Bipolar current collector, bipolar pole piece, bipolar battery and manufacturing methods of bipolar current collector, bipolar pole piece and bipolar battery

Abstract

The invention provides a bipolar current collector, a bipolar pole piece and a bipolar battery, and the bipolar current collector can have improved conductivity, avoid permeation of bipolar metal, and have reduced mass density, thereby improving the energy density of the battery.

Description

Technical Field

[0001] This invention relates to the field of batteries, and more specifically to a bipolar current collector, a bipolar electrode including the bipolar current collector, and a bipolar battery, as well as methods for manufacturing them. Background Technology

[0002] Bipolar batteries are a novel battery structure, with the core being the use of bipolar electrodes. These bipolar electrodes are assembled in series within the battery, enabling both high voltage and high energy density to be achieved in the form of a single cell. This battery structure significantly improves the output voltage and energy density of the battery pack by reducing the use of components such as current collectors, packaging, and external electrical connections, while simultaneously reducing the battery's manufacturing cost.

[0003] The performance of bipolar electrodes largely depends on the characteristics of the bipolar current collector. An ideal bipolar current collector needs good conductivity, mechanical strength, and chemical stability, while also satisfying bipolar characteristics. Currently, conventional bipolar current collectors are typically prepared by repeatedly rolling copper and aluminum strips together. However, this method has significant limitations: during the repeated rolling process, the copper-aluminum composite foil undergoes penetration and mixing at the interface between the two metals, leading to a decrease in the performance of either the positive or negative electrode of the bipolar current collector. In particular, the negative electrode loses capacity due to the formation of lithium alloys, while the positive electrode suffers from metal leaching, resulting in deteriorated battery cycle performance. This, to some extent, limits the improvement of the overall battery energy density and the assurance of lifespan and performance.

[0004] In addition, if a polymer layer is added to form a traditional metal-polymer-metal "sandwich" structure, the presence of the polymer as a supporting structure will increase the overall thickness and mass of the bipolar current collector, further leading to a sacrifice and loss of the overall energy density of the battery.

[0005] Therefore, existing bipolar current collectors, whether produced through roll forming or polymer bonding, suffer from problems such as high interfacial impedance, weak interfacial bonding, poor long-term stability, and degradation of thermal stability and conductivity due to the polymer substrate. In particular, the interfaces of existing structures struggle to maintain absolute barrier effect against the penetration of active metal ions while achieving ultrathinness.

[0006] Therefore, developing novel bipolar current collector materials and more efficient preparation methods is of great significance for improving the performance and market competitiveness of bipolar batteries. Summary of the Invention

[0007] Technical issues

[0008] This invention is made to address the aforementioned problems in the prior art. The purpose of this invention is to provide a bipolar current collector, a bipolar electrode including the bipolar current collector, and a bipolar battery. The bipolar current collector can have a relatively thin overall thickness, which can be used to improve the conductivity of the bipolar electrode, prevent the penetration of bipolar metals, and simultaneously reduce the mass density of the bipolar current collector and the bipolar electrode, thereby increasing the energy density of the bipolar battery.

[0009] Technical solution

[0010] One aspect of the present invention is to provide a bipolar current collector, comprising:

[0011] First metal substrate layer;

[0012] An inorganic conductive isolation layer is coated or vapor-deposited onto one surface of the first metal substrate layer;

[0013] The second metal layer is coated or vapor-deposited on the surface of the inorganic conductive isolation layer away from the first metal substrate layer.

[0014] An active material with a first polarity can be supported on the surface of the first metal substrate layer that is far from the inorganic conductive isolation layer.

[0015] An active material with a second polarity can be supported on the surface of the second metal layer that is far from the inorganic conductive isolation layer.

[0016] In this invention, the first polarity and the second polarity correspond to the two polarities of the bipolar current collector, respectively, corresponding to the positive electrode or the negative electrode.

[0017] The first metal substrate layer may be a foil of a lightweight metal. Further, the first metal substrate layer may be an aluminum foil.

[0018] The second metal layer may be an iron-based metal plating layer, different from the first metal substrate layer. Further, the second metal layer may be a stainless steel plating layer.

[0019] Furthermore, the inorganic conductive isolation layer may be a carbon-containing conductive layer, which may be selected from at least one of conductive graphite, conductive carbon black, acetylene black, carbon nanotubes, or graphene; or, the inorganic conductive isolation layer may be a metallic conductive layer, which may be selected from at least one of copper powder, aluminum powder, nickel powder, silver powder, titanium powder, nickel-copper alloy powder, or aluminum-zirconium alloy powder.

[0020] Preferably, the inorganic conductive isolation layer is vacuum-deposited on the surface of the first metal substrate, and the second metal layer is vacuum-deposited on the surface of the inorganic conductive isolation layer away from the first metal substrate.

[0021] The thickness of the first metal substrate layer is 5–12 μm.

[0022] The thickness of the second metal layer is 1 to 5 μm, preferably 2.5 to 5 μm.

[0023] The thickness of the inorganic conductive isolation layer is 0.1–10 μm, preferably 2–4 μm.

[0024] Furthermore, a conductive carbon coating may be provided on the surface of the first metal substrate layer and / or the second metal layer away from the inorganic conductive isolation layer. The conductive carbon coating may be selected from at least one of conductive graphite, carbon black, carbon nanotubes or graphene, and its thickness is preferably 0.1 to 5 μm.

[0025] Another aspect of the present invention provides a method for preparing the bipolar current collector, comprising the following steps:

[0026] S1, Prepare the first metal substrate layer;

[0027] S2, an inorganic conductive paste is coated or vapor-deposited on one surface of the first metal substrate to obtain an inorganic conductive isolation layer;

[0028] S3, a second metal layer is coated or vapor-deposited on the surface of the inorganic conductive isolation layer away from the first metal substrate layer to obtain a bipolar current collector.

[0029] The inorganic conductive paste can be selected from at least one of conductive graphite paste, conductive carbon black paste, acetylene black paste, carbon nanotube paste, graphene paste, or metal powder paste.

[0030] Preferably, in step S2, an inorganic conductive paste is vacuum-deposited on one surface of the first metal substrate to obtain an inorganic conductive isolation layer; in step S3, a second metal layer is vacuum-deposited on the surface of the inorganic conductive isolation layer away from the first metal substrate to obtain a bipolar current collector.

[0031] Another aspect of the present invention provides a bipolar electrode sheet, comprising: the aforementioned bipolar current collector, and a positive electrode layer and a negative electrode layer respectively disposed on two surfaces of the bipolar current collector.

[0032] The material of the positive electrode layer can be selected from at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium cobalt oxide.

[0033] The material of the negative electrode layer can be selected from at least one of natural graphite, artificial graphite, silicon materials, soft carbon, and hard carbon.

[0034] Preferably, the positive electrode layer is coated on one surface of the bipolar current collector, and the negative electrode layer is coated on the other surface of the bipolar current collector.

[0035] Another aspect of the present invention provides a bipolar battery comprising the above-described bipolar electrode.

[0036] Beneficial effects

[0037] This invention provides a bipolar current collector, a bipolar electrode, and a bipolar battery. Unexpectedly, this invention discovers that by selecting a dense metal layer as a substrate and employing a specific sequence of "first depositing an inorganic separator layer, then depositing a second metal layer," a novel interface-enhanced current collector structure can be constructed.

[0038] This invention achieves atomic-level close contact between the inorganic isolation layer and the substrate by directly vacuum-depositing an inorganic isolation layer on a first metal substrate. This interface exhibits strong adhesion, low contact resistance, and is free of any organic contaminants, fundamentally solving the problems of interface instability and high impedance introduced by rolling or adhesives in existing technologies.

[0039] Furthermore, because the inorganic conductive separator is formed directly on a clean, dense metal surface, its film is dense and free of pinholes, effectively preventing the cross-interface penetration of any bipolar metal ions, thus avoiding internal short circuits and improving the battery's cycle life and safety. This is unparalleled by structures using polymers as intermediate layers, as polymers themselves may have microscopic free volumes and poor compatibility with metals.

[0040] Furthermore, the all-dry vapor deposition process of this invention avoids the use of polymer binders. This not only eliminates the negative impact of insulators on conductivity but also significantly reduces the overall mass density of the current collector. More importantly, this structure ensures smooth electron transport between the metal-inorganic layer-metal interface, achieving a balance between ultrathinness, lightweight design, and high conductivity.

[0041] The specific vapor deposition sequence of this invention ensures that the second metal layer grows on the already formed, flat and robust inorganic isolation layer, thereby obtaining a second metal layer with an ideal crystal structure and conductive pathway, which is of far superior quality to metal layers formed on rough or unstable polymer surfaces. Attached Figure Description

[0042] Figure 1 A schematic diagram of a bipolar current collector according to one embodiment of the present invention is shown.

[0043] Figure 2 A schematic diagram of a bipolar current collector according to one embodiment of the present invention is shown.

[0044] Figure 3 A schematic diagram of a bipolar electrode according to one embodiment of the present invention is shown.

[0045] Figure 4A schematic diagram of a bipolar electrode according to one embodiment of the present invention is shown.

[0046] Figure label:

[0047] 1: Bipolar current collector

[0048] 2: Bipolar electrode

[0049] 11: First metal substrate layer

[0050] 12: Inorganic conductive insulating layer

[0051] 13: Second metal layer

[0052] 14, 15: Conductive carbon coating

[0053] 16: Positive electrode layer

[0054] 17: Negative electrode layer Detailed Implementation

[0055] The present invention will be described in more detail below through embodiments. However, the following embodiments are provided to illustrate the invention, and it will be apparent to those skilled in the art that various modifications and changes can be made within the scope and concept of the invention, and the scope of the invention is not limited thereto.

[0056] In the following implementation schemes, "parts" refers to parts by weight. Unless otherwise specified, the materials used in the embodiments and comparative examples of the present invention are commercially available.

[0057] Example 1

[0058] 1. Preparation of bipolar current collectors

[0059] Aluminum foil with a thickness of 8 μm and a purity ≥99.9% (size: 300mm × 500mm, surface roughness Ra≤0.2μm) was used as the first metal substrate layer. The aluminum foil was ultrasonically cleaned with ethanol (300W power, 15min) and dried in a vacuum drying oven at 80℃ for 2h to remove surface oil and moisture. Using a vacuum evaporation machine, conductive graphite slurry (graphite powder purity 99.9%, particle size D50=1μm, mixed with anhydrous ethanol at a mass ratio of 1:1.5) was uniformly deposited onto one side of the aluminum foil at a evaporation rate of 5μm / h. After evaporation, the foil was transferred to a hot air drying oven at 120℃ and dried for 30min to form an inorganic conductive insulating layer with a thickness of 2μm (error ±0.1μm) (volume resistivity of the insulating layer after drying ≤5×10⁻³Ω・cm). Subsequently, on the surface of the isolation layer away from the aluminum foil, a vacuum evaporation machine was used with 316L stainless steel target material (purity 99.5%) as raw material. The evaporation temperature was controlled at 200℃ and the evaporation rate at 3μm / h to deposit a stainless steel layer with a thickness of 2μm (error ±0.1μm). The adhesion of the stainless steel layer after deposition was ≥5N / 25mm, tested according to GB / T5210-2006. Finally, a bipolar current collector with a size of 300mm×500mm was obtained (the aluminum foil layer is the positive electrode side substrate, and the stainless steel coating is the negative electrode side).

[0060] 2. Preparation of bipolar electrodes

[0061] 1) Preparation of positive electrode slurry. The raw materials were weighed according to the mass ratio of lithium iron phosphate (LiFePO4, purchased from Sumitomo Chemical SP-01, D50=5±0.5μm): conductive carbon black (Ketjen Black EC-600JD): PVDF binder (Arkema Kynar761) = 90:5:5. First, lithium iron phosphate and conductive carbon black were added to N-methylpyrrolidone (NMP, purity 99.5%) and dispersed in a high-speed disperser (3000 r / min) for 30 min to form a premixed liquid. Then, PVDF binder (PVDF was first dissolved in NMP to prepare a 10% mass fraction adhesive solution) was added and transferred to a planetary mixer (1500 r / min, vacuum degree -0.09 MPa) and stirred for 2 h. The amount of NMP was adjusted so that the solid content of the slurry was controlled at 65±2%, and finally a positive electrode slurry with a viscosity of 3000±500 mPa・s (25℃, measured by Brookfield DV-II+Pro viscometer) was obtained.

[0062] 2) Preparation of negative electrode slurry. Weigh the raw materials according to the mass ratio of artificial graphite (BTR S360, D50=15μm): conductive carbon black (Ketjen Black EC-600JD): CMC (sodium carboxymethyl cellulose, Asahi Kasei AA-10): styrene-butadiene rubber (SBR, Japan ZEON4113) = 85:10:2:3. First, add the artificial graphite and conductive carbon black to deionized water and disperse for 20 min in a high-speed disperser (2500 r / min). Then, add the CMC aqueous solution (CMC dissolved in deionized water to prepare a 2% mass fraction solution) and the SBR emulsion (40% solid content) sequentially. Stir in a planetary mixer (1200 r / min) for 1.5 h, adjusting the amount of deionized water to control the solid content of the slurry at 50±2%, finally obtaining a negative electrode slurry with a viscosity of 4000±500 mPa・s (25℃).

[0063] 3) Coating and Drying. A slit coater (model: MTI-SC-300) was used to uniformly coat the negative electrode slurry onto the stainless steel layer of the bipolar current collector (coating speed 3 m / min, wet film thickness 100 μm). Immediately after coating, the material was transferred to a segmented drying tunnel (segment 60℃, segment 80℃, segment 110℃, total drying time 15 min). After drying, the dry film thickness of the negative electrode layer was 25 ± 2 μm. Using the same equipment, the positive electrode slurry was coated onto the aluminum foil layer of the current collector (coating speed 2.5 m / min, wet film thickness 120 μm). After the same segmented drying process, the dry film thickness of the positive electrode layer was 30 ± 2 μm. After drying, the electrode sheets were cooled to room temperature in a drying room at 25℃ and relative humidity ≤30% for later use.

[0064] 4) Rolling and Cutting. The dried electrode sheets are placed in a two-roll press, and the rolling pressure is controlled at 12MPa and the rolling speed is 1m / min. The positive and negative electrode layers are rolled once. After rolling, the electrode density is measured: the density of the positive electrode layer is ≥2.3g / cm³, and the density of the negative electrode layer is ≥1.6g / cm³. The rolled electrode sheets are cut into square bipolar electrode sheets with a size of 50mm×50mm using a fully automatic electrode sheet cutting machine (model: JCD-300) (each electrode sheet has a 5mm×50mm tab area reserved, and the tab area is not coated with slurry). After cutting, the edges of the electrode sheets are free of burrs (burr length ≤50μm).

[0065] 3. Preparation of Lithium-ion Batteries

[0066] 1) Cell Stacking. A PP / PE / PP composite separator (model: Celgard2325, thickness 25μm, air permeability 120s / 100mL) is used, cut into 52mm×52mm square separators. In a dry room at 25℃ and relative humidity ≤10%, a manual stacking machine is used to stack the cells in the order of "bipolar electrode sheet → separator → bipolar electrode sheet" (the positive and negative electrode surfaces of adjacent electrode sheets face each other, the separator completely covers the active area of ​​the electrode sheet, and the edge alignment error ≤0.5mm), stacking a total of 5 bipolar electrode sheets.

[0067] Four layers of separators form a stacked battery cell (overall cell size: 52mm×52mm×3mm).

[0068] 2) Cell Packaging. Aluminum-plastic film (model: DNP-880, thickness: 120μm, structure: PA / Al / PP) was used and cut into 100mm×100mm square sheets. The stacked cells were placed in the aluminum-plastic film and three-sided sealing was performed using a vacuum heat sealer (model: MTI-HS-200) (heat sealing temperature 180℃, heat sealing pressure 0.5MPa, heat sealing time 3s), leaving one side as a liquid injection port. After packaging, the cells were transferred to a vacuum baking oven and baked at 80℃ and a vacuum degree of -0.095MPa for 12 hours to remove internal moisture (moisture content of the cells after baking ≤20ppm, measured by the Karl Fischer method).

[0069] 3) Electrolyte injection and sealing. An electrolyte solution (composition: 1 mol / L LiPF6 dissolved in EC / DMC / EMC (volume ratio 1:1:1), with 2% Vinylene Carbonate (VC) added as a film-forming agent) was used. In a drying chamber, the electrolyte was injected at a rate of 0.18 mL / Ah (cell design capacity 100 mAh, injection volume 18 μL) through the injection port. After injection, the solution was allowed to stand for 30 minutes to allow the electrolyte to fully wet the separator and electrode plates. The injection port was then sealed using a vacuum heat sealer (heat sealing parameters as before), completing the fabrication of the soft-pack lithium-ion battery (battery model: 100 mAh soft-pack bipolar battery, dimensions: 100 mm × 100 mm × 3.5 mm).

[0070] 4) Formation and Aging. The packaged batteries are placed in a battery formation cabinet (model: NewareCT-4008) and the formation process is performed as follows: constant current charging at 0.1C to 3.65V (cutoff current 0.01C), standing for 5 minutes, constant current discharging at 0.1C to 2.5V (cutoff current 0.01C) to complete the formation. After formation, the batteries are aged at 25℃ for 72 hours. Qualified batteries without leakage or bulging are selected for subsequent battery performance testing (such as cycle life, rate performance, high and low temperature performance, etc.).

[0071] Example 2

[0072] Except for the preparation of the bipolar current collector, in which carbon nanotube slurry (multi-walled carbon nanotubes with a purity of 99.5%, an outer diameter of 8-15 nm, a length of 0.8-2 μm, and mixed with anhydrous ethanol at a mass ratio of 1:2.5-3) is vacuum-deposited on the surface of aluminum foil to form an inorganic conductive isolation layer with a thickness of 2 μm after drying, the bipolar current collector, bipolar electrode and lithium-ion battery are prepared in the same manner as in Example 1.

[0073] Example 3

[0074] Except for the preparation of the bipolar current collector, in which a nickel powder slurry (nickel powder purity 99.8%, particle size D50 = 1-3 μm, mixed with anhydrous ethanol at a mass ratio of 1:1.8-2.2) is vacuum-deposited on the surface of the aluminum foil to form an inorganic conductive isolation layer with a thickness of 2 μm after drying, the bipolar current collector, bipolar electrode and lithium-ion battery are prepared in the same manner as in Example 1.

[0075] Comparative Example 1

[0076] A bipolar current collector was prepared by repeatedly rolling and laminating commercially available copper-aluminum composite foil, without an intermediate separator layer. The preparation processes for the remaining bipolar electrodes and lithium-ion batteries were the same as in Example 1.

[0077] Comparative Example 2

[0078] A 5 μm thick polyimide (PI) film doped with carbon nanotube conductive material was used as a support layer and placed between aluminum foil and copper foil. The resulting bipolar current collector with a "sandwich" structure was then bonded together. The fabrication processes for the remaining bipolar electrodes and lithium-ion battery were the same as in Example 1.

[0079] Test case

[0080] 1. Surface resistance measurement

[0081] The surface resistivity of the current collector was measured using the four-probe method to evaluate its conductivity.

[0082] 1.1 Measurement Basis

[0083] Referring to the relevant provisions of the four-probe method in GB / T15519-2017 "Test Method for Resistivity and Minority Carrier Lifetime of Silicon Single Crystal", the measurement parameters were adjusted in combination with the characteristics of the current collector metal foil.

[0084] 1.2 Sample Preparation

[0085] Square samples of 50mm × 50mm were cut from the current collectors of each embodiment and comparative example along different directions (longitudinal and transverse). Three parallel samples were prepared for each group of samples. The sample surface was wiped with anhydrous ethanol cotton balls to remove oil and dust. The samples were then left to stand for 30 minutes in an environment of 25℃±2℃ and relative humidity≤30% to avoid surface adsorption of water vapor affecting the measurement.

[0086] 1.3 Measuring Instruments

[0087] Four-probe measuring instrument: Model RTS-8 dual electrical four-probe measuring instrument (resolution 0.001Ω, test range 10⁻) 4 ~10 6 Ω); Sample stage: with horizontal adjustment function to ensure full contact between sample and probe.

[0088] 1.4 Measurement Conditions

[0089] Test environment: Temperature 25℃±2℃, relative humidity ≤30%, no electromagnetic interference;

[0090] Probe parameters: probe spacing 1mm, probe pressure 50g±5g (avoid excessive pressure that could damage the sample or insufficient pressure that could lead to poor contact);

[0091] Test current: Selected according to the conductivity of the current collector. 100mA constant current was selected for Examples 1 to 3 and Comparative Example 1 (aluminum / stainless steel layer), and 10mA constant current was selected for Comparative Example 2 (including PI layer) to avoid excessive current causing the sample to heat up.

[0092] 1.5 Measurement Procedure

[0093] Place the sample flat on the sample stage and adjust it to be level so that the four probes are perpendicularly pressed against the sample surface (avoiding the 10mm edge area to prevent edge effects); start the measuring instrument and record the current resistance value. Select 5 measurement points for each sample (1 point in the center + 1 point at each of the four corners); calculate the surface resistance R according to the formula. s =0.7854×R (where R is the resistance value displayed by the measuring instrument, and 0.7854 is the correction factor for the four probes on an infinitely large sample); calculate the average surface resistance of 5 measurement points for each parallel sample, and take the average value of 3 parallel samples as the final surface resistance value of the group of samples.

[0094] 1.6 Data Judgment

[0095] Conductivity performance: The smaller the surface resistance, the better the conductivity; compare the surface resistance differences between the examples and the comparative examples to evaluate the conductivity performance.

[0096] 2. Interface penetration observation

[0097] The samples were subjected to thermal cycling treatment (-20°C to 60°C, 200 times), and the cross-section of the current collector was analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). After thermal cycling, the metal diffusion was confirmed by SEM and EDS.

[0098] 2.1 Measurement Basis

[0099] Referring to the cold and hot cycling pretreatment requirements in GB / T30767-2014 "Electrochemical Test Methods for Corrosion of Metals and Alloys", and combining the SEM / EDS microscopic analysis method.

[0100] 2.2 Sample Preparation

[0101] From the current collectors of each embodiment and comparative example, cut strips of 10mm × 20mm, with 3 parallel samples per group; cut the samples along the thickness direction with a diamond cutting tool to obtain a fresh cross section (avoiding compression deformation), then polish the cross section with 1500#, 3000#, and 5000# sandpaper in sequence, and finally polish it to a mirror finish with 0.5μm alumina polishing liquid, ultrasonically clean (ethanol, 300W, 5min), and then dry.

[0102] 2.3 Measuring Instruments

[0103] Hot and cold cycling chamber: Model ESPECSH-241 (temperature range -40℃~150℃, temperature control accuracy ±1℃); Scanning electron microscope (SEM): Model ZEISSSigma300 (accelerating voltage 5~20kV, resolution 0.8nm); Energy dispersive spectroscopy (EDS): Model OxfordX-MaxN50 (elemental detection range B~U, resolution 127eV).

[0104] 2.4 Measurement Conditions

[0105] 2.4.1 Pretreatment for hot and cold cycles

[0106] Cycling range: -20℃~60℃; Cycling rate: heating rate 5℃ / min, cooling rate 5℃ / min; Isothermal time: 60℃ isothermal for 30min, -20℃ isothermal for 30min (total duration of 1 cycle ≈ 48min); Number of cycles: 200 times. During the cycle, the sample is not clamped by external force to avoid deformation.

[0107] 2.4.2 SEM Observation

[0108] Sample fixation: Fix the sample cross-section upwards onto the conductive adhesive and perform gold sputtering; Observation parameters: Accelerating voltage 15kV, working distance 8mm, magnification ×5000 (focusing on the interlayer interface area); Observation positions: Select 3 areas each at the center, left edge, and right edge of the cross-section of each sample and record whether there is peeling, cracking, or diffusion layer formation at the interface.

[0109] 2.4.3 EDS Analysis

[0110] Line scan: A scan path is set along the vertical direction of the cross section (from the first metal substrate layer to the second metal layer), with a step size of 0.1 μm. The scan length covers the total thickness of the current collector, and the signal intensity changes of key elements (Al, Fe, C, Ni, Cu, etc.) are recorded. Surface scan: An interface region (area 10 μm × 5 μm) is selected for surface scan to obtain the element distribution spectrum. Data analysis: The thickness of the diffusion layer is determined by the "signal crossover width" of the line scan curve, and whether elements have penetrated across layers is determined by the surface scan spectrum.

[0111] 2.5 Data Judgment

[0112] Structural stability: The smaller the diffusion layer thickness and the less peeling / cracking at the interface, the better the structural stability; compare the diffusion degree of the embodiment (containing an inorganic conductive isolation layer) and the comparative example (without an inorganic conductive isolation layer, or containing a polymer isolation layer) to evaluate the anti-permeability effect of different structure current collectors.

[0113] 3. Mass density and energy density assessment

[0114] The mass per unit area of ​​different samples is measured and the mass density is calculated to reflect the degree of lightweighting and the energy storage efficiency per unit mass.

[0115] 3.1 Measurement Basis

[0116] Referencing the mass density test method in GB / T29062-2012 "Metal Foil for Lithium-ion Batteries" and the energy density calculation method in GB / T31484-2015 "Cycle Life Requirements and Test Methods for Power Batteries for Electric Vehicles", the method was combined with the energy density calculation method in GB / T31484-2015 "Cycle Life Requirements and Test Methods for Power Batteries for Electric Vehicles".

[0117] 3.2 Sample Preparation

[0118] 3.2.1 Measurement of mass density of current collector

[0119] From the current collectors of each embodiment / comparative example, cut out 100mm×100mm square samples (no slurry coating, only the current collector body), with 3 parallel samples in each group; use a micrometer (accuracy 0.001mm) to measure the thickness at 9 points (3×3 grid) on the sample, and calculate the average thickness d (unit: mm).

[0120] 3.2.2 Battery Energy Density Measurement

[0121] Samples were selected from qualified batteries in each example / comparative example that showed no leakage or bulging after formation and aging, with 3 parallel samples in each group; the batteries were placed in an environment of 25℃±2℃ for 24 hours before measurement to ensure that the battery condition was stable.

[0122] 3.3 Measuring Instruments

[0123] Precision electronic balance: Model Mettler Toledo ME204E (accuracy 0.1mg, measuring range 220g); Micrometer: Model Mitutoyo 293-340 (accuracy 0.001mm); Battery testing system: Model Neware CT-4008 (current accuracy ±0.1%FS, voltage accuracy ±0.05%FS).

[0124] 3.4 Measurement Conditions

[0125] Mass density measurement environment: 25℃±2℃, relative humidity ≤30%; Energy density measurement environment: 25℃±2℃, no airflow interference.

[0126] 3.5 Measurement Procedure

[0127] 3.5.1 Calculation of the mass density of the current collector

[0128] Weigh the sample mass m (unit: kg) using a precision electronic balance; calculate the sample volume V = 0.1m × 0.1m × d (unit: m³, where 0.1m is the sample side length and d is the sample thickness); the mass density ρ = m / V (unit: kg / m³), and the average value of the three parallel samples is taken as the final mass density.

[0129] 3.5.2 Calculation of Battery Energy Density

[0130] Baseline capacity test: Charge at a constant current of 0.2C to 3.65V (cutoff current 0.01C), let stand for 5 minutes, then discharge at a constant current of 0.2C to 2.5V, and record the discharge capacity C0 (unit: Ah, i.e., rated capacity); Average discharge voltage test: Repeat the above charge and discharge process, record the discharge curve, and divide the "voltage-capacity integral value" of the discharge curve by the discharge capacity to obtain the average discharge voltage U. avg (Unit: V); Battery energy calculation: Rated energy E = C0 × U avg (Unit: Wh); Total battery mass weighing: Weigh the total battery mass M (unit: kg, including aluminum-plastic film, electrolyte, and battery cell) using a precision electronic balance; Mass energy density E m =E / M (unit: Wh / kg), the average of 3 parallel samples is used as the final mass energy density.

[0131] 3.6 Data Judgment

[0132] Lightweight effect: The lower the current collector mass density, the better the lightweight effect; compare the mass density difference between the example (aluminum-based + inorganic conductive separator + thin stainless steel layer) and the comparative example (copper-aluminum composite foil or sandwich structure); Energy storage efficiency: The higher the battery mass energy density, the better the energy storage efficiency; combine the lightweight effect to evaluate the effect of current collector structure on improving battery energy density.

[0133] 4. Rate performance (5C discharge capacity retention) and cycle life (500-cycle capacity retention) testing

[0134] 4.1 Test Basis

[0135] Refer to the relevant provisions of GB / T31484-2015 "Cycle Life Requirements and Test Methods for Power Batteries for Electric Vehicles" and GB / T31485-2015 "Safety Requirements and Test Methods for Power Batteries for Electric Vehicles".

[0136] 4.2 Sample Preparation

[0137] Qualified batteries that showed "no leakage or bulging after formation and aging" from each example / comparative example were selected, with 3 parallel samples in each group; the batteries were left to stand for 24 hours in an environment of 25℃±2℃ before testing, and the initial state of the batteries (appearance, voltage) was recorded.

[0138] 4.3 Testing Instruments

[0139] Battery testing system: Model NewareCT-4008 (supports constant current charging and discharging, current range 0.01C~10C); Temperature chamber: Model BinderMK53 (temperature control accuracy ±0.5℃, temperature range 0℃~80℃).

[0140] 4.4 Test Conditions

[0141] Test environment: constant temperature 25℃±2℃, relative humidity ≤60%; charge and discharge cut-off conditions: charging cut-off voltage 3.65V (after constant current charging to 3.65V, there is no constant voltage stage), discharging cut-off voltage 2.5V; resting time: rest for 5 minutes after each charge and discharge to avoid battery overheating affecting the test.

[0142] 4.5 Test Procedure

[0143] 4.5.1 Rate Performance Test (5C Discharge Capacity Retention Rate)

[0144] Reference capacity calibration: Charge to 3.65V at a constant current of 0.2C (cutoff current 0.01C), let stand for 5 minutes, then discharge to 2.5V at a constant current of 0.2C, and record the discharge capacity C. 0.2C(As a baseline capacity); 5C discharge test: Charge at a constant current of 0.5C to 3.65V (cutoff current 0.01C), let stand for 5 minutes, then discharge at a constant current of 5C to 2.5V, and record the discharge capacity C. 5C Capacity retention rate calculation: 5C discharge capacity retention rate η1 = (C 5C / C 0.2C The final result is calculated as () × 100%, with the average of the three parallel samples as the final value.

[0145] 4.5.2 Cycle life test (capacity retention after 500 cycles)

[0146] Initial capacity recording: Repeat the baseline capacity calibration steps in the "Rate Performance Test" and record the initial discharge capacity C. initial Cyclic regime: Adopts a "0.5C charging - 0.5C discharging" cycle, the specific process is as follows:

[0147] ① Charge at a constant current of 0.5C to 3.65V (cutoff current 0.01C), and let stand for 5 minutes;

[0148] ② Discharge at a constant current of 0.5C to 2.5V, and let stand for 5 minutes;

[0149] ③ After every 100 cycles, pause the test, perform one charge-discharge cycle at 0.2C, and record the current discharge capacity C. n (n is the number of cycles); 500-cycle capacity retention rate calculation: 500-cycle capacity retention rate η2 = (C 500 / C initial ×100% (If the capacity decays to below 80% of the initial capacity during cycling, terminate the test early, but record the number of weeks to terminate); Post-cycle status check: After 500 cycles, observe the appearance of the battery for bulging or leakage, and use SEM to observe whether the electrode sheets have detached.

[0150] 4.6 Data Judgment

[0151] Rate performance: The higher the 5C discharge capacity retention rate, the better the rate performance; Cycle life: The higher the 500-cycle capacity retention rate, the better the cycle stability; Compare the electrochemical performance differences between the examples and the comparative examples to evaluate the effect of the bipolar current collector structure on battery performance improvement.

[0152] [Table 1]

[0153]

[0154] Experimental conclusions

[0155] As can be seen from the table above, in the surface resistance test, the surface resistance of the current collectors prepared in Examples 1 to 3 is all below 8 Ω / □, which is significantly better than that of Comparative Examples 1 to 2 (19.2 to 20.5 Ω / □). This proves that the current collector prepared by the preparation method of the present invention, which combines a specific metal substrate layer, an inorganic conductive isolation layer and a vapor-deposited metal layer, can significantly improve the electron transport efficiency.

[0156] In the interfacial penetration observation test, after thermal shock, no metal interpenetration was observed in the current collectors of Examples 1-3. The inorganic conductive insulating layer maintained a complete and tight interface with the aluminum foil and stainless steel layer, with no gaps or interlayer migration of elements, no peeling or diffusion layer formation, and a stable conductive path in the inorganic conductive insulating layer. Conversely, the current collector of Comparative Example 1 exhibited significant Cu-Al interfacial interdiffusion, and metal penetration led to an unstable interface structure, easily causing electrochemical failure. Although there was no significant metal penetration between the support layer and the aluminum foil / copper foil interface of the current collector of Comparative Example 2, the polymer layer, acting as an insulator, negatively impacted conductivity, resulting in increased sheet resistance and a significant reduction in battery energy density.

[0157] Furthermore, the current collectors in Examples 1-3 have significantly lower unit area mass and mass density than those in Comparative Examples 1-2, directly contributing to improved energy density. The batteries prepared using the current collectors from Examples 1-3 all have energy densities exceeding 180 Wh / kg, and their rate performance at 5C discharge maintains over 80% of its capacity, significantly better than Comparative Examples 1-2.

[0158] Furthermore, the batteries prepared using the current collectors of Examples 1-3 retain approximately 90% of their capacity after 500 cycles, which is more than 10% higher than that of the comparative examples, demonstrating superior long-term stability.

[0159] The bipolar current collector of this invention innovatively uses a first metal as a substrate layer, on which an inorganic conductive isolation layer and a second metal layer are deposited by vapor deposition, which can stably realize the manufacturing of ultra-thin structures while ensuring excellent conductivity.

[0160] In summary, the bipolar current collector structure of this invention, through the rational design of the combination of metal and conductive insulating materials, achieves improved conductivity, enhanced structural stability, lightweight control, and optimized overall battery performance, demonstrating significant technical advantages and industrialization value in bipolar battery applications.

Claims

1. A bipolar current collector, characterized in that, include: First metal substrate layer; An inorganic conductive isolation layer is coated or vapor-deposited onto one surface of the first metal substrate layer; The second metal layer is coated or vapor-deposited on the surface of the inorganic conductive isolation layer away from the first metal substrate layer.

2. The bipolar current collector according to claim 1, characterized in that, The first metal substrate is a foil of lightweight metal.

3. The bipolar current collector according to claim 2, characterized in that, The first metal substrate layer is aluminum foil.

4. The bipolar current collector according to claim 1, characterized in that, The second metal layer is an iron-based metal plating layer that is different from the first metal substrate layer.

5. The bipolar current collector according to claim 4, characterized in that, The second metal layer is a stainless steel plating.

6. The bipolar current collector according to claim 1, characterized in that, The inorganic conductive isolation layer is a carbon-containing conductive layer or a metal conductive layer.

7. The bipolar current collector according to claim 6, characterized in that, The carbon-containing conductive layer is selected from at least one of conductive graphite, conductive carbon black, acetylene black, carbon nanotubes, or graphene.

8. The bipolar current collector according to claim 6, characterized in that, The conductive metal layer is selected from at least one of copper powder, aluminum powder, nickel powder, silver powder, titanium powder, nickel-copper alloy powder, or aluminum-zirconium alloy powder.

9. The bipolar current collector according to claim 1, characterized in that, The inorganic conductive isolation layer is vacuum-deposited on the surface of the first metal substrate, and the second metal layer is vacuum-deposited on the surface of the inorganic conductive isolation layer away from the first metal substrate.

10. The bipolar current collector according to claim 1, characterized in that, The thickness of the first metal substrate layer is 5–12 μm, the thickness of the second metal layer is 1–5 μm, and the thickness of the inorganic conductive isolation layer is 2–4 μm.

11. The bipolar current collector according to claim 1, characterized in that, A conductive carbon coating is provided on the surface of the first metal substrate layer and / or the second metal layer away from the inorganic conductive isolation layer, wherein the conductive carbon coating is selected from at least one of conductive graphite, carbon black, carbon nanotubes or graphene.

12. A method for preparing the bipolar current collector according to claim 1, characterized in that, Includes the following steps: S1, Prepare the first metal substrate layer; S2, an inorganic conductive paste is coated or vapor-deposited on one surface of the first metal substrate to obtain an inorganic conductive isolation layer. S3, a second metal layer is coated or vapor-deposited on the surface of the inorganic conductive isolation layer away from the first metal substrate layer to obtain a bipolar current collector.

13. The method for preparing a bipolar current collector according to claim 12, characterized in that, The inorganic conductive paste is selected from at least one of conductive graphite paste, conductive carbon black paste, acetylene black paste, carbon nanotube paste, graphene paste, or metal powder paste.

14. A bipolar electrode, characterized in that, include: The bipolar current collector as described in claim 1; And positive and negative electrode layers respectively disposed on the two surfaces of the bipolar current collector.

15. A bipolar battery, characterized in that, Includes the bipolar electrode as described in claim 14.

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