A functional current collector and a method for manufacturing the same

Abstract

This invention discloses a functional current collector and its preparation method, relating to the field of lithium battery technology. The method includes the following steps: Step 1: Preparing a spinning solution containing a shape memory polymer, and electrospinning it to obtain a polymer fiber membrane; Step 2: Sequentially subjecting the polymer fiber membrane to gradient carbonization and functionalization treatments to obtain a honeycomb carbon skeleton containing the shape memory polymer; Step 3: Performing pulse electrodeposition on the honeycomb carbon skeleton containing the shape memory polymer to construct helical aluminum fibers and gradient nanowires, obtaining the functional current collector. This application addresses the problem that traditional functional current collectors cannot dynamically adapt to the volume changes of highly expanding electrode materials, providing a functional current collector with "breathing" volume regulation capabilities. Through a triple design of "dynamic skeleton, flexible fiber, and adaptive interface," it achieves long-term buffering against volume expansion of >500%.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically a functional current collector and its preparation method. Background Technology

[0002] With the rapid development of electronic devices, the demand for energy density in lithium-ion batteries is increasing. Among them, silicon-based anodes (4200mAh / g) have a much higher specific capacity than traditional graphite (372mAh / g), and have gradually become a key material for high-energy-density lithium-ion batteries.

[0003] However, further research revealed that silicon-based anodes exhibit volume expansion (>300%) during charging and discharging, severely hindering their application and development. Therefore, existing technologies utilize static porous structures (porosity 60-80%) and continuous aluminum fiber networks in biomimetic honeycomb-fiber functional current collectors to effectively alleviate the expansion stress of silicon-based anodes; however, the following shortcomings still exist: First, because the honeycomb carbon skeleton is a rigid structure with a fixed porosity, it cannot adapt to the dynamic periodic expansion and contraction of the electrode material during cycling, such as the repeated volume changes of the surface during cycling. After long-term cycling, the limited static buffer space is gradually depleted, leading to structural breakage. Second, the interface bonding between the traditional continuous aluminum fiber network and the honeycomb carbon skeleton mainly relies on static mechanical interlocking (such as aluminum whiskers). Under drastic volume changes, the interface concentration can easily cause delamination and desorption, thereby destroying the integrity of the conductive network. Third, the traditional continuous aluminum fiber network is a straight fiber structure with a tensile strain of only 50-100%, which is far lower than the expansion requirement of more than 300% for silicon-based anodes. This causes the traditional continuous aluminum fiber network to break during cycling because it cannot keep up with the deformation of the silicon-based anode.

[0004] In summary, the development of a functional current collector is of great significance in addressing the aforementioned issues. Summary of the Invention

[0005] The purpose of this invention is to provide a functional current collector and its preparation method to solve the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for preparing a functional current collector includes the following steps: Step 1: Prepare a spinning solution containing shape memory polymer, and electrospin it to obtain a polymer fiber membrane; Step 2: The polymer fiber membrane is subjected to gradient carbonization and functionalization treatments in sequence to obtain a honeycomb carbon skeleton containing shape memory polymer; Step 3: Pulse electrodeposition is performed on a honeycomb carbon framework containing shape memory polymer to construct helical aluminum fibers and gradient nanowires, thus obtaining a functional current collector.

[0007] In a more optimized manner, the raw materials of the spinning solution containing the shape memory polymer, by weight percentage, are 8-12% carbon fiber precursor, 5-10% shape memory polymer, 0.3-0.8% conductive additive, and the remainder is N,N-dimethylformamide.

[0008] More preferably, the carbon fiber precursor is polyacrylonitrile; the shape memory polymer includes one of polycaprolactone, polynorbornene, and polyetheretherketone; and the conductive additive includes one of carbon nanotubes and graphene.

[0009] In a more optimized manner, the electrospinning process involves introducing helical orientation through a rotating receiving roller with a rotation speed of 450-550 rpm; the electrospinning voltage is 20-25 KV, the receiving distance is 10-14 cm, and the ambient humidity is 32-40%.

[0010] Ideally, the polymer fiber membrane is a spiral polymer fiber membrane with a diameter of 800~1000nm.

[0011] In a more optimized manner, the gradient carbonization treatment includes a pre-oxidation treatment and a carbonization treatment; the process parameters for the pre-oxidation treatment are: air atmosphere, temperature 200~300℃, heating rate 1.5~2.5℃ / min, and holding time 2~4h; wherein, the purpose of the pre-oxidation treatment is to retain part of the crystalline structure of the shape memory polymer and avoid complete decomposition; The process parameters for the carbonization treatment are as follows: the gas atmosphere is argon, the temperature is 800~1000℃, the heating rate is 4~6℃ / min, and the holding time is 1.5~2.5h; the purpose of the carbonization treatment is to obtain a honeycomb carbon skeleton containing shape memory polymer (porosity of 70%).

[0012] More preferably, the functionalization treatment is plasma treatment; the process parameters of the plasma treatment are: oxygen atmosphere, power of 25~35W, and time of 10~15min; wherein, the purpose of the functionalization treatment (plasma treatment) is to introduce carboxyl groups (-COOH) on the surface of carbon fiber (formed after carbonization of polyacrylonitrile) to enhance the interfacial bonding with aluminum.

[0013] In a more optimized manner, the electrodeposition solution used in the pulse electrodeposition comprises a chloroaluminate ionic liquid composed of aluminum chloride and 1-butyl-3-methylimidazolium chloride, wherein the molar ratio of aluminum chloride to 1-butyl-3-methylimidazolium chloride is (1.1~1.3):1; the electrodeposition solution further comprises 0.08~0.12 wt% citric acid, accounting for 0.08~0.12 wt% of the total mass of the electrodeposition solution; wherein, the role of citric acid is to regulate the deposition rate of aluminum ions in the chloroaluminate ionic liquid.

[0014] More optimally, the process parameters for the pulse electrodeposition are: a forward pulse current of 5~6 mA / cm. 2 The duration is 1.5~2s; the reverse pulse current is 0.8~1mA / cm. 2 The deposition time was 0.4–0.6 s; the temperature was 65–75 °C; and the deposition time was 35–45 min. Helical aluminum fiber growth and gradient nanowire formation were induced by alternating "growth-dissolution" cycles of pulsed current.

[0015] A method for preparing a functional current collector provides a functional current collector in which the honeycomb carbon skeleton containing shape memory polymer has a pore size of 5-50 μm and a pore wall thickness of 1-3 μm; the helical aluminum fiber has a left-handed helical structure with a pitch of 100-300 nm, a diameter of 50-200 nm, and periodic grooves distributed on the fiber surface with a groove depth of 20-50 nm; the gradient nanowire has a root diameter of 200-300 nm, a tip diameter of 50-100 nm, and a length of 1-3 μm.

[0016] In a further embodiment, the honeycomb carbon skeleton containing shape memory polymer is a three-dimensional interconnected honeycomb carbon skeleton. Its pore walls are composed of a composite of "carbon fiber (formed after carbonization of polyacrylonitrile) and shape memory polymer", which has the ability to dynamically adjust porosity: the porosity is 60~70% at room temperature, and can increase to 80~90% when heated (40~60℃, battery operating temperature). After cooling, it automatically shrinks and resets, forming a "expansion-contraction" breathing effect. Among them, the shape memory polymer realizes the expansion and contraction of pore walls through the stretching / folding of helical molecular chains. By designing specific pore diameters and pore wall thicknesses, it has both rigid support and elastic deformation capabilities (maximum tensile strain is 200%).

[0017] In a further embodiment, the spiral aluminum fiber has a left-handed helical structure, and its length can be dynamically adjusted by spiral unwinding / coiling (it can be stretched to twice its original length) while maintaining the continuity of electronic conduction (surface resistance <0.2Ω / sq).

[0018] In a further approach, gradient nanowires grown in situ on the surface of a honeycomb carbon skeleton containing shape memory polymers are modified with hydroxyl groups (-OH) on their surface to form hydrogen bonds with carboxyl groups (-COOH) on the surface of carbon fibers (formed after carbonization of polyacrylonitrile). Combined with the mechanical winding of helical aluminum fibers, a dual "chemical-mechanical" adaptive interface is constructed to reduce the interface delamination phenomenon during cycling.

[0019] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) This application achieves triple dynamic response through the structure of “breathing carbon skeleton, spiral aluminum fiber, gradient nanowire interface”, which increases the volume expansion buffer capacity from 300% to 500% and extends the cycle life of silicon-based anode to 800 times (the traditional functional current collector is 500 times). (2) This application utilizes a dual interface design of chemical hydrogen bonding and mechanical entanglement (three-dimensional spatial interlocking between spiral aluminum fibers and gradient nanowires) to increase the interface bonding strength to 70% (from 50 N / m to 85 N / m), which helps to reduce the cyclic stratification phenomenon and improve the interface stability of the functional current collector. (3) The pulse electrodeposition and gradient carbonization processes in this application are compatible with existing roll-to-roll production lines and are suitable for large-scale production.

[0020] In summary, this application breaks through the limitations of traditional static structures by adopting the concept of "dynamic adaptation". The honeycomb carbon skeleton containing shape memory polymer with adjustable porosity and the self-stretching ability of spiral aluminum fiber greatly improve the cycle stability of high expansion electrode materials. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1: A method for preparing a functional current collector, comprising the following steps: Step 1: Prepare a spinning solution containing shape memory polymer (12% carbon fiber precursor (polyacrylonitrile), 8% shape memory polymer (polycaprolactone), 0.3% conductive additive (graphene), and the remainder is N,N-dimethylformamide. Mix the above raw materials and stir in a water bath at 60°C for 12 hours to form a spinning solution containing shape memory polymer). Electrospin the solution (using a rotating receiving roller at 500 rpm to introduce helical orientation; the electrospinning voltage is 20 kV, the receiving distance is 12 cm, and the ambient humidity is 35%) to obtain a polymer fiber membrane (a helical polymer fiber membrane with a diameter of 900 nm). Step 2: The polymer fiber membrane is subjected to gradient carbonization treatment (gradient carbonization treatment includes pre-oxidation treatment and carbonization treatment; the process parameters for pre-oxidation treatment are: air atmosphere, temperature 280℃, heating rate 2℃ / min, and holding time 3h; the process parameters for carbonization treatment are: argon atmosphere, temperature 1000℃, heating rate 5℃ / min, and holding time 2h, to obtain a carbon skeleton with a porosity of 75% and a polycaprolactone residue of 6wt%) and functionalization treatment (functionalization treatment is plasma treatment; the process parameters for plasma treatment are: oxygen atmosphere, power 30W, and time 10min), to obtain a honeycomb carbon skeleton containing shape memory polymer; Step 3: Perform pulse electrodeposition on the honeycomb carbon framework containing shape memory polymer (the electrodeposition solution used in pulse electrodeposition includes an ionic liquid of chloroaluminate composed of aluminum chloride and 1-butyl-3-methylimidazolium chloride, wherein the molar ratio of aluminum chloride to 1-butyl-3-methylimidazolium chloride is 1.2:1, stirred at 80°C under argon protection for 12 hours to form the chloroaluminate ionic liquid, and then 0.1 wt% citric acid is added and stirred evenly; the process parameters for pulse electrodeposition are: forward pulse current of 6 mA / cm 2 The duration is 1.5s; the reverse pulse current is 0.8mA / cm. 2 (The deposition time was 0.5 s; the temperature was 70 °C; and the deposition time was 40 min), spiral aluminum fibers and gradient nanowires were constructed to obtain a functional current collector; Among them, the functional current collector contains a honeycomb carbon skeleton with a shape memory polymer, which has a pore size of 25 μm and a pore wall thickness of 2 μm; the conductive network of the helical aluminum fiber is a left-handed helical structure, with an aluminum fiber filling amount of 45 vol%, a pitch of 200 nm, a diameter of 125 nm, and periodic grooves distributed on the fiber surface with a groove depth of 35 nm; the gradient diameter aluminum nanowire has a root diameter of 250 nm, a tip diameter of 75 nm, and a length of 2 μm. In the above embodiments, the raw materials were: polyacrylonitrile: molecular weight 150,000, CAS number 25014-41-9, purchased from Sigma-Aldrich / Sinopharm Group; polycaprolactone: CAPA™ 6800, viscosity 1.2 dL / g, CAS number 24980-41-4, purchased from Perstorp / Sigma-Aldrich; graphene: diameter 3 μm, number of layers <10, purchased from Zhongke Leiming (Beijing) Technology Co., Ltd.; aluminum chloride: CAS number 7446-70-0; 1-butyl-3-methylimidazolium chloride: CAS number 79917-90-1; citric acid: CAS number 77-92-9.

[0023] Example 2: A method for preparing a functional current collector, which differs from Example 1 in that 8% shape memory polymer (polycaprolactone) is replaced with 5% shape memory polymer (polyetheretherketone), the carbonization temperature is adjusted to 800℃, and a 0.5μm thick polyimide coating is sprayed after pulse electrodeposition, reducing the limiting bending radius to 1.0mm; Among them, the carbon skeleton with a porosity of 72% and a polyetheretherketone residue of 8wt% is used in the functional current collector. The honeycomb carbon skeleton containing shape memory polymer has a pore size of 30μm and a pore wall thickness of 2.5μm. The conductive network of the helical aluminum fiber is a left-handed helical structure with an aluminum fiber filling amount of 42vol%, a pitch of 180nm, a diameter of 110nm, and periodic grooves distributed on the fiber surface with a groove depth of 30nm. The gradient diameter aluminum nanowire has a root diameter of 220nm, a tip diameter of 80nm, and a length of 1.8μm. In the above embodiments, the raw material is polyetheretherketone with the specification of Evonik VESTAKEEP® Shape Memory; the polyimide coating is PI-2610 type polyamic acid solution, HD MicroSystems.

[0024] Example 3: A method for preparing a functional current collector, differing from Example 1 in that 12% carbon fiber precursor (polyacrylonitrile) is replaced with 10% carbon fiber precursor (polyacrylonitrile), 8% shape memory polymer (polycaprolactone) is replaced with 5% shape memory polymer (polycaprolactone), and 0.3% conductive additive (graphene) is replaced with 0.5% conductive additive (carbon nanotubes); the pre-oxidation temperature is adjusted to 250℃, and the carbonization temperature is adjusted to 900℃; the pulse electrodeposition process parameters are adjusted to: a forward pulse current of 5mA / cm. 2 The duration is 2 seconds; the reverse pulse current is 1 mA / cm². 2 (Time is 0.5s). Among them, the carbon skeleton with a porosity of 73% and a polycaprolactone residue of 7wt% in the functional current collector has a honeycomb carbon skeleton containing shape memory polymer with a pore size of 22μm and a pore wall thickness of 1.8μm; the conductive network of the helical aluminum fiber is a left-handed helical structure with an aluminum fiber filling amount of 40vol%, a pitch of 220nm, a diameter of 130nm, and periodic grooves distributed on the fiber surface with a groove depth of 32nm; the gradient diameter aluminum nanowire has a root diameter of 240nm, a tip diameter of 70nm, and a length of 2.2μm; In the above embodiments, the raw material is carbon nanotubes, specifically multi-walled carbon nanotubes, with catalog number C805983, ID: 5nm, OD: 30nm, and Length: 10μm.

[0025] Example 4: A method for preparing a functional current collector, which differs from Example 1 in that the 8% shape memory polymer (polycaprolactone) is adjusted to 8% shape memory polymer (polynorbornene), and the carbonization temperature is adjusted to 950℃. Among them, the carbon skeleton with a porosity of 74% and a residual polynorbornene content of 6.5wt% in the functional current collector has a honeycomb carbon skeleton containing shape memory polymer with a pore size of 24μm and a pore wall thickness of 2.1μm; the conductive network of the helical aluminum fiber is a left-handed helical structure with an aluminum fiber filling amount of 44vol%, a pitch of 190nm, a diameter of 120nm, and periodic grooves distributed on the fiber surface with a groove depth of 33nm; the gradient diameter aluminum nanowire has a root diameter of 245nm, a tip diameter of 78nm, and a length of 2.1μm; In the above embodiments, the raw material is polynorbornene with a specification of Rimtec Norsorex®.

[0026] Example 5: A method for preparing a functional current collector, which differs from Example 1 in that the spinning solution containing the shape memory polymer in Example 5 comprises 8% carbon fiber precursor, 10% shape memory polymer, 0.3% conductive additive, and the remainder is N,N-dimethylformamide. Among them, the carbon skeleton with a porosity of 76% and a polycaprolactone residue of 9wt% is used in the functional current collector. The honeycomb carbon skeleton containing shape memory polymer has a pore size of 28μm and a pore wall thickness of 2.3μm. The conductive network of the helical aluminum fiber is a left-handed helical structure with an aluminum fiber filling amount of 46vol%, a pitch of 170nm, a diameter of 105nm, and periodic grooves distributed on the fiber surface with a groove depth of 28nm. The gradient diameter aluminum nanowire has a root diameter of 230nm, a tip diameter of 85nm, and a length of 1.9μm.

[0027] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 directly uses conventional aluminum foil to replace the functional current collector.

[0028] Comparative Example 2: The difference from Example 1 is that Comparative Example 2 uses direct current electrodeposition instead of pulse electrodeposition, so that the aluminum fibers are straight fibers without helical pitch (lacking helical fibers). Among them, the carbon skeleton with a porosity of 75% and a polyether ether ketone residue of 6wt% is used in the functional current collector. The honeycomb carbon skeleton containing shape memory polymer has a pore size of 25μm and a pore wall thickness of 2μm. The fiber surface has no periodic grooves. The root diameter of the gradient diameter aluminum nanowire is 250nm, the tip diameter is 75nm, and the length is 2μm.

[0029] Comparative Example 3: The difference from Example 1 is that Comparative Example 2 does not contain shape memory polymer (lacking dynamic porosity). Among them, the functional current collector contains a honeycomb carbon skeleton with a shape memory polymer, which has a pore size of 25 μm and a pore wall thickness of 2 μm; the conductive network of the helical aluminum fiber is a left-handed helical structure, with an aluminum fiber filling amount of 45 vol%, a pitch of 200 nm, a diameter of 125 nm, and periodic grooves distributed on the fiber surface with a groove depth of 35 nm; the gradient diameter aluminum nanowire has a root diameter of 250 nm, a tip diameter of 75 nm, and a length of 2 μm.

[0030] Performance Test 1: The functional current collectors prepared in Examples 1-5 and Comparative Examples 1-3 were tested for performance indicators, including maximum volume expansion buffer rate, silicon anode cycle life, helical fiber tensile strain, interfacial bonding strength, and surface resistance. The test results are shown in Table 1. Note: "—" indicates that the comparative example (traditional aluminum foil) does not have a spiral fiber structure, and therefore does not have this performance indicator; Table 1

[0031] Conclusion: As shown in Table 1 above, this application addresses the problem that traditional functional current collectors cannot dynamically adapt to the volume changes of highly expandable electrode materials. It provides a functional current collector with "breathing" volume regulation capabilities, achieving long-term buffering against volume expansion of >500% through a triple design of "dynamic skeleton, flexible fiber, and adaptive interface." In Example 1, a highly conductive skeleton is obtained through carbonization treatment (1000℃), and electrodeposition parameters are optimized to improve the volume expansion buffering rate (500%) and long cycle life (800 cycles), providing a high-capacity silicon-based anode design. In Example 2, by reducing the carbonization temperature to 800℃, the elastic groups in the polymer chain (shape memory polymer) are effectively preserved, giving the carbon skeleton higher intrinsic flexibility. An additional 0.5μm polyimide coating is applied, thereby reducing the limiting bending radius to 1.0mm, suitable for applications with extremely high flexibility requirements. Compared to the comparative example, this application achieves a leap from "static passive support" to "dynamic active adaptation" through the above triple dynamic design.

[0032] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a functional current collector, characterized in that: Includes the following steps: Step 1: Prepare a spinning solution containing shape memory polymer, and electrospin it to obtain a polymer fiber membrane; Step 2: The polymer fiber membrane is subjected to gradient carbonization and functionalization treatments in sequence to obtain a honeycomb carbon skeleton containing shape memory polymer; Step 3: Pulse electrodeposition is performed on a honeycomb carbon framework containing shape memory polymer to construct helical aluminum fibers and gradient nanowires, thus obtaining a functional current collector.

2. The method for preparing a functional current collector according to claim 1, characterized in that: The raw materials of the spinning solution containing the shape memory polymer, by weight percentage, are 8-12% carbon fiber precursor, 5-10% shape memory polymer, 0.3-0.8% conductive additive, and the remainder is N,N-dimethylformamide.

3. The method for preparing a functional current collector according to claim 2, characterized in that: The carbon fiber precursor is polyacrylonitrile; the shape memory polymer includes one of polycaprolactone, polynorbornene, and polyetheretherketone; the conductive additive includes one of carbon nanotubes and graphene.

4. The method for preparing a functional current collector according to claim 1, characterized in that: In the electrospinning process, a spiral orientation is introduced by a rotating receiving roller with a rotation speed of 450~550rpm; the voltage of electrospinning is 20~25KV, the receiving distance is 10~14cm, and the ambient humidity is 32~40%.

5. The method for preparing a functional current collector according to claim 1, characterized in that: The polymer fiber membrane is a spiral polymer fiber membrane with a diameter of 800~1000nm.

6. The method for preparing a functional current collector according to claim 1, characterized in that: The gradient carbonization treatment includes a pre-oxidation treatment and a carbonization treatment. The process parameters for the pre-oxidation treatment are: air atmosphere, temperature 200~300℃, heating rate 1.5~2.5℃ / min, and holding time 2~4h. The process parameters for the carbonization treatment are: argon atmosphere, temperature 800~1000℃, heating rate 4~6℃ / min, and holding time 1.5~2.5h.

7. The method for preparing a functional current collector according to claim 1, characterized in that: The functionalization process is plasma treatment; the process parameters of the plasma treatment are: oxygen atmosphere, power of 25~35W, and time of 10~15min.

8. The method for preparing a functional current collector according to claim 1, characterized in that: The electrodeposition solution used in the pulse electrodeposition includes an ionic liquid of chloroaluminate composed of aluminum chloride and 1-butyl-3-methylimidazolium chloride, wherein the molar ratio of aluminum chloride to 1-butyl-3-methylimidazolium chloride is (1.1~1.3):1; the electrodeposition solution also includes citric acid accounting for 0.08~0.12 wt% of the total mass of the electrodeposition solution.

9. The method for preparing a functional current collector according to claim 1, characterized in that: The process parameters for pulse electrodeposition are: forward pulse current of 5~6 mA / cm. 2 The duration is 1.5~2s; the reverse pulse current is 0.8~1mA / cm. 2 The deposition time is 0.4~0.6s; the temperature is 65~75℃; and the deposition time is 35~45min.

10. The functional current collector prepared by the method according to any one of claims 1 to 9, characterized in that: In the functional current collector, the honeycomb carbon skeleton containing shape memory polymer has a pore size of 5~50μm and a pore wall thickness of 1~3μm; the spiral aluminum fiber has a left-handed helical structure with a pitch of 100~300nm, a diameter of 50~200nm, and periodic grooves distributed on the fiber surface with a groove depth of 20~50nm; the gradient nanowire has a root diameter of 200~300nm, a tip diameter of 50~100nm, and a length of 1~3μm.

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