Lithium ion battery negative pole piece and preparation method thereof

Abstract

The invention relates to a lithium ion battery negative pole piece and a preparation method thereof. The pole piece takes an intermediate polymer base material as a core, the two sides of the intermediate polymer base material are coated with conducting layers with the thickness of 5-20 nm, the conducting layers are formed by blade coating, spin coating or dip coating of a specific conducting glue solution, and in the formula of the conducting glue solution, polyvinylpyrrolidone accounts for 10%-30%, carbon nanotubes account for 5%-10%, metal nanowires account for 1%-5%, ethyl alcohol accounts for 50%-80%, and tetraethylammonium tetrafluoroborate accounts for 1%-2%. In addition, a porous material layer is arranged on the outer side of the conducting layer. The preparation method of the negative pole piece comprises the following steps: pretreating the surface of an intermediate polymer substrate, preparing a conductive adhesive solution, coating two sides of the substrate with the conductive adhesive solution, and drying to form a conductive layer; and compounding the porous material layer with the base material with the conductive layer to prepare the integrated composite electrode plate. According to the novel current collector structure, traditional copper foil is replaced by the intermediate polymer base material, the weight is remarkably reduced, the energy density of the battery is improved, meanwhile, the specific conductive glue solution enables the microstructure of the conductive layer to be more uniform, the interface impedance is reduced, the lithium dendrite growth risk is reduced, and the safety of the battery is greatly improved.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a negative electrode plate for a lithium-ion battery. Background Art

[0002] In the lithium-ion battery technology system, electrode materials, separators and electrolytes together constitute the core elements of battery performance. The current collector is a key component of the electrode structure. Its material selection and functional design directly affect the battery's energy density, cycle life and safety. The current mainstream lithium-ion battery uses aluminum foil as the positive electrode current collector and copper foil as the negative electrode current collector. This configuration stems from the difference in the characteristics of the two metal materials and the adaptation requirements of the battery's electrochemical mechanism.

[0003] Among them, the core functions of copper foil as a negative electrode current collector are mainly reflected in three aspects: First, with its excellent conductive properties (conductivity can reach 5.8×10 7 S / m) realizes efficient transmission of electrons between the negative electrode active material and the external circuit, significantly improving the charge and discharge energy efficiency by reducing the internal resistance of the battery; secondly, the surface resistance distribution of the copper foil is guaranteed to be uniform through the precisely controlled microstructure, thereby ensuring the uniform diffusion of current between the negative electrode material layers, effectively suppressing the risk of local thermal runaway; thirdly, relying on the mechanical strength of the copper foil (tensile strength ≥ 200MPa), it provides structural support for silicon-based / graphite and other negative electrode materials, maintains the stability of the electrode morphology during the lithium ion insertion / extraction process, and prevents capacity decay caused by the peeling of active materials. This multifunctional synergistic mechanism makes copper foil one of the key materials supporting the stable operation of high-energy-density lithium-ion batteries.

[0004] However, the traditional copper foil current collector still has shortcomings, which limits the further improvement of battery performance. The weight and thickness of copper foil form a natural shackle on the battery energy density. Its unit area mass is relatively large (for example, the surface density of 6μm copper foil is about 5.06mg / cm 2 ), which becomes a burden in the pursuit of high-energy-density batteries, making it difficult for the overall energy density of batteries to break through the existing bottleneck; Secondly, the rigidity of copper foil is fundamentally inconsistent with the development needs of flexible batteries. Traditional copper foil is prone to cracking or even breaking during bending (the bending radius usually needs to be greater than 3mm), which cannot meet the stringent battery flexibility requirements in wearable devices, foldable screen mobile phones and other fields. Furthermore, it is difficult to control the uniformity of the copper foil surface microstructure, and local stress concentration points are easily generated during the production process. These defects not only increase the interface impedance (the measured interface resistance fluctuation can reach ±15%), but may also become the starting point for lithium dendrite growth, inducing the risk of battery short circuit. Summary of the Invention

[0005] In order to solve the above-mentioned technical problems, the present application provides a lithium-ion battery negative electrode plate and a preparation method thereof, aiming to break through the performance limitations of traditional copper foil through a new current collector structure design.

[0006] In the first aspect, the present application provides a lithium-ion battery negative electrode plate adopting the following technical solution: A lithium-ion battery negative electrode plate, comprising: a middle polymeric substrate having two opposing sides; A conductive layer is provided on both sides of the intermediate polymer substrate, and the thickness of the conductive layer is 5-20 nm; The porous material layer is disposed on a side of the conductive layer away from the intermediate polymer substrate; The conductive layer is formed by coating a conductive adhesive on both sides of the intermediate polymer substrate by blade coating, spin coating or dip coating. The raw materials for preparing the conductive adhesive include the following components in terms of weight percentage: Polyvinyl pyrrolidone 10%-30%, carbon nanotubes 5%-10%, metal nanowires 1%-5%, ethanol 50%-80%, and tetraethylammonium tetrafluoroborate 1-2%.

[0007] By adopting the above technical solution, the traditional copper foil affects the battery energy density due to its weight and thickness. The negative electrode plate adopts a structure with conductive layers on both sides of the intermediate polymer substrate and then a porous material layer. This is expected to reduce the weight of the current collector itself, thereby improving the overall energy density of the battery and breaking through the existing bottleneck. In addition, in flexible batteries, the separator with a conductive layer can be used as part of the current collector, simplifying the battery structure. In addition, the conductive layer of the negative electrode plate is formed by coating with a specific conductive glue. The raw materials for its preparation include polyvinyl pyrrolidone, carbon nanotubes, metal nanowires and other ingredients, which make the surface microstructure of the conductive layer more uniform, reduce the interface impedance and the risk of lithium dendrite growth, thereby improving battery safety.

[0008] Furthermore, the specific preparation method of the conductive layer is as follows: 1) Preparation of a conductive adhesive: Carbon nanotubes and metal nanowires are added to ethanol and ultrasonically dispersed to form a dispersion. Polyvinyl pyrrolidone is then added to the dispersion and stirred in a water bath until completely dissolved. Tetraethylammonium tetrafluoroborate is then added, stirring is continued, and finally vacuum degassing is performed to obtain a conductive adhesive. 2) Coating of conductive adhesive: First, surface treatment is performed on both sides of the intermediate polymer substrate, and then the intermediate polymer substrate is fixed on the rotary disk of the spin coater. The conductive adhesive is evenly spin-coated onto the intermediate polymer substrate at a certain rate, and a conductive layer is formed after drying.

[0009] By adopting the above technical solutions, the conductive material is evenly dispersed, the thickness and uniformity of the conductive layer are precisely controlled, and the bonding strength between the conductive layer and the substrate is improved, thereby enhancing the electron transmission efficiency, reducing the internal resistance, suppressing thermal runaway, maintaining electrode stability, and comprehensively improving battery performance.

[0010] Optionally, the substrate of the porous material layer is selected from any one of porous ceramics, metal foam, and MXene.

[0011] Optionally, the intermediate polymer substrate is made of at least one of polypropylene and polyethylene.

[0012] In a second aspect, the present application provides a method for preparing a negative electrode sheet for a lithium-ion battery using the following technical solution: A method for preparing a negative electrode sheet for a lithium ion battery comprises the following steps: S1. Pre-treating the surface of the intermediate polymer substrate, then preparing a conductive adhesive, coating the conductive adhesive on both sides of the intermediate polymer substrate, and drying to obtain a conductive layer; S2. Compounding the porous material layer with the intermediate polymer substrate with the conductive layer to obtain an integrated composite electrode plate.

[0013] By adopting the following technical solutions, the preparation method enhances interface bonding, optimizes electrode structure, improves lithium ion transmission and electron conduction efficiency, and thus improves battery performance through substrate pretreatment, conductive layer coating and porous material composite.

[0014] In summary, this application has the following beneficial effects: 1. In terms of structural design and performance improvement, this application innovatively adopts a new current collector structure with conductive layers and porous material layers on both sides of an intermediate polymer substrate (diaphragm). This design breaks through the limitations of traditional copper foil, effectively reducing the weight of the current collector and thereby improving the energy density of the battery. At the same time, the application of a specific conductive adhesive makes the microstructure of the conductive layer more uniform, which not only reduces the interfacial impedance but also reduces the risk of lithium dendrite growth, thereby significantly improving the safety of the battery. 2. In terms of preparation process and cost control, the preparation method of the present application is simple and easy to implement through the steps of substrate pretreatment, conductive layer coating and porous material composite. This preparation method not only optimizes the overall structure of the electrode, improves the efficiency of lithium ion transmission and electron conduction, but also improves production efficiency. In addition, the design of replacing copper foil with a diaphragm reduces the use of copper foil, thereby reducing material costs and further improving the economy and practicality of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the structure of the negative electrode plate of the lithium-ion battery in this application. DETAILED DESCRIPTION

[0016] To more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. It should be understood that the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0017] The purpose of the present invention is illustrated by the following examples. The components of the composition are illustrated in parts by weight as a general standard. Unless otherwise specified, for the sake of simplicity, the "parts" described in the examples of the present invention have the same meaning as parts by weight.

[0018] Unless otherwise specified, all reagents and instruments used were commercially available.

[0019] Performance testing The lithium-ion battery negative electrode sheets prepared in each embodiment or comparative example were cut into discs with a diameter of 10 mm as the negative electrode, and then the lithium sheet was used as the counter electrode and 1M LiPF6 (EC:DMC=1:1) was used as the electrolyte to assemble and package the battery.

[0020] (1) Electrochemical performance 1. Initial charge and discharge efficiency Charge and discharge at a constant current rate of 0.1C, with a voltage range of 0.01-2.0V. Record the initial charge and discharge capacity and calculate the efficiency. The calculation formula is as follows: 2. Rate performance test Charge and discharge at a 5C rate, record the capacity retention rate, and calculate it using the following formula: 3. Cycle life test The battery was cycled 1000 times at a rate of 1C and the capacity decay ratio was recorded.

[0021] (2) Interface stability The internal resistance of the battery was tested using an electrochemical workstation impedance spectroscopy (EIS) with a frequency range of 10 MHz to 100 kHz, and the stability of the interface film was determined in combination with the DCR test.

[0022] All batteries in the above tests were assembled in the same batch, and the test environment temperature was 25±1℃.

[0023] Example 1 A lithium-ion battery negative electrode plate, see attached Figure 1 The basic structure thereof is, from top to bottom, a porous ceramic layer, a conductive layer, a PP-PE composite diaphragm, a conductive layer, and a porous ceramic layer, and is prepared by the following method: S1. Add 5 g of carbon nanotubes and 2 g of metal nanowires to 50 g of ethanol, and ultrasonically disperse them at 20 kHz at 20°C for 30 minutes to form a uniform dispersion. Then, add 20 g of polyvinyl pyrrolidone to the dispersion, stir in a 60°C water bath for 2 hours until completely dissolved, then add 1 g of tetraethylammonium tetrafluoroborate, continue stirring for 30 minutes, and then place in a vacuum degassing machine to eliminate bubbles to obtain a conductive adhesive, wherein the metal matrix of the metal nanowires is Cu; S2. The surface of the PP-PE composite membrane was cleaned with ethanol, dried with nitrogen, and placed on the rotary disk of a spin coater. The conductive adhesive was evenly spin-coated on the PP-PE composite membrane at a speed of 2000 rpm to form a conductive layer. The thickness of the conductive layer was measured using a step profiler to ensure that it was within the range of 5-20 nm. After natural drying, the PP-PE composite membrane with a conductive layer was obtained. S3. The porous alumina slurry is evenly coated on the outside of the conductive layer formed above by a doctor blade method, with a thickness controlled at 50 μm. After drying at 80°C for 2 hours, a porous material layer with a pore size of 75 nm is formed. Finally, the electrode is placed in a tablet press and pressed at a pressure of 0.3 MPa for 5 minutes to obtain an integrated structure of the lithium-ion battery negative electrode.

[0024] Example 2 A negative electrode plate for a lithium-ion battery, the only difference from Example 1 is that its basic structure from top to bottom is a porous ceramic layer, a conductive layer, a PP separator, a conductive layer, and a porous ceramic layer.

[0025] Example 3 A negative electrode plate for a lithium-ion battery, the only difference from Example 1 being that its basic structure from top to bottom is foamed metal nickel, a conductive layer, a PP-PE composite separator, a conductive layer, and foamed metal nickel.

[0026] Example 4 A lithium-ion battery negative electrode plate, the only difference from Example 1 is that its basic structure from top to bottom is MXene, conductive layer, PP-PE composite separator, conductive layer, MXene.

[0027] Examples 5-10 A lithium-ion battery negative electrode plate, the only difference from Example 1 is that the amount (g) of each component in the conductive adhesive preparation raw materials is different, the specific situation is as follows: Table 1: Amount of each component in the preparation of conductive glue Comparative Example 1 A lithium-ion battery negative electrode plate, see attached Figure 1 The basic structure thereof is, from top to bottom, a porous ceramic layer, a conductive layer, a PP-PE composite diaphragm, a conductive layer, and a porous ceramic layer, and is prepared by the following method: S1. Add 5 g of carbon nanotubes and 2 g of metal nanowires to 50 g of ethanol, and disperse them ultrasonically at 20 kHz at 20°C for 30 minutes to form a uniform dispersion. Then, add 20 g of polyvinyl pyrrolidone to the dispersion, stir in a 60°C water bath for 2 hours until completely dissolved, and then place the mixture in a vacuum degassing machine to eliminate bubbles to obtain a conductive adhesive, wherein the metal matrix of the metal nanowires is Cu; S2. The surface of the PP-PE composite membrane was cleaned with ethanol, dried with nitrogen, and placed on the rotary disk of a spin coater. The conductive adhesive was evenly spin-coated on the PP-PE composite membrane at a speed of 2000 rpm to form a conductive layer. The thickness of the conductive layer was measured using a step profiler to ensure that it was within the range of 5-20 nm. After natural drying, the PP-PE composite membrane with a conductive layer was obtained. S3. The porous alumina slurry is evenly coated on the outside of the conductive layer formed above by a doctor blade method, with a thickness controlled at 50 μm. After drying at 80°C for 2 hours, a porous material layer with a pore size of 70 nm is formed. Finally, the electrode is placed in a tablet press and pressed at a pressure of 0.3 MPa for 5 minutes to obtain an integrated structure of the lithium-ion battery negative electrode.

[0028] Comparative Example 2 A lithium-ion battery negative electrode plate, see attached Figure 1 The basic structure thereof is, from top to bottom, a porous ceramic layer, a conductive layer, a PP-PE composite diaphragm, a conductive layer, and a porous ceramic layer, and is prepared by the following method: S1. Add 5 g of carbon nanotubes and 2 g of metal nanowires to 50 g of ethanol, and ultrasonically disperse them at 20 kHz at 20° C. for 30 minutes to form a uniform dispersion. Then, add 20 g of polyvinyl pyrrolidone to the dispersion, stir in a 60° C. water bath for 2 hours until completely dissolved, then add 1 g of 1-ethyl-3-methylimidazolium tetrafluoroborate, continue stirring for 30 minutes, and then place in a vacuum degassing machine to eliminate bubbles to obtain a conductive adhesive, wherein the metal matrix of the metal nanowires is Cu; S2. The surface of the PP-PE composite membrane was cleaned with ethanol, dried with nitrogen, and placed on the rotary disk of a spin coater. The conductive adhesive was evenly spin-coated on the PP-PE composite membrane at a speed of 2000 rpm to form a conductive layer. The thickness of the conductive layer was measured using a step profiler to ensure that it was within the range of 5-20 nm. After natural drying, the PP-PE composite membrane with a conductive layer was obtained. S3. The porous alumina slurry is evenly coated on the outside of the conductive layer formed above by a doctor blade method, with a thickness controlled at 50 μm. After drying at 80°C for 2 hours, a porous material layer with a pore size of 75 nm is formed. Finally, the electrode is placed in a tablet press and pressed at a pressure of 0.3 MPa for 5 minutes to obtain an integrated structure of the lithium-ion battery negative electrode.

[0029] The performance of the negative electrode sheets of lithium batteries prepared in the above embodiments and comparative examples was tested according to the above test methods, and the test results are recorded in the following table.

[0030] Table 2: Performance test results of Examples 1-10 and Comparative Examples 1-2 As can be seen from the above table, the first charge and discharge efficiency of Examples 1-10 is generally high, ranging from 89.5% to 93.3%, among which Example 10 has the highest efficiency, reaching 93.3%, and the first charge and discharge efficiency of Comparative Example 1 is the lowest, which is 88.4%, indicating that the lack of tetraethylammonium tetrafluoroborate may affect the performance of the conductive adhesive, thereby affecting the first charge and discharge efficiency of the battery; the efficiency of Comparative Example 2 is 90.6%, which is higher than Comparative Example 1, but still lower than most examples, indicating that the addition effect of 1-ethyl-3-methylimidazolium tetrafluoroborate is not as good as that of tetraethylammonium tetrafluoroborate.

[0031] The capacity retention rates of Examples 1-10 are also relatively high, ranging from 86.0% to 91.0%. Among them, Example 7 has the highest capacity retention rate, reaching 90.5%, while Comparative Example 1 has the lowest capacity retention rate, at 81.7%, indicating that the battery suffers from significant capacity loss during charge and discharge. The capacity retention rate of Comparative Example 2 is 84.8%, which is higher than that of Comparative Example 1, but still lower than that of other examples, further illustrating the influence of tetraethylammonium tetrafluoroborate on battery performance.

[0032] The capacity attenuation ratios of Examples 1-10 are relatively low, ranging from 9.2% to 11.8%. Among them, the capacity attenuation ratio of Example 7 is the lowest, which is 9.2%. The capacity attenuation ratio of Comparative Example 1 is the highest, which is 15.4%, indicating that the capacity of the battery decays faster during the cycle. The capacity attenuation ratio of Comparative Example 2 is 13.2%.

[0033] The internal resistance of Examples 1-10 is generally low, ranging from 0.62mΩ to 0.69mΩ. Among them, Example 5 has the lowest internal resistance of 0.62mΩ, and Comparative Example 1 has the highest internal resistance of 0.80mΩ, indicating that the internal resistance of the battery is large, which may affect the charge and discharge performance and efficiency of the battery. The internal resistance of Comparative Example 2 is 0.69mΩ.

[0034] In addition, Example 2 used a PP membrane instead of a PP-PE composite membrane, and the performance was slightly reduced, indicating that the PP-PE composite membrane may have better performance. Example 3 used foamed nickel instead of the porous ceramic layer, and the performance was improved, especially in terms of capacity retention and capacity attenuation ratio, indicating that foamed nickel may have better conductivity and stability. Example 4 used MXene instead of the porous ceramic layer, and the performance was similar to that of Example 1, but with slight differences, indicating that MXene is also a potential negative electrode material.

[0035] In Examples 5-10, changes in battery performance were observed by varying the amounts of components in the conductive adhesive. For example, increasing the amount of carbon nanotubes or polyvinyl pyrrolidone may affect battery performance to a certain extent. However, the more the amount, the better the performance. Instead, there is an optimal ratio.

[0036] In summary, the lithium-ion battery negative electrode sheet and its preparation method proposed in this application have achieved remarkable results in structural design and performance optimization, as well as preparation process and cost control. Specifically, the innovative design of using a diaphragm instead of copper foil not only effectively reduces the battery weight and thus improves the energy density, but the integrated diaphragm structure also serves as a current collector, simplifying the battery installation structure. It is worth noting that even when the copper foil layer is omitted, the battery assembled by the electrode can still maintain strong performance. The results of the performance test fully verify these advantages and provide a solid basis for the promotion of this application in practical applications.

[0037] The above are all modifications that a person skilled in the art can make to this embodiment as needed after reading this specification, which do not contribute creatively or solutions that obviously constitute technical inspiration. However, as long as they are within the scope of the claims of this application, they should be protected by patent law.

Claims

1. A lithium-ion battery negative electrode plate, characterized in that: include: a middle polymeric substrate having two opposing sides; A conductive layer is provided on both sides of the intermediate polymer substrate, and the thickness of the conductive layer is 5-20 nm; The porous material layer is disposed on a side of the conductive layer away from the intermediate polymer substrate; The conductive layer is formed by coating a conductive adhesive on both sides of the intermediate polymer substrate by blade coating, spin coating or dip coating. The raw materials for preparing the conductive adhesive include the following components in terms of weight percentage: Polyvinyl pyrrolidone 10%-30%, carbon nanotubes 5%-10%, metal nanowires 1%-5%, ethanol 50%-80%, tetraethylammonium tetrafluoroborate 1-2%.

2. The negative electrode plate of a lithium-ion battery according to claim 1, characterized in that: The porous material layer has a pore size of 70-75 nm and a thickness of 50 μm.

3. The negative electrode plate of a lithium-ion battery according to claim 1, characterized in that: The thickness of the conductive layer is 5-20 nm.

4. The negative electrode plate of a lithium-ion battery according to claim 1, characterized in that: The specific preparation method of the conductive layer is as follows: 1) Preparation of a conductive adhesive: Carbon nanotubes and metal nanowires are added to ethanol and ultrasonically dispersed to form a dispersion. Polyvinyl pyrrolidone is then added to the dispersion and stirred in a water bath until completely dissolved. Tetraethylammonium tetrafluoroborate is then added, stirring is continued, and finally vacuum degassing is performed to obtain a conductive adhesive. 2) Coating of conductive adhesive: First, surface treatment is performed on both sides of the intermediate polymer substrate, and then the intermediate polymer substrate is fixed on the rotary disk of the spin coater. The conductive adhesive is evenly spin-coated onto the intermediate polymer substrate at a certain rate, and a conductive layer is formed after drying.

5. The negative electrode plate of a lithium-ion battery according to claim 1, characterized in that: The substrate of the porous material layer is selected from any one of porous ceramics, metal foam, and MXene.

6. The negative electrode plate of a lithium-ion battery according to claim 1, characterized in that: The material of the intermediate polymer substrate includes at least one of polypropylene and polyethylene.

7. The method for preparing a negative electrode sheet for a lithium-ion battery according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Pre-treating the surface of the intermediate polymer substrate, then preparing a conductive adhesive, coating the conductive adhesive on both sides of the intermediate polymer substrate, and drying to obtain a conductive layer; S2. Compounding the porous material layer with the intermediate polymer substrate with the conductive layer to obtain an integrated composite electrode plate.

8. The method for preparing a negative electrode sheet for a lithium-ion battery according to claim 7, wherein: The pretreatment in step S1 includes at least one of cleaning, surface roughening, and surface modification.

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