A high-power titanium-based lithium-ion capacitor and a preparation method thereof

Abstract

The application discloses a high-power titanium-based lithium ion capacitor and a preparation method thereof, and belongs to the technical field of electrochemical energy storage devices, and aims to solve the problem of limitation of the overall power and cycle stability of the capacitor due to the mismatch of the kinetic performance of the positive and negative electrodes. The capacitor comprises a positive electrode sheet, a negative electrode sheet, a diaphragm and an electrolyte. The negative electrode sheet comprises a titanium-based negative electrode material coated with nano-carbon and modified by ion doping; the positive electrode sheet comprises an activated carbon electrode material, the activated carbon has micropores and mesopores, and the volume ratio of the micropores to the mesopores is 3:1 to 5:1. By matching the positive electrode with fast kinetics and the high-performance negative electrode, the kinetic performance of the positive and negative electrodes is coordinated, and the'short board effect' is solved. The application also provides a corresponding preparation method. The capacitor has excellent rate performance and cycle stability.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage device technology, and in particular to a high-power titanium-based lithium-ion capacitor and its preparation method. Background Technology

[0003] Lithium-ion capacitors (LICs) are a novel energy storage device that combines the high power density of double-layer capacitors with the high energy density of lithium-ion batteries, and have broad application prospects. To improve device safety, current technologies often use titanium-based materials (such as lithium titanate) with high lithium intercalation potentials as the negative electrode to avoid the risk of lithium dendrite formation. Simultaneously, to overcome the low intrinsic electronic conductivity of titanium-based materials, modification strategies such as nano-carbon coating and ion doping are commonly employed to improve the rate performance of the negative electrode.

[0004] However, while optimizing the performance of the negative electrode, existing technologies often neglect corresponding improvements to the positive electrode, which still commonly uses traditional microporous activated carbon materials. This type of activated carbon has a simple pore structure. Although the micropores provide a high specific surface area, during high-current charge and discharge, the narrow micropores, acting as the main channels for ion transport, lead to severe ion transport obstruction and concentration polarization, resulting in the positive electrode's kinetic performance being far inferior to that of the optimized negative electrode. This mismatch in the kinetic performance of the positive and negative electrodes—a "bottleneck effect"—has become a core bottleneck restricting the overall power performance and cycle stability of lithium-ion capacitors. Summary of the Invention

[0006] One objective of this invention is to provide a high-power titanium-based lithium-ion capacitor and its preparation method, aiming to solve the technical problem in the prior art that the mismatch between the dynamic performance of the positive and negative electrodes limits the overall power performance and cycle stability of lithium-ion capacitors.

[0007] To achieve the above objectives, this invention provides a high-power titanium-based lithium-ion capacitor, comprising a positive electrode, a negative electrode, a separator, an electrolyte, and a sealed casing. The negative electrode comprises a titanium-based negative electrode material coated with nano-carbon and modified by ion doping; the positive electrode comprises an activated carbon electrode material, wherein the activated carbon in the activated carbon electrode material has micropores and mesopores, and the volume ratio of the micropores to the mesopores is 3:1 to 5:1; the kinetic performance of the positive and negative electrodes is matched, ensuring that the capacitor retains at least 92% of its capacity after 10,000 cycles at 10C. By coating the negative electrode material with nano-carbon and modifying it with ion doping, the electronic conductivity and structural stability of the negative electrode can be significantly improved, thereby obtaining excellent negative electrode kinetic performance. Simultaneously, by precisely controlling the volume ratio of micropores to mesopores in the positive electrode activated carbon material, a highly efficient hierarchical pore network of "micropore charge storage and mesopore transport" is constructed. The presence of mesopores provides a low-resistance channel for the rapid transport of electrolyte ions, significantly improving the kinetic performance of the positive electrode. By matching the positive electrode with fast dynamics to the high-performance negative electrode, the dynamic performance of the positive and negative electrodes is synergistic, fundamentally solving the "bottleneck effect" and thus enabling the capacitor to exhibit excellent rate performance and cycle stability as a whole.

[0008] Optionally, the titanium-based anode material is selected from one or more combinations of lithium titanate, titanium-based lithium vanadium oxide, fluorine-doped lithium titanate, and lithium titanate-based composite oxide. These materials have suitable lithium intercalation potentials and stable structures, making them excellent choices for constructing high-performance anodes.

[0009] Optionally, the active grain size of the titanium-based anode material is 50-200 nm. Controlling the active grain size at the nanoscale can effectively shorten the diffusion path of lithium ions in the solid phase, further improving the rate performance of the anode.

[0010] Optionally, the compaction density of the negative electrode is 1.6-2.4 g / cm³, and the compaction density of the positive electrode is 0.5-0.9 g / cm³, with the ratio of the compaction density of the negative electrode to that of the positive electrode being 1.8:1 to 4.8:1. Using a relatively high compaction density for the negative electrode helps to increase the volumetric energy density of the capacitor, while using a relatively loose compaction density for the positive electrode helps to retain sufficient porosity, providing space for the rapid transport of electrolyte ions. This synergistic design of compaction densities is key to ensuring both high power performance and high energy density.

[0011] Optionally, the electrolyte is a 1 mol / L lithium hexafluorophosphate electrolyte, and its solvent is a carbonate solvent containing at least one of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. This electrolyte system exhibits good ionic conductivity and an electrochemical window, allowing for good matching with both positive and negative electrode materials.

[0012] This invention also provides a method for preparing a high-power titanium-based lithium-ion capacitor, comprising the following steps: providing a negative electrode sheet comprising a titanium-based negative electrode material coated with nano-carbon and modified by ion doping; providing a positive electrode sheet comprising an activated carbon electrode material, wherein the activated carbon in the activated carbon electrode material has micropores and mesopores, and the volume ratio of the micropores to the mesopores is 3:1 to 5:1; providing a separator and an electrolyte; assembling the negative electrode sheet, the positive electrode sheet, and the separator, and encapsulating them after injecting the electrolyte; wherein the kinetic performance of the positive electrode sheet and the negative electrode sheet is matched so that the capacitor retains no less than 92% of its capacity after 10,000 cycles at a 10C rate.

[0013] Optionally, the step of providing the negative electrode sheet includes: mixing the titanium-based negative electrode material, conductive agent, and binder in a mass ratio of 90-92:3-5:3-6 to prepare a negative electrode slurry, and then coating the negative electrode slurry onto a current collector and drying it to obtain the negative electrode sheet; and the step of providing the positive electrode sheet includes: mixing the activated carbon, conductive agent, and binder in a mass ratio of 88-90:3-4:4-6 to prepare a positive electrode slurry, and then coating the positive electrode slurry onto a current collector and drying it to obtain the positive electrode sheet.

[0014] Optionally, after drying, the process further includes a rolling step of pressing the negative electrode and the positive electrode to achieve a compaction density of 1.6-2.4 g / cm³ for the negative electrode and 0.5-0.9 g / cm³ for the positive electrode. The rolling step allows for precise control of the electrode's compaction density and porosity, and is a key process for achieving the aforementioned optimized electrode physical structure.

[0015] Optionally, the process also includes an aging and activation step after encapsulation, which includes charging to 3.0V at a constant current of 0.2C, then disconnecting the circuit and allowing it to stand for 2 hours. This aging and activation step facilitates the formation of a stable and uniform solid electrolyte interphase (SEI) film on the electrode surface, especially on the negative electrode surface. This is crucial for suppressing side reactions and improving the capacitor's initial coulombic efficiency and long-term cycling stability.

[0016] Optionally, the encapsulation step is performed under a vacuum pressure of -0.08 MPa to -0.1 MPa. Encapsulation and electrolyte injection in a vacuum environment helps the electrolyte to fully wet the pores of the electrodes and separator, eliminates air bubbles, and ensures good ion conduction pathways inside the capacitor.

[0017] Compared with existing technologies, this invention has the following beneficial effects: 1. By optimizing the pore structure of the positive electrode activated carbon and matching it with the modified high-performance titanium-based negative electrode, synergistic performance of the positive and negative electrode dynamics is achieved, fundamentally solving the "bottleneck effect" caused by electrode performance mismatch and significantly improving the overall performance of the lithium-ion capacitor. 2. Thanks to the effective matching of positive and negative electrode dynamics, the capacitor of this invention has both high power performance and long cycle life. After 10,000 cycles at a high rate of 10C, the capacity retention rate is still not less than 92%, solving the technical problem of difficulty in achieving both high power and long cycle life. 3. While achieving high power and long life, the intrinsic high safety of the titanium-based negative electrode is retained, and through synergistic optimization of electrode compaction density, the capacitor achieves high energy density and good comprehensive performance. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of a high-power titanium-based lithium-ion capacitor according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the microstructure of the negative electrode material according to an embodiment of the present invention. Figure 3 This is a schematic diagram of the microstructure of the cathode material according to an embodiment of the present invention. Figure 4 This is a flowchart of a method for preparing a high-power titanium-based lithium-ion capacitor according to an embodiment of the present invention. Figure 5 This is a schematic diagram comparing the performance of an embodiment of the present invention with that of a comparative example.

[0021] In the figure: 10-positive electrode current collector, 11-positive electrode active material layer, 20-separator, 30-negative electrode active material layer, 31-negative electrode current collector, 50-sealing shell, 111-mesopore, 112-micropore, 113-carbon matrix framework, 301-titanium-based material matrix, 302-lattice doped ions, 303-surface nano-carbon coating layer. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. The described embodiments should not be considered as limitations on this application. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application. Unless otherwise defined, all technical and scientific terms used in the embodiments of this application have the same meaning as commonly understood by those skilled in the art. The terminology used in the embodiments of this application is for the purpose of describing the embodiments of this application only and is not intended to limit this application. Before further detailed description of the embodiments of this application, the nouns and terms involved in the embodiments of this application are explained, and the nouns and terms involved in the embodiments of this application are subject to the following interpretations.

[0024] (1) Lithium-ion capacitor (LIC): refers to a new type of hybrid energy storage device that combines the advantages of high power density of double-layer capacitor and high energy density of lithium-ion battery. Its working principle usually involves the Faraday reaction of lithium insertion / extraction on one electrode (such as negative electrode) and the physical adsorption / desorption of ions by non-Faraday process on the other electrode (such as positive electrode).

[0025] (2) Kinetic performance matching: This refers to the coordinated design of the positive and negative electrodes of a capacitor to ensure that the ion / electron transport capabilities (kinetic performance) of the positive and negative electrodes are at a basically equivalent level, thereby avoiding the limitation of the overall device performance due to the poor performance of one electrode. In this application, it specifically refers to optimizing the pore structure of the positive electrode and the material structure of the negative electrode so that the ion diffusion impedance and electron conduction impedance of both are on the same order of magnitude under high current charging and discharging conditions, thereby achieving "current homogenization" inside the entire device and eliminating the performance degradation caused by local polarization, that is, eliminating the "bottleneck effect".

[0026] (3) Aging activation: refers to the process of forming a stable and uniform solid electrolyte interface film (SEI film) on the electrode surface after the capacitor is packaged by a specific charge and discharge regime (e.g., low-rate constant current charging followed by resting). This process helps to improve the initial coulombic efficiency and long-term cycle stability of the capacitor.

[0027] Please see Figure 1 This application provides a high-power titanium-based lithium-ion capacitor, aiming to solve the technical problem in the prior art where insufficient positive electrode kinetic performance leads to a kinetic mismatch between the positive electrode and the high-performance negative electrode, thereby limiting the overall power performance and cycle stability of the device. The basic structure of the capacitor includes a positive electrode, a negative electrode, a separator 20 placed between the two, an electrolyte impregnating the above components, and a sealed housing 50 for accommodating and sealing all internal components.

[0028] The core technical solution of this application lies in the synergistic design of the positive and negative electrodes. Specifically, the negative electrode sheet comprises a specially modified titanium-based negative electrode material. This modification includes two aspects: first, ion doping of the lattice of the titanium-based material, such as... Figure 2 As shown, lattice-doped ions 302 are introduced into the lattice structure of the titanium-based material matrix 301. The purpose of this design is to increase the carrier concentration or defect sites within the material by introducing heterovalent ions or changing lattice parameters, thereby improving the ionic and electronic conductivity of the titanium-based material and overcoming its inherent poor conductivity. Secondly, a nano-carbon coating layer 303 is formed on the surface of the ion-doped titanium-based material particles. The purpose of this design is to construct a continuous and efficient conductive network between the particles, further reducing the overall electron transport impedance of the electrode and buffering volume changes during charge and discharge, thus improving structural stability. Through this dual modification of ion doping and nano-carbon coating, the rate performance and cycle life of the negative electrode are significantly improved.

[0029] Corresponding to the aforementioned high-performance negative electrode, this application also provides targeted optimizations to the positive electrode. The positive electrode comprises an activated carbon electrode material. For example... Figure 3 As shown, the special feature of this activated carbon electrode material lies in its internal pore structure. Micropores 112 and mesopores 111 are simultaneously distributed on its carbon matrix framework 113. Existing activated carbon typically consists mainly of micropores, which, while providing a high specific surface area, are too tortuous and narrow as ion transport channels, easily causing ion congestion under high current and resulting in significant transport impedance. The technical solution of this application constructs a highly efficient hierarchical pore network of "micropore charge storage and mesopore transport" by precisely controlling the volume ratio of the micropores 112 to the mesopores 111 to 3:1 to 5:1. The high specific surface area of ​​the micropores 112 primarily adsorbs electrolyte ions to store charge, ensuring high capacity; while the larger pore size of the mesopores 111 constitutes a fast ion transport highway penetrating the electrode, ensuring that electrolyte ions can quickly reach the micropore surface. Through this synergistic effect, the ion transport impedance of the positive electrode is significantly reduced, improving its kinetic performance.

[0030] By combining the aforementioned fast-dynamic positive electrode with a dual-modified high-performance negative electrode, the kinetic performance of the positive and negative electrodes is matched. This matching ensures that both the positive and negative electrodes can smoothly complete the transport of ions and electrons during high-rate charge and discharge, without the performance bottleneck of one electrode limiting the performance of the entire device. By solving the "bottleneck effect" of positive and negative electrode kinetics commonly found in the prior art, the capacitor provided in this application can maintain a capacitance retention of no less than 92% even after 10,000 rapid charge and discharge cycles at a high rate of 10C under stringent testing conditions, demonstrating its excellent power performance and good cycle stability.

[0031] Furthermore, in a preferred embodiment, to further optimize the performance of the negative electrode, the titanium-based negative electrode material can be selected from one or more combinations of lithium titanate, titanium-based lithium vanadium oxide, fluorine-doped lithium titanate, and lithium titanate-based composite oxide. These materials all have high lithium intercalation potentials, which can fundamentally prevent the precipitation of lithium dendrites and ensure the intrinsic safety of the capacitor. For example, lithium titanate (… As a titanium-based matrix, 301 exhibits "zero strain" characteristics, resulting in minimal lattice volume change during lithium insertion / extraction, which contributes to achieving ultra-long cycle life. Choosing titanium-based lithium vanadium oxide can provide even higher theoretical capacity. By ion doping and nano-carbon coating of these basic materials, anode materials with excellent overall performance can be obtained.

[0032] In another preferred embodiment, the active grain size of the titanium-based anode material is controlled within the range of 50-200 nm. Nanostructuring the material significantly shortens the diffusion path of lithium ions within the solid-phase particles, which is another important means of improving the material's rate performance. When the particle size is less than 50 nm, the specific surface area of ​​the material is too large, which may lead to increased side reactions with the electrolyte, affecting initial efficiency and cycle stability. Conversely, when the particle size is greater than 200 nm, the diffusion path of ions within the solid phase becomes longer, which is not conducive to rapid insertion and extraction under high current, limiting its kinetic performance. Therefore, controlling the particle size within the range of 50-200 nm achieves a good balance between ensuring high rate performance and maintaining good cycle stability.

[0033] In one alternative implementation, the macroscopic physical structure of the electrodes was also synergistically optimized. Specifically, the compaction density of the negative electrode was controlled at 1.6-2.4 g / cm³, while the compaction density of the positive electrode was controlled at 0.5-0.9 g / cm³. Furthermore, the ratio of the compaction density of the negative electrode to that of the positive electrode was controlled within the range of 1.8:1 to 4.8:1. The principle behind this design is that the energy density of the negative electrode, as a Faraday electrode, is directly related to the amount of active material filled; therefore, using a relatively high compaction density (1.6-2.4 g / cm³) helps to improve the overall volumetric energy density of the device. Conversely, the performance of the positive electrode, as a non-Faraday electrode, relies more on the rapid transport of ions within the pores; therefore, using a relatively loose compaction density (0.5-0.9 g / cm³) can retain sufficient porosity, providing channels for the rapid migration of electrolyte ions and ensuring high power performance. By precisely controlling the ratio of positive and negative electrode compaction densities, a good balance between energy density and power density was achieved.

[0034] Furthermore, the electrolyte can be lithium hexafluorophosphate with a concentration of 1 mol / L (… The electrolyte is a carbonate solvent containing at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). This type of electrolyte has a wide electrochemical window and good ionic conductivity, enabling it to be well-matched with the positive and negative electrode materials designed in this application, jointly constructing a high-performance electrochemical energy storage system.

[0035] Please see Figure 4 This application also provides a method for preparing the aforementioned high-power titanium-based lithium-ion capacitor. This method aims to reliably convert the aforementioned electrode material with a specific structural design into a capacitor product with good performance. The method first includes a step of providing a negative electrode sheet comprising the aforementioned nano-carbon-coated and ion-doped modified titanium-based negative electrode material. Simultaneously, it includes a step of providing a positive electrode sheet comprising the aforementioned activated carbon electrode material, wherein the activated carbon has a specific micropore to mesopore volume ratio (3:1 to 5:1). This is the basis for ensuring the performance of the final product.

[0036] Subsequently, commercially available separators and electrolytes are provided. Then, in a dry environment, the negative electrode, the positive electrode, and the separator placed between them are stacked or wound to form a battery cell. This process corresponds to... Figure 4 The process involves cutting and assembling (S30). Afterwards, the battery cell is placed into the sealed housing 50, where electrolyte is injected and final encapsulation is performed. This process corresponds to... Figure 4 The encapsulation and electrolyte filling process is described in section S40. The core of this method lies in ensuring the matching of positive and negative electrode dynamics in the fabricated capacitor through the use of co-designed positive and negative electrodes, thereby achieving the desired higher power and longer cycle life.

[0037] Furthermore, in a preferred embodiment, the steps of providing the negative and positive electrode plates can be more specific. For example, in Figure 4 In step S10 of the slurry preparation, the step of providing the negative electrode sheet may include: mixing the titanium-based negative electrode material, carbon black or carbon nanotubes as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in an N-methylpyrrolidone (NMP) solvent at a mass ratio of 90-92:3-5:3-6 to prepare a uniform negative electrode slurry. Similarly, the step of providing the positive electrode sheet may include: mixing the activated carbon with a specific pore structure, the conductive agent, and the binder in a mass ratio of 88-90:3-4:4-6 to prepare a positive electrode slurry. By optimizing the slurry ratio, it can be ensured that the active material forms a stable and highly conductive three-dimensional network structure in the electrode.

[0038] In another preferred embodiment, after the slurry is coated onto the current collector and dried, i.e. Figure 4The coating and rolling step S20 further includes a rolling step for the negative electrode and the positive electrode. The purpose of this step is to precisely control the thickness and porosity of the electrodes, so that the compaction density of the negative electrode reaches the aforementioned 1.6-2.4 g / cm³, and the compaction density of the positive electrode reaches the aforementioned 0.5-0.9 g / cm³. Through the rolling process, precise control of the macroscopic physical structure of the electrodes can be achieved, which is a key process for achieving coordinated matching of the compaction densities of the positive and negative electrodes.

[0039] In an optional embodiment, the preparation method further includes an aging and activation step after encapsulation, which corresponds to... Figure 4 The aging activation process, S50, involves: charging the packaged capacitor with a small current of 0.2C until its voltage reaches the upper limit of the operating voltage (e.g., 3.0V), then disconnecting the circuit and allowing it to stand for 2 hours. The purpose of this process is to slowly and uniformly form a dense solid electrolyte interphase (SEI) film on the negative electrode surface. A high-quality SEI film effectively inhibits the continued decomposition of the electrolyte in subsequent cycles, which is crucial for reducing interfacial impedance, improving coulombic efficiency, and extending the cycle life of the capacitor.

[0040] Furthermore, to ensure sufficient electrolyte filling and effective venting of internal gas, the encapsulation step can be performed under a vacuum pressure of -0.08 MPa to -0.1 MPa. Encapsulation and electrolyte filling under vacuum conditions ensure that the electrolyte can completely wet all pores inside the electrodes and separator, avoiding the formation of "dead zones" due to residual gas that could affect the performance and consistency of the capacitor.

[0041] To illustrate the technical solution of this invention more specifically, several specific embodiments are provided below. The performance limit of a lithium-ion capacitor is not determined by a single electrode, but rather by the electrode with the worse kinetic performance. The ion diffusion coefficient of the positive electrode (single microporous activated carbon) of a traditional lithium-ion capacitor (LIC) is much lower than that of a modified titanium-based negative electrode, causing the positive electrode to become a bottleneck under high current. From a systems theory perspective, by precisely controlling the mesoporous / microporous ratio of the positive electrode, its effective ion diffusion coefficient can be significantly improved, allowing the kinetic performance of the positive electrode to match that of the high-performance negative electrode. This matching makes the ion diffusion impedance of the positive and negative electrodes reach the same order of magnitude, thereby achieving "current homogenization" throughout the entire device and avoiding local overcharging / over-discharging. This is the fundamental reason why this invention achieves high cycle stability.

[0042] In one specific embodiment, a high-power titanium-based lithium-ion capacitor is fabricated. The negative electrode uses a titanium-based negative electrode material of nano-carbon coated lithium titanate (…). Its active crystal grains have a diameter of 100 nm. (Refer to...) Figure 2The titanium-based material matrix 301 is lithium titanate, and a surface nano-carbon coating layer 303 is formed on its surface. After rolling, the compaction density of the negative electrode is 1.9 g / cm3. The positive electrode uses activated carbon electrode material, and the volume ratio of micropores 112 to mesopores 111 is 4:1, which is within the preferred range of 3:1 to 5:1 defined in this invention. After rolling, the compaction density of the positive electrode is 0.8 g / cm3. The ratio of the negative electrode compaction density to the positive electrode compaction density is 2.375:1, which is within the range of 1.8:1 to 4.8:1. The electrolyte uses lithium hexafluorophosphate with a concentration of 1 mol / L. The electrolyte is dissolved in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. Following the aforementioned preparation method, a positive electrode sheet comprising a positive current collector 10 and a positive active material layer 11, a negative electrode sheet comprising a negative current collector 31 and a negative active material layer 30, and a separator 20 are assembled, injected with electrolyte, and then sealed in a sealed outer casing 50, followed by aging and activation treatment.

[0043] In another preferred embodiment, the negative electrode material is lithium titanate coated with nano-carbon and modified with fluorine doping, with an active grain size of 150 nm. The compaction density of the negative electrode sheet is controlled at 2.0 g / cm³. The positive electrode sheet is activated carbon with a micropore to mesopore volume ratio of 3:1 and a compaction density of 0.85 g / cm³. Other components and preparation processes are the same as in the aforementioned embodiments. This embodiment verifies the technical effects of different types of ion doping and different combinations of positive electrode porosity ratios.

[0044] In another preferred embodiment, the negative electrode material is a titanium-based lithium vanadium oxide coated with nano-carbon and modified with niobium doping, with an active grain size of 80 nm. The compaction density of the negative electrode sheet is 1.95 g / cm³. The positive electrode sheet is activated carbon with a micropore to mesopore volume ratio of 5:1, and a compaction density of 0.75 g / cm³. Other components and preparation processes are the same as in the aforementioned embodiments. This embodiment verifies the technical effects of different titanium-based material systems and different combinations of positive electrode porosity ratios.

[0045] In contrast, a comparative example that does not meet the specific limitations of this invention is provided. This comparative example differs from the first specific embodiment only in that its positive electrode uses conventional microporous activated carbon, with a micropore volume ratio as high as 85% and a mesopore volume ratio of only 15%, resulting in a micropore to mesopore volume ratio of approximately 5.67:1, exceeding the 3:1 to 5:1 range defined in this invention. This pore structure lacks effective rapid ion transport channels, leading to poor positive electrode kinetic performance.

[0046] As another comparison, a second comparative example is provided. This comparative example differs from the first specific embodiment only in that its negative electrode uses unmodified pure lithium titanate material, i.e., without ion doping and nano-carbon coating. This negative electrode material has very low intrinsic electronic conductivity and ionic conductivity, resulting in poor negative electrode kinetic performance.

[0047] As another comparison, a third comparative example is provided. This comparative example differs from the first specific embodiment in that, although its negative electrode uses nano-carbon coated and ion-doped modified lithium titanate, its positive electrode has a micropore to mesopore volume ratio of 6:1, which also exceeds the 3:1 to 5:1 range defined in this invention. This is used to verify the critical significance of the parameter range defined in this invention.

[0048] The capacitors prepared according to the above three specific embodiments (hereinafter referred to as Examples 1-3) and three comparative examples (hereinafter referred to as Comparative Examples 1-3) were subjected to performance tests under the same conditions (25℃, 1.5-3.0V voltage range), and the results are shown in the table below:

[0049] The technical effects of this invention are clearly evident from the performance test results above. Firstly, by comparing Example 1 with Comparative Examples 1 and 2, the synergistic effect proposed in this invention can be verified. Comparative Example 1 exhibits excellent negative electrode performance but poor positive electrode performance; Comparative Example 2 has an optimized positive electrode structure but an unmodified negative electrode. The power densities (10.2 kW / kg and 9.8 kW / kg, respectively) and cycle performances (76.2% and 71.4%, respectively) of both are significantly lower than those of Example 1 (power density 15.2 kW / kg, cycle retention 92.3%). This fully demonstrates that only when the fast dynamic structure of the positive electrode and the high-performance modified structure of the negative electrode simultaneously meet the design requirements of this invention can a synergistic effect be achieved, resulting in excellent overall performance.

[0050] Secondly, by comparing Examples 1-3 with Comparative Examples 1 and 3, the criticality of the positive electrode micropore / mesopore volume ratio range defined in this invention can be verified. The ratios in Comparative Examples 1 and 3 (5.67:1 and 6:1, respectively) both exceed the 3:1 to 5:1 range defined in this invention. Although their power density and cycle retention are better than Comparative Example 2, which has the worst negative electrode performance, they are still significantly lower than all other examples. This indicates that only by precisely controlling the pore ratio within the 3:1 to 5:1 window can the most efficient ion transport network be constructed, achieving optimal kinetic matching with a high-performance negative electrode, thereby obtaining the technical effects of higher power and longer cycle life, such as… Figure 5 The performance comparison diagram shown demonstrates that the numerical range defined in this invention is not a simple, conventional choice, but rather the key to achieving the invention's objective.

[0051] In summary, this invention solves the long-standing problem of positive and negative electrode kinetic mismatch in the field of lithium-ion capacitors by synergistic design and precise control of the positive electrode pore structure and the negative electrode microstructure. While maintaining high energy density and high safety, it significantly improves the power density and cycle stability of the device.

[0052] The high-power titanium-based lithium-ion capacitor provided by this invention, due to its combination of high power, high energy, high safety, and long lifespan, can be widely used in many fields with stringent requirements for energy storage device performance. In one application scenario, the capacitor of this invention can be used in rail transit vehicles, such as subways, light rail, and trams. These vehicles generate huge instantaneous power during braking, which traditional braking systems waste by converting into heat energy through friction. The capacitor of this invention, with its extremely high power density and fast response capability, can efficiently recover this braking energy, complete "charging" within seconds, and store the energy for the next start or acceleration of the vehicle, thereby significantly reducing the traction energy consumption of the vehicle. Its long cycle life can also well meet the high-intensity and long-term use requirements of rail transit vehicles.

[0053] In another application scenario, the capacitor of this invention can be used in the auxiliary power system of hybrid or pure electric vehicles. For example, in situations requiring instantaneous high power output, such as vehicle start-stop, rapid acceleration, or hill climbing, a power system consisting of the capacitor of this invention connected in parallel with the main battery can have the capacitor bear the main power surge, thereby protecting the main battery from high current surges and extending battery life. Simultaneously, the capacitor can quickly recover braking energy, improving the overall energy utilization efficiency of the vehicle. Its high safety features also meet the requirements of automotive-grade applications.

[0054] In another application scenario, the capacitor of this invention can be used for frequency regulation services in power systems. With the increasing proportion of intermittent energy sources such as wind and solar power in the power grid, the stability of the grid frequency faces significant challenges. The capacitor of this invention features millisecond-level power response speed and an ultra-long cycle life (capable of millions of deep charge-discharge cycles). It can serve as a highly efficient energy storage resource, rapidly responding to grid dispatch commands, absorbing energy when the frequency is high and releasing energy when the frequency is low, thereby achieving precise and rapid regulation of the grid frequency and ensuring the safe and stable operation of the power system.

Claims

1. A high-power titanium-based lithium-ion capacitor, comprising a positive electrode, a negative electrode, a separator, an electrolyte, and a sealed casing, characterized in that, The negative electrode sheet comprises a titanium-based negative electrode material coated with nano-carbon and modified by ion doping; The positive electrode sheet includes an activated carbon electrode material, wherein the activated carbon in the activated carbon electrode material has micropores and mesopores, and the volume ratio of the micropores to the mesopores is 3:1 to 5:

1. The positive electrode and the negative electrode have matching dynamic performance.

2. The high-power titanium-based lithium-ion capacitor according to claim 1, characterized in that, The titanium-based anode material is selected from one or more combinations of lithium titanate, titanium-based lithium vanadium oxide, fluorine-doped lithium titanate, and lithium titanate-based composite oxide.

3. The high-power titanium-based lithium-ion capacitor according to claim 1 or 2, characterized in that, The active grain size of the titanium-based anode material is 50-200 nm.

4. The high-power titanium-based lithium-ion capacitor according to claim 1, characterized in that, The compaction density of the negative electrode is 1.6-2.4 g / cm³, the compaction density of the positive electrode is 0.5-0.9 g / cm³, and the ratio of the compaction density of the negative electrode to the compaction density of the positive electrode is 1.8:1 to 4.8:

1.

5. The high-power titanium-based lithium-ion capacitor according to claim 1, characterized in that, The electrolyte is a lithium hexafluorophosphate electrolyte with a concentration of 1 mol / L, and its solvent is a carbonate solvent containing at least one of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate.

6. A method for preparing a high-power titanium-based lithium-ion capacitor, characterized in that, Includes the following steps: A negative electrode sheet is provided, the negative electrode sheet comprising a titanium-based negative electrode material coated with nano-carbon and modified by ion doping; A positive electrode is provided, the positive electrode comprising an activated carbon electrode material, wherein the activated carbon in the activated carbon electrode material has micropores and mesopores, and the volume ratio of the micropores to the mesopores is 3:1 to 5:1; Provide diaphragm and electrolyte; The negative electrode, the positive electrode, and the separator are assembled, injected with the electrolyte, and then encapsulated. The positive electrode and the negative electrode have matching dynamic performance, so that the capacitor retains no less than 92% of its capacity after 10,000 cycles at a 10C rate.

7. The preparation method according to claim 6, characterized in that, The step of providing the negative electrode sheet includes: mixing the titanium-based negative electrode material, conductive agent, and binder in a mass ratio of 90-92:3-5:3-6 to prepare a negative electrode slurry; then coating the negative electrode slurry onto a current collector and drying it to obtain the negative electrode sheet; and... The step of providing the positive electrode sheet includes: mixing the activated carbon, conductive agent, and binder in a mass ratio of 88-90:3-4:4-6 to prepare a positive electrode slurry, and then coating the positive electrode slurry onto the current collector and drying it to obtain the positive electrode sheet.

8. The preparation method according to claim 7, characterized in that, After drying, the process further includes a rolling step of rolling the negative electrode sheet and the positive electrode sheet to achieve a compaction density of 1.6-2.4 g / cm³ for the negative electrode sheet and 0.5-0.9 g / cm³ for the positive electrode sheet.

9. The preparation method according to claim 6, characterized in that, It also includes a step of aging and activation after the packaging, the aging and activation including: charging to 3.0V with a constant current of 0.2C, then disconnecting the circuit and letting it stand for 2 hours.

10. The preparation method according to claim 6, characterized in that, The encapsulation process is carried out under a vacuum pressure of -0.08 MPa to -0.1 MPa.

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