A non-hysteresis high specific energy lithium-calcium fluoride electrode and a method for preparing the same

Abstract

The application discloses a kind of no hysteresis high specific energy lithium fluorocarbon electrode and preparation method thereof, the preparation method includes the following steps: step 1, take first carbon material, second carbon material, the specific surface area of first carbon material is greater than second carbon material;First carbon material and second carbon material are fluorinated simultaneously using gas phase fluorination method, obtain the composite fluorocarbon material containing high fluorocarbon ratio fluorocarbon and low fluorocarbon ratio fluorocarbon;Step 2, conductive agent, binder and the composite fluorocarbon material obtained in step 1 are dispersed in solvent to form slurry, coated on current collector, and the composite fluorocarbon electrode is obtained after drying.The application simultaneously fluorinates first carbon material (large specific surface area carbon material) and second carbon material (small specific surface area carbon material), and the composite fluorocarbon material containing two fluorocarbon ratios (high fluorocarbon ratio and low fluorocarbon ratio) is prepared.

Description

Technical Field

[0001] This invention relates to the field of lithium primary battery technology, specifically to a hysteresis-free high-energy-density lithium fluoride carbon electrode and its preparation method. Background Technology

[0002] Lithium fluoride carbon batteries are a type of high-energy-density lithium battery. They have high stability, high safety, and excellent storage performance, and can meet the high-level intelligent energy needs. They can be applied in fields such as marine floats, pacemakers, and capsule endoscopes.

[0003] Fluorinated carbon materials are classified into high fluorine-to-carbon ratio (FCR) and low FCR materials. Higher fluorine content results in higher battery specific energy; therefore, most existing lithium-ion fluorinated carbon batteries use high FCR materials as the positive electrode. However, higher fluorine content in fluorinated carbon leads to poorer intrinsic conductivity. Consequently, high FCR fluorinated carbon materials exhibit poor conductivity and slow electrode kinetics, resulting in voltage lag in the initial discharge phase during practical applications, thus affecting battery discharge performance.

[0004] Currently, the method to improve the voltage hysteresis in the early stage of discharge of lithium fluorocarbon batteries is to dope metal oxides into materials with a high fluorine-to-carbon ratio. However, the specific energy of metal oxides is relatively small, which leads to a decrease in the overall specific energy of the battery.

[0005] Therefore, there is an urgent need to develop a fluorinated carbon electrode with high specific energy and no voltage hysteresis in the early stage of battery discharge. Summary of the Invention

[0006] The purpose of this invention is to provide a fluorinated carbon electrode with high specific energy and no voltage hysteresis.

[0007] To achieve the above objectives, the present invention provides a method for preparing a composite fluorinated carbon electrode, the method comprising the following steps:

[0008] Step 1: Take a first carbon material and a second carbon material, wherein the specific surface area of ​​the first carbon material is greater than that of the second carbon material; use a gas-phase fluorination method to simultaneously fluorinate the first carbon material and the second carbon material to obtain a composite fluorinated carbon material containing high fluorine-to-carbon ratio fluorinated carbon and low fluorine-to-carbon ratio fluorinated carbon.

[0009] Step 2: Disperse the conductive agent, binder, and composite fluorinated carbon material obtained in Step 1 in a solvent to form a slurry, coat it on the current collector, and dry it to obtain the composite fluorinated carbon electrode.

[0010] Optionally, the first carbon material is porous carbon with a primary particle size of 15–30 μm; the second carbon material is multi-walled carbon nanotubes with a diameter of 10–20 nm.

[0011] Optionally, in step 1, the fluorination reaction temperature is 350–500°C, and the fluorination reaction time is 4–8 hours.

[0012] Optionally, the carbon ratio of the high fluorocarbon ratio fluorinated carbon is 1.05 to 1.10, and the carbon ratio of the low fluorocarbon ratio fluorinated carbon is 0.85 to 0.90.

[0013] Optionally, in step 2, the mass ratio of solvent, binder, conductive agent, and composite fluorocarbon material is (2-3):(0.05-0.1):(0.02-0.08):(0.85-0.9).

[0014] Optionally, the conductive agent includes spherical conductive agents and linear conductive agents, wherein the spherical conductive agent has a primary particle size of 1-100 nm, and the linear conductive agent has a diameter of 10-500 nm.

[0015] Optionally, the spherical conductive agent includes Super P, and the linear conductive agent includes CNT and / or VGCF.

[0016] Optionally, when the adhesive is polyvinylidene fluoride, the solvent is N-methylpyrrolidone.

[0017] Optionally, when the adhesive is LA133, the solvent is an aqueous solution of ethanol or an aqueous solution of isopropanol.

[0018] The present invention also provides a hysteresis-free high-energy-density lithium fluorinated carbon electrode prepared by the above preparation method. The electrode uses a composite fluorinated carbon material containing low-fluorine-carbon-ratio fluorinated carbon and high-fluorine-carbon-ratio fluorinated carbon as the active material. Since the conductivity of low-fluorine-carbon-ratio fluorinated carbon is higher than that of high-fluorine-carbon-ratio material, the discharge is mainly carried out by low-fluorine-carbon-ratio material in the early stage of battery discharge, which solves the problem of voltage hysteresis in the early stage of high-fluorine-carbon-ratio fluorinated carbon battery discharge, effectively improves battery discharge performance, enhances battery low-temperature adaptability, and expands the application range of lithium fluorinated carbon battery.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The present invention fluorinates a first carbon material (a carbon material with a large specific surface area) and a second carbon material (a carbon material with a small specific surface area) simultaneously. Under the same reaction conditions, the first carbon material with a large specific surface area reacts with more fluorinated gas to form a high fluorine-to-carbon ratio fluorinated carbon, and the second carbon material with a small specific surface area reacts with less fluorinated gas to form a low fluorine-to-carbon ratio fluorinated carbon, thereby simultaneously producing a composite fluorinated carbon material containing two fluorine-to-carbon ratios (high fluorine-to-carbon ratio and low fluorine-to-carbon ratio).

[0021] Furthermore, this invention uses the composite fluorinated carbon material as the electrode active material. Since the conductivity of low fluorine-carbon ratio fluorinated carbon is higher than that of high fluorine-carbon ratio material, the low fluorine-carbon ratio material is mainly used for discharge in the early stage of battery discharge, which solves the problem of voltage lag in the early stage of discharge of high fluorine-carbon ratio fluorinated carbon battery and effectively improves battery discharge performance.

[0022] (2) The present invention mixes the first carbon material and the second carbon material and then fluorinates them simultaneously. Compared with fluorinating the two materials separately and then mixing them, the two materials can agglomerate more evenly, improve the contact between the two materials and the consistency of their state during discharge, and effectively improve the battery discharge performance.

[0023] (3) Compared with existing doped metal oxides, the present invention incorporates low fluorine-to-carbon ratio fluorinated carbon materials into high fluorine-to-carbon ratio fluorinated carbon materials, thereby solving the problem of large voltage lag in the early stage of battery discharge without reducing the specific energy of the fluorinated carbon materials.

[0024] Furthermore, low-fluorine carbon batteries, compared to fluorinated carbon batteries, will form carbon after the initial discharge of the battery. This carbon will then act as a conductive agent, further improving the overall conductivity of the electrode, thereby enhancing the battery's adaptability at low temperatures and expanding the application range of lithium fluorinated carbon batteries.

[0025] (4) This invention uses two types of conductive agents, spherical and linear, to construct a three-dimensional conductive network. Compared to using spherical conductive agents alone, linear conductive agents can connect adjacent spherical conductive agents, improving the contact between the conductive agent and the fluorinated carbon material, thereby improving the overall conductivity of the battery. Compared to the two-dimensional conductive network formed by using linear conductive agents alone, the addition of spherical conductive agents forms a well-developed three-dimensional conductive network, thereby improving the overall conductivity of the battery. Attached Figure Description

[0026] Figure 1 The graph shows a comparison of the discharge curves of the lithium fluoride carbon battery prepared in Example 1 and the lithium fluoride carbon battery in Comparative Example 1 at 0.05C room temperature.

[0027] Figure 2 The graph shows a comparison of the discharge curves of the lithium fluoride carbon battery prepared in Example 2 and the lithium fluoride carbon battery in Comparative Example 2 at 0°C and 0.05C.

[0028] Figure 3 A comparison of the discharge curves of the lithium fluoride carbon battery prepared in Example 6 and the lithium fluoride carbon battery in Comparative Example 6 at -20°C and 0.05C. Detailed Implementation

[0029] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0030] This invention provides a method for preparing a composite fluorinated carbon electrode, the method comprising the following steps:

[0031] Step 1: Take a first carbon material and a second carbon material, wherein the specific surface area of ​​the first carbon material is greater than that of the second carbon material; use a gas-phase fluorination method to simultaneously fluorinate the first carbon material and the second carbon material. Since the specific surface area of ​​the first carbon material is greater than that of the second carbon material, during simultaneous fluorination, the first carbon material reacts with more fluorinated gas to generate high fluorine-to-carbon ratio fluorinated carbon, while the second carbon material reacts with less fluorinated gas to generate low fluorine-to-carbon ratio fluorinated carbon. Thus, this invention obtains a composite fluorinated carbon material that simultaneously contains both high fluorine-to-carbon ratio fluorinated carbon and low fluorine-to-carbon ratio fluorinated carbon.

[0032] Furthermore, this invention involves simultaneously fluorinating a mixture of the first carbon material and the second carbon material. Compared to fluorinating the two materials separately and then mixing them, the fluorination process causes the two materials to agglomerate into blocks, improving the contact between the two materials and effectively improving the battery discharge performance.

[0033] In some embodiments, the first carbon material is porous carbon with a primary particle size of 15–30 μm; the second carbon material is multi-walled carbon nanotubes with a diameter of 10–20 nm.

[0034] The particle size of the multi-walled carbon nanotubes is smaller than that of porous carbon. Therefore, during the fluorination process, the multi-walled carbon nanotubes can fill the gaps formed by adjacent porous carbon, which further improves the contact between the two materials and improves the battery discharge performance.

[0035] In some embodiments, the fluorinated gas can be one of a mixture of nitrogen and fluorine or a mixture of nitrogen and nitrogen trifluoride, wherein the volume fraction percentage of nitrogen and fluorine or nitrogen trifluoride is 20-40:60-80.

[0036] In some embodiments, the fluorination reaction temperature is 350–500°C, and the reaction time is 4–8 hours. By adjusting the fluorination reaction conditions, the degree of fluorination of the first carbon material and the second carbon material of the present invention can be adjusted to obtain high fluorine-to-carbon ratio fluorinated carbon and low fluorine-to-carbon ratio fluorinated carbon with ideal fluorine-to-carbon ratio.

[0037] In some embodiments, the fluorine-to-carbon ratio of high fluorine-to-carbon fluoride is 1.05 to 1.10, and the fluorine-to-carbon ratio of low fluorine-to-carbon fluoride is 0.85 to 0.90.

[0038] Step 2: Disperse the conductive agent, binder, and composite fluorinated carbon material obtained in Step 1 in a solvent to form a slurry, coat it on the current collector, and dry it to obtain the composite fluorinated carbon electrode.

[0039] In some embodiments, the conductive agent comprises two dimensions: spherical and linear conductive agents. Compared to single-dimensional conductive agents, this invention constructs a more developed three-dimensional conductive network using two-dimensional conductive agents, improving the contact between the conductive agent and the fluorinated carbon material, and enhancing the overall conductivity of the battery.

[0040] In some embodiments, the adhesive includes polyvinylidene fluoride and / or LA133, which can bond the conductive agent and the composite fluorocarbon material together, and are chemically inert within the potential range of battery charging and discharging, and will not react with the electrolyte or lithium.

[0041] In some embodiments, the conductive agent includes two-dimensional conductive agents: Super P (spherical conductive agent), CNT and / or VGCF (linear conductive agent). The use of two-dimensional conductive agents constructs a three-dimensional conductive network with better conductivity, improves the contact between the conductive agent and the fluorinated carbon material, and improves the overall conductivity of the battery.

[0042] In some embodiments, the adhesive includes polyvinylidene fluoride and / or LA133, which can bond the conductive agent and the composite fluorocarbon material and remain stable within the potential range of battery charging and discharging without reacting with the electrolyte or other electrode materials.

[0043] When the adhesive is polyvinylidene fluoride, N-methylpyrrolidone, an oil-based solvent, is used as the solvent to disperse the conductive agent, adhesive, and composite fluorocarbon material.

[0044] When the adhesive is LA133, the conductive agent, adhesive, and composite fluorocarbon material are dispersed using an aqueous solvent such as ethanol aqueous solution or isopropanol aqueous solution.

[0045] In some embodiments, the alcohol content in the aqueous solvent is 10-20 wt.% and the water content is 80-90 wt.%.

[0046] The present invention also provides a hysteresis-free high-energy-density lithium fluorinated carbon electrode prepared by the above preparation method. The electrode uses a composite fluorinated carbon material containing low-fluorine-carbon-ratio fluorinated carbon and high-fluorine-carbon-ratio fluorinated carbon as the active material. Since the conductivity of low-fluorine-carbon-ratio fluorinated carbon is higher than that of high-fluorine-carbon-ratio material, the discharge is mainly carried out by low-fluorine-carbon-ratio material in the early stage of battery discharge, which solves the problem of voltage hysteresis in the early stage of high-fluorine-carbon-ratio fluorinated carbon battery discharge, effectively improves battery discharge performance, enhances battery low-temperature adaptability, and expands the application range of lithium fluorinated carbon battery.

[0047] The present invention also provides a hysteresis-free high-energy-density lithium fluoride carbon battery, which uses the above-mentioned composite fluoride carbon electrode as the positive electrode and lithium metal or lithium alloy as the negative electrode, and there is no voltage hysteresis phenomenon in the early stage of battery discharge.

[0048] The following description is based on specific embodiments.

[0049] Example 1

[0050] This embodiment provides a method for preparing a composite fluorinated carbon electrode, including:

[0051] Step 1, Preparation of composite fluorinated carbon materials:

[0052] Step 1.1: Porous carbon and multi-walled carbon nanotubes are placed in a nickel crucible of a fluorination device at a mass ratio of 9:1. Then, a nitrogen-fluorine mixture with a volume fraction of 30:70 is introduced. The fluorination reaction is then carried out under heating conditions of 400℃. After 6 hours of reaction, a composite fluorinated carbon material is obtained.

[0053] Step 1.2: Place the above-mentioned composite fluorocarbon material into a high-energy ball mill and ball mill it at a speed of 800-1200 rpm for 30-60 minutes. Then pass it through a 500-800 mesh sieve to obtain the composite fluorocarbon material.

[0054] The primary particle size of the aforementioned fluorinated porous carbon is 15–30 μm, while the diameter of the multi-walled carbon nanotubes is 10–20 nm. Because the specific surface area of ​​porous carbon is greater than that of multi-walled carbon nanotubes, when both are fluorinated simultaneously under the same conditions, the porous carbon reacts with more fluorinated gases, resulting in a higher degree of fluorination.

[0055] Step 2, Preparation of composite fluorinated carbon positive electrode sheet:

[0056] Step 2.1: Add the binder polyvinylidene fluoride, conductive agent Super P, conductive agent CNT, and composite fluorinated carbon to the solvent N-methylpyrrolidone in a mass ratio of 0.06:0.03:0.01:0.9 and disperse and stir to obtain the positive electrode slurry.

[0057] Step 2.2: After ball milling the above-mentioned positive electrode slurry through a 50-mesh sieve, the positive electrode slurry is coated onto carbon-coated aluminum foil using a coating machine, with a coating density of 8–12 mg / cm³. 2 The coated electrode sheets were dried in an 80°C forced-air oven for 2 hours, and then dried in a 90°C vacuum oven for 24 hours.

[0058] Step 2.3: Roll and punch the dried electrode sheet to obtain composite fluorinated carbon positive electrode sheet.

[0059] Step 3, Preparation of high-energy-density lithium-carbon fluoride batteries without hysteresis:

[0060] The composite fluorinated carbon positive electrode, separator, and lithium metal negative electrode are sequentially stacked into the stainless steel shell of the coin cell, and 30 μL of lithium primary electrolyte is added between each layer. The coin cell is then assembled in a glove box.

[0061] Comparative Example 1

[0062] The difference between this embodiment and Embodiment 1 is that in step 1, all fluorinated carbon materials are prepared using porous carbon, and all the obtained fluorinated carbon materials are high fluorine-to-carbon ratio fluorinated carbon materials.

[0063] like Figure 1 The figure shows a comparison of the discharge curves of the lithium fluoride carbon battery prepared in Example 1 and the lithium fluoride carbon battery in Comparative Example 1 at 0.05C room temperature. It can be seen from the figure that the voltage hysteresis in the initial discharge phase of the battery in Example 1 was completely eliminated, and the discharge specific energy was not affected.

[0064] Example 2

[0065] The difference between this embodiment and Embodiment 1 is that in step 1, the mass ratio of porous carbon to multi-walled carbon nanotubes is 8:2.

[0066] Comparative Example 2

[0067] The difference between this embodiment and embodiment 2 is that in step 1, all fluorinated carbon materials are prepared using porous carbon, and all the obtained fluorinated carbon materials are high fluorine-to-carbon ratio fluorinated carbon materials.

[0068] like Figure 2 The figure shows a comparison of the discharge curves of the lithium fluoride carbon battery prepared in Example 2 and the lithium fluoride carbon battery in Comparative Example 2 at 0°C and 0.05C. It can be seen from the figure that the lithium fluoride carbon battery of Example 2 has no significant voltage hysteresis in the initial stage of discharge and has no significant impact on the discharge specific energy.

[0069] Example 3

[0070] The difference between this embodiment and Embodiment 1 is that in step 1, the mass ratio of porous carbon to multi-walled carbon nanotubes is 7:3, the fluorination temperature is 450℃, and the fluorination time is 5 hours.

[0071] Example 4

[0072] The difference between this embodiment and embodiment 1 is that in step 2, the conductive agents are Super P and VGCF.

[0073] Example 5

[0074] The difference between this embodiment and Embodiment 1 is that in step 3, 40 μL of lithium primary electrolyte is added between the composite fluorinated carbon positive electrode, the separator, and the lithium metal negative electrode.

[0075] Example 6

[0076] The difference between this embodiment and Embodiment 1 is that in step 2, the binder is LA133 and the solvent is a 10wt.% aqueous ethanol solution.

[0077] Comparative Example 6

[0078] The difference between this embodiment and embodiment 6 is that in step 1, all fluorinated carbon materials are prepared using porous carbon, and all the obtained fluorinated carbon materials are high fluorine-to-carbon ratio fluorinated carbon materials.

[0079] like Figure 3 The figure shows a comparison of the discharge curves of the lithium fluorinated carbon battery prepared in Example 6 and the lithium fluorinated carbon battery in Comparative Example 6 at -20°C and 0.05C. It can be seen from the figure that the initial voltage hysteresis of the lithium fluorinated carbon battery in Example 6 is significantly less than that in Comparative Example 6, and it also exhibits a higher voltage plateau. Furthermore, the discharge curves show that due to the difference in intrinsic conductivity of the composite materials, the lithium fluorinated carbon battery in Example 6 exhibits two discharge plateaus. Initially, the discharge is dominated by the low-fluorine-to-carbon ratio fluorinated carbon material. Subsequently, the low-fluorine-to-carbon ratio fluorinated carbon discharges and generates carbon, which acts as a conductive agent to provide heat for the subsequent discharge of the high-energy-density fluorinated carbon material. This reduces voltage hysteresis and contributes to the overall performance of the battery.

[0080] In summary, this invention incorporates low-fluorine-to-carbon ratio fluorinated carbon materials into high-fluorine-to-carbon ratio fluorinated carbon materials. In the initial stage of battery discharge, the battery primarily discharges through the low-fluorine-to-carbon ratio material. Utilizing the high conductivity and rapid electrode kinetics of the low-fluorine-to-carbon ratio material, the problem of voltage lag in the initial stage of battery discharge is eliminated, effectively improving battery discharge performance, enhancing battery low-temperature adaptability, and expanding the application range of lithium fluorinated carbon batteries.

[0081] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for preparing a composite carbon fluoride electrode, characterized by, The method comprises the following steps: Step 1, taking a first carbon material and a second carbon material, the specific surface area of the first carbon material being greater than that of the second carbon material; simultaneously fluorinating the first carbon material and the second carbon material by a gas-phase fluorination method to obtain a composite fluorocarbon material containing high-fluorocarbon-ratio fluorocarbon and low-fluorocarbon-ratio fluorocarbon; the first carbon material is porous carbon with a primary particle size of 15-30 μm; the second carbon material is multi-walled carbon nanotube with a diameter of 10-20 nm; the high-fluorocarbon-ratio fluorocarbon has a fluorocarbon ratio of 1.05-1.10, and the low-fluorocarbon-ratio fluorocarbon has a fluorocarbon ratio of 0.85-0.90; the fluorination reaction has a reaction temperature of 350-500 ℃ and a reaction time of 4-8 hours; Step 2, dispersing a conductive agent, a binder, and the composite fluorocarbon material obtained in Step 1 in a solvent to form a slurry, coating the slurry on a current collector, and drying to obtain the composite fluorocarbon electrode.

2. The method for preparing the composite fluorinated carbon electrode as described in claim 1, characterized in that, In Step 2, the mass ratio of the solvent, the binder, the conductive agent, and the composite fluorocarbon material is (2-3):(0.05-0.1):(0.02-0.08):(0.85-0.9).

3. The method for preparing the composite fluorinated carbon electrode as described in claim 1, characterized in that, The conductive agent comprises a spherical conductive agent and a linear conductive agent, the spherical conductive agent having a primary particle size of 1-100 nm, and the linear conductive agent having a diameter of 10-500 nm.

4. The method for preparing the composite fluorinated carbon electrode as described in claim 3, characterized in that, The spherical conductive agent comprises Super P, and the linear conductive agent comprises CNT and / or VGCF.

5. The method for preparing the composite fluorinated carbon electrode as described in claim 1, characterized in that, When the binder is polyvinylidene fluoride, the solvent is N-methylpyrrolidone.

6. The method for preparing the composite fluorinated carbon electrode as described in claim 1, characterized in that, When the binder is LA133, the solvent is an ethanol aqueous solution or an isopropyl alcohol aqueous solution.

7. A composite carbon fluoride electrode, characterized by, The composite fluorocarbon electrode is prepared by the preparation method of the composite fluorocarbon electrode according to any one of claims 1-6.

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