Gradient low tortuosity electrode and method of making and battery
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUAZHONG UNIV OF SCI & TECH
- Filing Date
- 2023-05-26
- Publication Date
- 2026-07-21
AI Technical Summary
Existing technologies for preparing thick electrodes for lithium-ion batteries suffer from problems such as electrode cracking, obstructed electron and ion transport, and increased concentration polarization, making it difficult to improve power density and energy density.
The method of preparing a gradient-type low-torsion electrode uses gravity to make the active material and conductive agent distributed in a gradient, and forms channels with gradient distribution that are straight or nearly straight, thus shortening the transport path of lithium ions.
It effectively solves the problem of electrode cracking, improves the utilization rate of active materials, enhances the lithium-ion transport efficiency, improves concentration polarization, and enhances the rate performance of thick electrodes, enabling them to have both high energy density and high power density.
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Figure CN116705977B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of battery technology, specifically to a gradient-type low-torsional-degree electrode, its preparation method, and its application. Background Technology
[0002] In battery systems, the main strategies for improving battery energy density include developing electrode materials with high specific capacity, using high-voltage cathode materials, and increasing electrode thickness. Increasing electrode thickness is more universal than the other two methods and can be applied to most cathode and anode materials and battery systems. However, simply increasing electrode thickness can easily lead to electrode degradation behaviors such as electrode cracking, electrode detachment from the current collector, and polarization.
[0003] Currently, lithium-ion batteries face physical challenges such as electrode cracking during thick electrode fabrication, as well as electrochemical challenges such as poor rate performance and poor cycle stability. The physical challenges primarily stem from the fact that during the thermal drying process, the solvent on the upper layer of the electrode evaporates first, achieving a stable shape initially, while the evaporation of the lower layer of solvent damages the upper layer, leading to electrode cracking. The electrochemical challenges arise because increasing electrode thickness lengthens the electron and ion transport paths, hindering their movement. Furthermore, the lithium-ion transport rate is lower than the electrochemical reaction rate, resulting in increased concentration polarization. This leads to a sacrifice of power density in the pursuit of higher energy density using traditional thick electrodes.
[0004] Therefore, there is an urgent need to develop a thick electrode with significant comprehensive performance advantages and its preparation technology. Summary of the Invention
[0005] Therefore, it is necessary to provide a gradient-type low-torsion electrode, its preparation method, and its application, which can effectively solve the problem of electrode cracking, improve the utilization rate of active materials, efficiently utilize the capacity of electrode active materials, effectively shorten the lithium-ion transport path, improve the concentration polarization problem in traditional thick electrodes, enhance the rate performance of thick electrodes, and enable thick electrodes to have both high energy density and high power density.
[0006] The present invention adopts the following technical solution:
[0007] The present invention provides a gradient-type low-torsion electrode, wherein the electrode active material and conductive agent of the gradient-type low-torsion electrode are generally distributed in a gradient, the electrode has channels with gradient-distributed pore sizes, and some channels are straight or nearly straight, the tortuosity of the channels is 1 to 1.2, preferably 1 to 1.1.
[0008] The present invention also provides a method for preparing the above-mentioned gradient-type low-torsional-degree electrode, comprising the following steps: preparing a slurry containing an active material, a binder, a conductive agent, carbon fiber, and an organic solvent; placing the slurry in a sand core funnel for vacuum filtration, and obtaining a coarse electrode sheet with a gradient distribution of electrode active material and conductive agent based on gravity; placing the coarse electrode in water for phase transformation, and obtaining a low-torsional-degree electrode with a three-gradient distribution of pore size, electrode active material, and conductive agent based on the conversion diffusion between solvent and non-solvent; and drying the low-torsional-degree electrode by drying, rolling, and vacuum drying to obtain the final product.
[0009] In some embodiments, the mass ratio of electrode active material, binder, conductive agent and carbon fiber is (60-99):(1-10):(1-20):(1-10).
[0010] In some embodiments, the mass ratio of electrode active material, binder, conductive agent and carbon fiber is (70-95):(1-10):(3-15):(3-7).
[0011] In some embodiments, the carbon fiber length is 100 nm to 5 μm, preferably 500 nm to 2 μm.
[0012] In some embodiments, the water is deionized water, and the phase transition time is 6 min to 3 h, preferably 0.5 to 2 h.
[0013] In some embodiments, the drying temperature range is 35–80°C, and the drying time is 5–24 hours; preferably, the drying temperature range is 50–60°C, and the drying time is 8–15 hours.
[0014] In some embodiments, the pressure of the roller is 10 to 90 t.
[0015] In some embodiments, the vacuum drying temperature is 70–100°C and the duration is 5–48 h; preferably, the duration is 12–14 h.
[0016] The present invention may also provide a battery comprising the above-described gradient low tortuosity electrode.
[0017] Compared with the prior art, the core advantage of this invention is:
[0018] The present invention provides a method for preparing a gradient-type low-torsion electrode based on gravity. Through steps such as mixing, filtration, phase transformation of the electrode sheet, and rolling, the active material and conductive agent in the electrode sheet can be distributed in a gradient, and channels with vertical or near-vertical (low tortuosity) flow and gradient-distributed pore size can be formed.
[0019] The gradient-type low-torsion electrode of this invention, when applied to a battery system, can effectively solve the problem of electrode cracking, improve the utilization rate of active materials, efficiently utilize the capacity of electrode active materials, effectively shorten the lithium-ion transport path, improve the concentration polarization problem in traditional thick electrodes, enhance the rate performance of thick electrodes, and enable thick electrodes to have both high energy density and high power density. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the process for preparing the gradient-type low-torsional-degree electrode of the present invention.
[0021] Figure 2 This is a schematic diagram of the structure of the three-gradient electrode prepared in Examples 1 and 2.
[0022] Figure 3 The images shown are related monitoring diagrams of the electrode sheet prepared in Example 1; where a and b are morphology diagrams of surface I of the electrode sheet prepared in Example 1 before rolling, d and e are morphology diagrams of surface II of the electrode sheet prepared in Example 1 before rolling, c and f are component concentration ratio diagrams of surface II of the electrode sheet prepared in Example 1 before rolling, g and h are electrode cross-sectional diagrams of the electrode sheet prepared in Example 1 before rolling, and i is a mechanical property test diagram of the electrode sheet prepared in Example 1.
[0023] Figure 4 The cyclic voltammetry curve and cyclic performance diagram are for Example I(a).
[0024] Figure 5 The graph shows a comparison of the rate performance of batteries assembled using electrodes prepared in Examples 1, 2, and 1 (conventional electrodes).
[0025] Figure 6 The graphite electrode prepared using Example 6 is shown in morphology diagram (Figure a) and the cycle performance diagram of the assembled battery is shown in Figure b.
[0026] Figure 7 The image shows the morphology of the silicon electrode prepared using Example 7 (Figure a) and the cycle performance of the assembled battery (Figure b). Detailed Implementation
[0027] like Figure 1 As shown, the technical concept of this invention lies in providing a gradient-type low-torsional-degree electrode based on gravity and its fabrication method, the process flow of which includes:
[0028] S1, Mixing:
[0029] Prepare a slurry containing electrode active material (e.g., LFP), binder (e.g., PVDF), conductive agent (e.g., SP), carbon fiber (CFs), and organic solvent (e.g., NMP).
[0030] S2, filtration:
[0031] The slurry is placed in a sand core funnel for filtration to obtain a coarse electrode sheet with a gradient distribution of active material and conductive agent.
[0032] S3, Water bath reverse phase conversion:
[0033] By placing the coarse electrode in water for water bath reverse phase conversion, a tri-gradient low-torsion electrode with gradient distribution of pore size, active material, and conductive agent is obtained.
[0034] S4. The three-gradient low-torsion electrode is dried at low temperature (not higher than 80°C), rolled, and vacuum dried to obtain a self-supporting gradient electrode with straight channels.
[0035] This invention employs a combination of vacuum filtration and water bath reverse phase conversion to prepare a gradient-type low-torsion gradient electrode. On the one hand, it has the characteristics of gradient distribution of active material, conductive agent and electrode pore size. On the other hand, it has a longitudinally straight or nearly longitudinally straight lithium-ion transport channel with a tortuosity of 1 or close to 1, such as 1 to 1.2, preferably 1 to 1.1, and more preferably 1.
[0036] The preparation method of this invention can be used to prepare both positive and negative electrodes; that is, the electrode active material can be either a positive or negative electrode active material. This method is applicable to the preparation of thick electrodes and can be used in battery systems such as lithium-ion batteries, lithium-sulfur batteries, and lithium metal batteries.
[0037] The present invention will be further described in detail below with reference to specific embodiments, so that those skilled in the art can more clearly understand the present invention. The following embodiments are only used to illustrate the present invention, and are not intended to limit the scope of the present invention. Based on the specific embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention. In the embodiments of the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art; in the embodiments of the present invention, unless specifically specified, the technical means used are conventional means well known to those skilled in the art.
[0038] Example 1
[0039] This embodiment provides a method for preparing an electrode sheet, including the following steps:
[0040] S1, the active material lithium iron phosphate (ball-milled and sieved), the binder polyvinylidene fluoride, the conductive agent SP (carbon black) and the carbon fiber (500nm~2μm) are dispersed evenly in the solvent 1-methyl-2-pyrrolidone in a mass ratio of 80:5:10:5 to obtain a slurry.
[0041] S2, the slurry is introduced into the sand core funnel for filtration to obtain a coarse electrode. The active material and conductive agent in the coarse electrode are distributed in a longitudinal gradient. The side with a high content of active material in the coarse electrode is called the lower side, and the side with a low content of active material in the coarse electrode is called the upper side.
[0042] S3. The coarse electrode is placed in water with its bottom side facing down for phase transformation for 0.5 hours to obtain a tri-gradient electrode intermediate. A portion of the sample is taken and labeled as tri-gradient electrodes I(a) and I(b) for subsequent testing.
[0043] S4. The three-gradient electrode intermediate is placed in an oven and dried at 55°C for 0.5 hours.
[0044] S5, the dried tri-gradient electrode intermediate is then rolled using a roller press with a distance of 100 μm between the two rollers and a pressure of 70 t, denoted as S5. It is then vacuum dried at 85 °C to obtain the final product. SEM samples of the electrode intermediate before and after rolling are prepared, and the morphology of their surface and cross-section is observed.
[0045] Observations revealed that straight channels with gradient apertures were formed, and the electrode tortuosity was 1.1.
[0046] Example 2
[0047] This embodiment provides a method for preparing an electrode sheet, the steps of which are basically the same as those in Embodiment 1, with the only difference being:
[0048] The upper side of the coarse electrode (the side with the lower content of active material in the coarse electrode) was placed face down in water for phase inversion. A portion of the sample was taken and labeled as tri-gradient electrodes II(a) and II(b) for subsequent testing.
[0049] Example 3
[0050] This embodiment provides a method for preparing a thick electrode sheet, the method steps of which are basically the same as those in Embodiment 1, the only difference being that the amount of solid material in the slurry is doubled.
[0051] Example 4
[0052] This embodiment provides a method for preparing an electrode sheet, the steps of which are basically the same as those in Example 1, except that the mass ratio of the active material lithium iron phosphate, the binder polyvinylidene fluoride, the conductive agent and the carbon fiber is 80:3:10:7.
[0053] Example 5
[0054] This embodiment provides a method for preparing an electrode sheet, the steps of which are basically the same as those in Embodiment 1, except that the phase transformation time in water is 1 hour.
[0055] Comparative Example 1
[0056] This comparative example provides a method for preparing a conventional electrode, including the following steps:
[0057] S1, the active material lithium iron phosphate (ball-milled and sieved), the binder polyvinylidene fluoride, and the conductive agent SP are dispersed evenly in the solvent 1-methyl-2-pyrrolidone at a mass ratio of 8:1:1 to obtain a slurry.
[0058] S2, the obtained slurry was uniformly coated onto the current collector using a 1200 μm coater. The electrode was dried in a 60℃ oven for 12 h, and then dried in a vacuum oven at 110℃ for 12 h. Afterwards, the electrode was rolled using a roller press with a distance of 100 μm between the two rollers and a pressure of 70 t. SEM samples were prepared from the electrode intermediates before and after rolling, and the morphology of their surface and cross-sections was observed.
[0059] The electrode sheets prepared in the above experimental example were further punched into circular pieces with a diameter of 8 mm and assembled into batteries in a vacuum glove box. The electrolyte was 1 M LiPF6 dissolved in 1 L of organic solvent (EC:DEC, volume ratio 1:1). The negative electrode was lithium metal.
[0060] The assembled batteries were left to stand for 10 hours to allow the electrolyte to fully soak in. Cyclic voltammetry, impedance testing, rate performance testing, and long-cycle testing were then performed on the assembled batteries.
[0061] The test results are shown in the table below:
[0062]
[0063] In addition, the present invention further studies the preparation and application performance of the negative electrode. The preparation method steps are described in Examples 1 and 2, and some experimental examples are as follows:
[0064] Example 6
[0065] This embodiment provides a method for preparing an electrode sheet, the steps of which are basically the same as those in Embodiment 1, the only difference being that the active material is a graphite anode material.
[0066] Example 7
[0067] This embodiment provides a method for preparing an electrode sheet, the steps of which are basically the same as those in Embodiment 1, the only difference being that the active material is a silicon anode material.
[0068] The morphology and performance of the electrode sheets prepared in the above experimental examples were tested respectively.
[0069] The specific steps for performance testing are as follows: The electrode sheets prepared in the above experimental example are punched into circular pieces with a diameter of 8 mm, and then assembled into batteries in a vacuum glove box. The electrolyte is 1 M LiPF6 dissolved in 1 L of organic solvent (EC:DEC volume ratio 1:1). This is used as the positive electrode, and lithium metal as the negative electrode to assemble a coin cell. The assembled battery is left to stand for 10 hours to allow the electrolyte to fully impregnate it. Long-cycle testing is then performed on the assembled battery.
[0070] The test results of the electrode sheets prepared in Examples 6 and 7 are as follows: Figure 6 and 7 As shown.
[0071] Test results show that the negative electrode sheet obtained by mixing, filtration, and water bath reversal is also a gradient type low tortuosity electrode. The graphite negative electrode prepared in this way can be stably cycled for 500 cycles, and the silicon negative electrode can be stably cycled for 150 cycles.
[0072] It is worth mentioning that the inventors' team discovered through extensive research that:
[0073] 1) Based on the effect of gravity, the present invention uses a combination of vacuum filtration and water bath reverse phase conversion to prepare a gradient electrode with low tortuosity. This allows the active material, conductive agent and electrode pore size to be distributed in a gradient, and forms a lithium-ion transport channel with longitudinal straight or near longitudinal straight, with a tortuosity of 1 or close to 1.
[0074] 2) The preparation method of this invention can be used to prepare both positive and negative electrodes; that is, the electrode active material can be either a positive or negative electrode active material. The method of this invention is applicable to the preparation of thick electrodes and can be used in battery systems such as lithium-ion batteries, lithium-sulfur batteries, and lithium metal batteries.
[0075] It should be noted that the above embodiments are only for further elaboration and explanation of the technical solution of the present invention, and are not intended to further limit the technical solution of the present invention. The method of the present invention is only a preferred embodiment and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for fabricating a gradient-type low-torsivity electrode, characterized in that, Includes the following steps: Prepare a slurry containing electrode active material, binder, conductive agent, carbon fiber and organic solvent; The slurry was placed in a sand core funnel for filtration to obtain coarse electrode sheets in which the electrode active material and conductive agent were distributed in a gradient. The coarse electrode sheet is placed in water to undergo phase transformation, resulting in a low-torsity electrode with a gradient distribution of pore size, electrode active material, and conductive agent. The low-torsivity electrode is dried and rolled to obtain a gradient-type low-torsivity electrode sheet. The electrode active material and the conductive agent are generally distributed in a gradient, and the gradient-type low-torsion electrode sheet has straight or semi-straight channels with gradient-distributed pore sizes, and the tortuosity of the channels is 1~1.
2.
2. The method for preparing a gradient-type low-torsion electrode according to claim 1, characterized in that, The mass ratio of electrode active material, binder, conductive agent and carbon fiber is (60~99):(1~10):(1-20):(1~10).
3. The method for preparing a gradient-type low-torsivity electrode according to claim 2, characterized in that, The mass ratio of electrode active material, binder, conductive agent and carbon fiber is (70~95):(1~10):(3-15):(3~7).
4. The method for preparing a gradient-type low-torsivity electrode according to claim 1, characterized in that, The carbon fiber has a length of 100 nm to 5 μm.
5. The method for preparing a gradient-type low-torsivity electrode according to any one of claims 1 to 4, characterized in that, The water is deionized water, and the phase transition time is 6 min to 3 h.
6. The method for preparing a gradient-type low-torsivity electrode according to claim 5, characterized in that, The drying temperature range is 35~80 ℃, and the duration is 5~24h.
7. The method for preparing a gradient-type low-torsivity electrode according to claim 5, characterized in that, The pressure of the roller is 10~90t.
8. The method for preparing a gradient-type low-torsivity electrode according to claim 5, characterized in that, It also includes a step of vacuum drying the rolled electrode sheet, wherein the vacuum drying temperature is 70~100℃ and the duration is 5~48 h.
9. A battery, characterized in that, The invention comprises a gradient-type low-torsional-degree electrode prepared by the preparation method according to any one of claims 1 to 8.