to 100.

5. The oil-based homogenization method for the positive electrode slurry of a power lithium primary battery according to claim 2, characterized in that: The specific surface area of ​​VC is greater than 1200m². 2 / g, the molecular weight of PVDF is 350,000-450,000.

6. The oil-based homogenization method for the positive electrode slurry of a power-type lithium primary battery according to any one of claims 1-5, characterized in that: In step one, the mixture is mixed using a ball mill at a speed of 350-450 r / min for 12-20 h. In step three, the slurry is mixed using a ball mill at a speed of 300-500 r / min for 10-12 hours.

7. The oil-based homogenization method for the positive electrode slurry of a power-type lithium primary battery according to claim 6, characterized in that: The homogenization process is carried out in a drying room, with a dew point temperature not exceeding -40℃.

8. A battery positive electrode, characterized in that: The positive electrode slurry is prepared by the oil-based homogenization method for the positive electrode slurry of the power lithium primary battery as described in any one of claims 1-7.

9. A power-type lithium primary battery, characterized in that: It contains the positive electrode of the battery as described in claim 8.

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