Battery cell, battery pack and electric equipment

Abstract

The invention relates to the technical field of batteries, in particular to a battery cell, a battery and electric equipment. The battery cell comprises a buffer structure which is located between a positive plate and a diaphragm, and / or the buffer structure is located between a negative plate and the diaphragm; the shape memory member has a first shape and a second shape, the length of the second shape being greater than the length of the first shape. The buffer structure in the second shape is arranged between the positive plate and the negative plate of the battery cell, and the buffer structure adjusts the expansion stress of the pole piece through self stretching, so that the pole piece does not excessively expand to extrude the battery shell during cyclic charging and discharging, the risk of damage to the battery shell is reduced, and the cycle life of the battery is prolonged.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a battery cell, a battery pack, and an electrical device. Background Technology

[0002] To improve the energy density of a battery cell, the thickness of the cell casing is typically optimized. However, during charging and discharging, factors such as the deintercalation of active materials in the electrodes, the growth of the solid electrolyte interface (SEI) film, and gas evolution can cause a sharp increase in the expansion pressure of the electrode sheets. This pressure can then compress the cell casing, leading to a significant decrease in the impact and compression resistance of the cell casing, and in some cases, even rupture, resulting in an accident. Summary of the Invention

[0003] This application provides a battery cell, a battery pack, and an electrical device to solve the safety problem caused by the battery cell casing cracking due to a decrease in its impact and compression resistance.

[0004] One embodiment provides a battery cell, which includes a housing and an electrode assembly. The housing covers the electrode assembly, and the electrode assembly includes an electrode sheet and a separator. The electrode sheet includes a positive electrode sheet and a negative electrode sheet, and the separator is located between the positive electrode sheet and the negative electrode sheet. The battery cell also includes a buffer structure located between the positive electrode sheet and the separator, and / or, the buffer structure is located between the negative electrode sheet and the separator. The electrode assembly has a first direction, and the housing has a first wall located at one end of the electrode assembly along the first direction. The buffer structure includes a shape memory element extending along the first direction and having a first end facing the first wall, the first end being connected to the first wall. The shape memory element has a first shape and a second shape, the length L3 of the second shape being greater than the length L1 of the first shape. The length L3 of the first shape is obtained by testing the shape memory element at a temperature of 50℃-60℃, and the length L1 of the first shape is obtained by testing the shape memory element at a temperature of 25℃-35℃.

[0005] In one embodiment, under the second shape, the pre-stretch strain of the shape memory element is 3% to 5%.

[0006] In one embodiment, an insulating element is connected between the first end and the first wall; and / or, the housing has a second wall located at the other end of the pole group along a first direction, the shape memory element has a second end facing the second wall, the second end being connected to the second wall; an insulating element is connected between the second end and the second wall.

[0007] In one embodiment, the diameter d of the shape memory device satisfies 80μm≤d<200μm.

[0008] In one embodiment, there are multiple shape memory elements, and the multiple shape memory elements are arranged at intervals.

[0009] In one embodiment, the shape memory element includes a shape memory alloy wire.

[0010] In one embodiment, the electrode includes a current collector and an active material layer disposed on the surface of the current collector. The electrode has an edge along a first direction, and the parallelism between the shape memory device and the edge of the electrode is 0~0.5mm; and / or, the electrode includes a current collector and an active material layer disposed on the surface of the current collector. In the first direction, the length L1 of the first shape of the shape memory device is greater than the width L2 of the active material layer, satisfying: L2=α×L1, where the value of α ranges from 80% to 95%.

[0011] In one embodiment, the material of the shape memory device includes at least one of Ni-Ti based alloy, Cu based alloy, and Fe based alloy.

[0012] In one embodiment, the Ni-Ti based alloy includes a Ni-Ti alloy, a Ni-Ti-Cu alloy, or a Ni-Ti-Hf alloy; and / or, the Cu-based alloy includes a Cu-Al-Ni alloy; and / or, the Fe-based alloy includes an Fe-Mn-Si alloy.

[0013] In one embodiment, the buffer structure further includes a buffer layer located between the electrode and the diaphragm, and a shape memory element disposed on the side surface of the buffer layer facing the electrode and / or the diaphragm; or, the shape memory element is disposed in the buffer layer and covered by the buffer layer.

[0014] In one embodiment, the thickness of the buffer layer is greater than the diameter of the shape memory device, and the thickness h of the buffer layer satisfies 80μm < h ≤ 200μm; and / or, the porosity of the buffer layer is 20%~30%.

[0015] In one embodiment, the buffer layer is an insulating adhesive layer; or, the surface of the shape memory element is provided with an insulating layer, and the buffer layer includes an adhesive and a conductive agent.

[0016] One embodiment also provides a battery pack including the aforementioned battery cells.

[0017] One embodiment also provides an electrical device, which includes the battery pack described above, and the battery pack serves as the power supply for the electrical device.

[0018] This application utilizes a shape memory element with a second shape, positioned between the positive and negative electrodes of a battery cell. Leveraging its phase change / pseudoelastic expansion characteristics, this element generates a reverse constraint force when the electrodes expand during charging and discharging, significantly reducing the electrode expansion rate. This constraint force effectively disperses the compressive force exerted by the electrodes on the casing, preventing deformation or increased internal pressure on the casing and ultimately reducing the risk of casing rupture. Understandably, when the battery cell is not charging or discharging, the shape memory element is in its second shape, with a length of L3. During charging and discharging, the battery cell generates heat, causing its temperature to rise. As the temperature increases, the shape memory element transforms from its second shape to its first shape, with a length of L1. Since L1 < L3, the shape memory element contracts after the battery cell heats up, creating space that helps provide expansion space for the electrodes during charging and discharging, reducing the pressure exerted by the expanding electrodes on the casing. Attached Figure Description

[0019] Figure 1 This is a side view of a battery cell in one embodiment; Figure 2 This is a front view of the battery cell in one embodiment; Reference numerals: 101-positive electrode, 102-negative electrode, 103-separator, 104-shape memory alloy wire, 105-buffer layer, 201-tab, 202-insulator. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings. Similar elements in different embodiments are referred to by associated similar element reference numerals. In the following embodiments, many details are described to facilitate a better understanding of this application. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other elements, materials, or methods. In some cases, certain operations related to this application are not shown or described in the specification. This is to avoid obscuring the core parts of this application with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; they can fully understand the related operations based on the description in the specification and general technical knowledge in the art.

[0021] Furthermore, the features, operations, or characteristics described in the specification can be combined in any suitable manner to form various embodiments. At the same time, the steps or actions in the method description can be rearranged or adjusted in a manner obvious to those skilled in the art. Therefore, the various orders in the specification and drawings are only for the clear description of a particular embodiment and do not imply a necessary order, unless otherwise stated that a particular order must be followed.

[0022] The serial numbers assigned to components in this document, such as "first" and "second," are used only to distinguish the described objects and have no sequential or technical meaning. The terms "connection" and "linkage" used in this application, unless otherwise specified, include both direct and indirect connections (linkages).

[0023] This embodiment provides a battery cell, such as Figure 1 and Figure 2 As shown. The battery cell includes a housing and an electrode assembly. The housing covers the electrode assembly, which includes electrode plates and a separator 103. The electrode plates include a positive electrode plate 101 and a negative electrode plate 102. The separator 103 is located between the positive electrode plate 101 and the negative electrode plate 102. The battery cell also includes a buffer structure located between the positive electrode plate 101 and the separator 103, and / or, the buffer structure is located between the negative electrode plate 102 and the separator 103. The electrode assembly has a first direction, and the housing has a first wall located at one end of the electrode assembly along the first direction. The buffer structure includes a shape memory element extending along the first direction. The shape memory element has a first end facing the first wall, and the first end is connected to the first wall. The shape memory element has a first shape and a second shape. The length L3 of the second shape is greater than the length L1 of the first shape. The length L3 of the first shape is obtained by testing the shape memory element at a temperature of 50℃-60℃, and the length L1 of the first shape is obtained by testing the shape memory element at a temperature of 25℃-35℃.

[0024] Understandably, when the battery cell is not charging or discharging, the shape memory element within it is in a second shape with a length of L3. During charging and discharging, the cell generates heat, causing its temperature to rise. As the temperature increases, the shape memory element transforms from the second shape to a first shape with a length of L1. Since L1 < L3, the shape memory element contracts and creates space after the cell heats up. This provides expansion space for the expanding electrodes during charging and discharging, reducing the pressure of the expanding electrodes on the casing. In other words, by placing a second-shaped shape memory element between the positive and negative electrodes, this element adjusts the expansion stress of the electrodes through its own expansion and contraction, preventing the electrodes from excessively expanding and compressing the casing during cyclic charging and discharging, thus reducing the risk of casing breakage.

[0025] It is understandable that shape memory devices have a first shape and a second shape. The first shape is the shape of the shape memory device when its temperature rises above the high-temperature phase memory temperature, and the second shape is the shape of the shape memory device when its temperature drops below the low-temperature phase memory temperature. The lengths L1 and L3 of the shape memory device are measured as follows: the battery cell is discharged to 0% SOC, then left to stand for 24 hours to balance the internal pressure. Next, the shape memory device is disassembled and removed, then left to stand for 1 hour to eliminate residual stress. Then, the shape memory device is heated to 60°C and held for 1 hour. Its length is then measured using a digital caliper or laser length measuring instrument and recorded as L1 (measured at high temperature). Finally, the heated shape memory device is cooled to 25°C, held for 1 hour, and its length is measured again and recorded as L3.

[0026] In one embodiment, the housing has a first wall located at one end of the electrode assembly along a first direction, such as the housing wall near the tab 201. The shape memory element extends along the first direction and has a first end facing the first wall, which is connected to the first wall. The other end of the shape memory element is a free end. This design ensures that the shape memory element contracts only in the first direction during phase transition, i.e., the contraction direction is consistent with the expansion direction of the electrode, generating a reverse constraint force that directly counteracts the Li-induced expansion of the electrode. + The expansion force generated by the embedding. The free end moves synchronously with the electrode to avoid stress concentration, and the reverse constraint force can significantly reduce the electrode expansion rate; ultimately, it alleviates the extrusion pressure of the electrode on the top cover / bottom wall and reduces the risk of shell breakage.

[0027] In one embodiment, the housing has a second wall located at the other end of the electrode assembly along the first direction, and the shape memory element has a second end facing the second wall, which is connected to the second wall. In this embodiment, both ends of the shape memory element are fixed, but at least one end needs to be configured as an elastic connection to facilitate deformation of the shape memory element. The elastic connection can be any material with high elasticity, high adhesion, ability to match the operating temperature of the battery cell, and resistance to electrolyte corrosion, specifically such as silicone rubber, thermoplastic elastomer, epoxy resin, or polyurethane.

[0028] An insulating component 202 is connected between the first end and the first wall, and between the second end and the second wall, such as... Figure 2 As shown, the insulating component 202 can physically block the current conduction path and prevent short circuits.

[0029] This solution utilizes the phase change shrinkage characteristics of the shape memory element in the buffer structure to dynamically release stress during electrode expansion, thereby reducing the internal pressure of the shell. This helps to improve the impact and compression resistance of the thinner shell and extend its cycle life.

[0030] It is understandable that the shape memory device undergoes pre-processing (i.e., stretching) to a second shape, the length of which is greater than the width of the active material layer on the electrode, storing elastic potential energy. During battery cell cycling, the cell heats up, and the electrode is affected by Li... + When the embedded part expands, the shape memory element transforms from the second shape to the contracted state (first shape). The contraction of the shape memory element generates a reverse constraint force, which can counteract the expansion force of the electrode and reduce the extrusion pressure of the electrode on the shell. As a result, the internal pressure of the shell is significantly reduced, and the risk of impact / extrusion fracture of the shell is reduced. At the same time, the expansion of the electrode is suppressed, the concentration of interfacial stress is relieved, and the cycle life is extended.

[0031] In one embodiment, the electrode includes a current collector and an active material layer disposed on the surface of the current collector. The electrode has an edge along a first direction, and the parallelism between the shape memory element and the electrode edge is 0~0.5mm.

[0032] The parallelism between the shape memory element and the electrode edge is to ensure the accuracy of the shape memory element and avoid uneven stress distribution caused by misalignment during subsequent winding / stacking. Specifically, the parallelism is 0.1mm, 0.2mm, 0.3mm, 0.4mm, or any value within the above range.

[0033] In one embodiment, the electrode includes a current collector and an active material layer disposed on the surface of the current collector. In a first direction, the first shape length L1 of the shape memory device is greater than the width L2 of the active material layer, satisfying: L2 = α × L1, where the value of α ranges from 80% to 95%. It is understood that L1 > L2 helps the shape memory device cover the active material layer, and the shrinkage force is evenly distributed at the edge of the electrode, avoiding local stress concentration; it can also match the shrinkage strain. The length difference between L1 and L2 determines the shrinkage strain ε = (1 / α) - 1 (e.g., ε = 11% when α = 90%), which helps match the electrode expansion rate. For example, the expansion of graphite negative electrode lithium intercalation is 5-10%, which effectively suppresses expansion and reduces the risk of shape memory device breakage due to excessive strain.

[0034] In one embodiment, under the second shape, the pre-stretch strain of the shape memory element is 3%-5%.

[0035] When the pre-tension strain is less than 3%, it is difficult to store sufficient stress. When the pre-tension strain is greater than 5%, it will lead to difficulties in initial installation or fatigue fracture. Specifically, it can be 4% or any value within the above range.

[0036] The formula for calculating the pre-stretch strain of the shape memory component is: (L3-L1) / L1, where L3 is the length of the second shape and L1 is the length of the first shape.

[0037] The pre-stretching strain process of the shape memory device is as follows: the first shape of the shape memory device is the austenitic phase shape maintained when the temperature is above the high-temperature phase transformation end temperature; the second shape of the shape memory device is the temporary shape obtained by the shape memory device through martensitic phase plastic deformation when the temperature is below the low-temperature phase transformation end temperature. When the temperature rises from below the low-temperature phase transformation end temperature to above the high-temperature phase transformation end temperature, the second shape of the shape memory device transforms into the austenitic phase through martensite inversion, restoring to the first shape.

[0038] In one embodiment, the buffer structure further includes a buffer layer, with a shape memory element disposed on the side surface of the buffer layer facing the electrode and / or diaphragm, or the shape memory element is disposed in the buffer layer and covered by the buffer layer.

[0039] The shape memory element is placed in the buffer layer to help limit its position, and the buffer layer also helps to provide buffer space during the electrode expansion process.

[0040] In one embodiment, the thickness of the buffer layer is greater than the diameter of the shape memory device. For example, the thickness h of the buffer layer satisfies 80μm < h ≤ 200μm. This helps the buffer layer cover the shape memory device, ensuring insulation safety when the shape memory device is made of metal, while also preventing the shape memory device from being too thick and affecting the energy density.

[0041] In one embodiment, the porosity of the buffer layer is 20%-30%. A porosity of less than or equal to 30% helps to improve the insulation safety between the positive and negative electrodes, while a porosity of greater than or equal to 20% helps to retain elasticity, absorb some of the thermal expansion stress, and prevent the buffer layer from cracking.

[0042] Specifically, the thickness h of the buffer layer satisfies 85μm, 100μm, 120μm, 150μm, 180μm, 190μm or any value within the above range; the porosity of the buffer layer is 22%, 25%, 28% or any value within the above range.

[0043] In one embodiment, the buffer layer is an insulating adhesive layer. For example, when the surface of the shape memory component is not insulating, the buffer layer is made of an insulating material, and the shape memory component is disposed in the buffer layer and covered by the buffer layer.

[0044] In another embodiment, when an insulating layer is provided on the surface of the shape memory device, the shape memory device is disposed on the surface of the buffer layer. The material of the buffer layer may include adhesives and conductive agents, which helps to improve the migration of active ions between the positive and negative electrodes.

[0045] The insulation layer material requirements include: wide operating temperature range (e.g., -40℃ to 120℃) to match the cell's operating temperature and prevent thermal runaway in extreme conditions; good insulation performance (insulation resistance ≥100MΩ after 1000 cycles) to ensure safe operation; and good matching with the electrode's coefficient of thermal expansion (CTE), such as an error ≤±2×10⁻⁶ CTE. -6 / ℃ can avoid thermal expansion mismatch stress caused by temperature fluctuations during charge and discharge cycles, which can lead to peeling of the adhesive layer from the electrode; good adhesion, such as peel strength from the electrode ≥5N / cm, can avoid peeling of the adhesive layer caused by mechanical vibration; dielectric strength of the insulating adhesive layer ≥20kV / mm, can avoid the risk of adhesive layer breakdown during high-rate charge and discharge.

[0046] The materials of the insulating adhesive layer that meet the above requirements include: (1) a mixture of 85wt%~95wt% epoxy resin base (epoxy equivalent 180g / eq-200g / eq, viscosity 500mPa•s-1000mPa•s), 5wt%-10wt% silica filler with particle size 5μm-10μm, and 1wt%-3wt% coupling agent (KH-550). Among them, epoxy resin base is the main material of the insulating adhesive layer, which has high insulation and dielectric strength. Its glass transition temperature Tg when the epoxy equivalent is 180g / eq-200g / eq is ≈80℃~100℃, which is basically matched with the working temperature of the battery cell; silica filler is used to improve CTE matching; coupling agent (KH-550) is used to improve interfacial adhesion.

[0047] (2) A mixture consisting of 93wt%-97wt% polyurethane base (70% solid content, viscosity 300mPa•s-600mPa•s), 2wt%-5wt% carbon fiber, and 0.5wt%-2wt% antioxidant (1010). Among them, the polyurethane base, as the main material of the insulating adhesive layer, has high insulation and dielectric strength, but it is prone to aging when heated. The antioxidant is used to match the working temperature of the battery cell. The thermal conductivity is poor, and the thermal conductivity is improved by carbon fiber.

[0048] (3) A compound composed of 96wt%-98wt% acrylate groups (epoxy equivalent 450g / eq-500g / eq, viscosity 800mPa•s-1200mPa•s), 1wt%-3wt% nano-alumina with a particle size of 9nm-11nm, and 0.1wt%-1wt% photoinitiator (1173). Among them, the acrylate group is the main material of the insulating adhesive layer. The high epoxy equivalent acrylate basically has high insulation and anti-aging properties, and the nano-alumina further improves the dielectric strength, meeting the requirements of the insulating adhesive layer.

[0049] The thickness of the insulating adhesive layer ranges from 50μm to 100μm.

[0050] This thickness range ensures insulation reliability, such as an insulation resistance ≥100MΩ after 1000 cycles, while also ensuring stress transfer efficiency. For example, too thin a layer is prone to breakdown, while too thick a layer will reduce the strain response speed of the SMA filament. Specifically, the thickness range of the insulating adhesive layer is 60μm, 80μm, 90μm, or any value within the above range.

[0051] In this design, an insulating adhesive layer is coated on the surfaces of the positive and negative electrodes to isolate the shape memory device from the electrodes, preventing direct contact between the shape memory device and the electrodes that could lead to a short circuit, and providing initial holding force for the shape memory device. Additionally, since the separator is located between the positive and negative electrodes, it separates them to prevent electron conduction from causing a short circuit, and provides a transport channel for lithium ions. Therefore, the two work synergistically to ensure the safety and reliability of the battery.

[0052] In one embodiment, such as Figure 1 As shown, the shape memory device is a shape memory alloy wire 104. The martensitic-austenitic phase transformation stress (400MPa-600MPa) of the shape memory alloy wire provides the core driving force to suppress electrode expansion; the phase transformation temperature (40℃-80℃) ensures precise matching with the battery's operating temperature range; and the fatigue life (≥1000 cycles) guarantees functional stability during long-term cycling. These three aspects jointly support the core capability of the shape memory alloy wire as a shape memory device—dynamically offsetting electrode expansion through phase transformation contraction, solving the problems of insufficient impact resistance and short cycle life in thinner and lighter casings.

[0053] In one embodiment, the diameter d of the shape memory alloy wire satisfies 80μm≤d<200μm.

[0054] Shape memory alloy wires are prone to breakage when their diameter is less than 80 μm, but are easily deformed by plasticity when their diameter is greater than 200 μm. Specifically, the diameter d of the shape memory alloy wire can be 90 μm, 120 μm, 150 μm, 180 μm, or any value within the above range.

[0055] The shape memory alloy wires are numerous, such as 10-30 wires, and are arranged alternately.

[0056] When the number of wires is less than 10, the resulting stress distribution is uneven; however, when the number exceeds 30, it increases internal resistance and manufacturing complexity. Specifically, the number of shape memory alloy wires is 15, 20, 25, or any value within the aforementioned range. Furthermore, spacing ensures a more uniform contractile force on the electrode.

[0057] The materials used for shape memory alloy wires include at least one of Ni-Ti based alloys, Cu-based alloys, and Fe-based alloys. Ni-Ti based alloys possess a wide phase transformation temperature range (-50℃ to 150℃), large deformation, high stress (8-10%), high phase transformation stress (400-600MPa), and an ultra-long fatigue life of 10,000 cycles, making them suitable materials for shape memory alloy wires. Cu-based alloys, in addition to possessing the properties of Ni-Ti based alloys, also offer advantages such as low price; Fe-based alloys, besides exhibiting the properties of Ni-Ti based alloys, also possess advantages such as high strength and resistance to breakage.

[0058] Specifically, Ni-Ti based alloys include any one of Ni-Ti alloys, Ni-Ti-Cu alloys, and Ni-Ti-Hf alloys. Among them, the Ni:Ti atomic ratio in Ni-Ti alloys is 48:52~52:48; the Ni:Ti:Cu atomic ratio in Ni-Ti-Cu alloys is 48~50:49~51:0.5~2; and the Ni:Ti:Hf atomic ratio in Ni-Ti-Hf alloys is 47~49:49~51:1~5. Ni-Ti alloys, as a reference alloy, can provide balanced phase transformation characteristics and mechanical properties. The addition of Cu to Ni-Ti-Cu alloys can lower the relevant temperature, while the addition of Hf to Ni-Ti-Hf alloys can raise the relevant temperature.

[0059] Specifically, Cu-based alloys include Cu-Al-Ni alloys, where the Cu:Al:Ni atomic ratio is 55~65:28~38:5~10. In this alloy, Cu serves as the matrix element, providing basic mechanical properties. Al is used for low-temperature phase transformation control; excessive Al leads to an excessively high martensite transformation start temperature Ms, resulting in the loss of energy storage power at room temperature, while excessive Al reduces shape memory capability. Ni is used to maintain austenite stability; excessive Ni increases cost, while excessive Ni cannot stabilize the austenite phase.

[0060] Specifically, Fe-based alloys include Fe-Mn-Si alloys (where the atomic ratio of Fe:Mn:Si is 70~75:15~20:8~12). In this alloy, Fe serves as the matrix element, while Mn provides the basic mechanical properties. Mn is the key element that induces the martensitic phase transformation; too low a content will not stabilize the martensitic phase, while too high a content will lead to the precipitation of brittle phases. Si is used for solid solution strengthening of the austenitic phase and to suppress the martensitic inversion transformation at high temperatures. Too low a content will not increase the phase transformation temperature, while too high a content will increase brittleness.

[0061] In one embodiment, the shell thickness is 0.4 mm to 0.8 mm.

[0062] A shell thickness of less than 0.4 mm results in insufficient impact resistance, while a thickness greater than 0.8 mm would compromise the lightweight objective. Specifically, the shell thickness should be 0.5 mm, 0.6 mm, 0.7 mm, or any value within the aforementioned range.

[0063] In one embodiment, the thickness of the positive electrode active layer is 100 μm to 300 μm. The thickness of the negative electrode active layer is 80 μm to 200 μm. Specifically, the thickness of the positive electrode active layer is 150 μm, 180 μm, 200 μm, 250 μm, 280 μm or any value within the above range; the thickness of the negative electrode active layer is 100 μm, 120 μm, 150 μm, 180 μm or any value within the above range.

[0064] The active layer of the positive electrode includes at least one of the following materials: lithium cobalt oxide, nickel-cobalt-manganese ternary, lithium iron phosphate, and lithium manganese iron phosphate. These materials possess high electrochemical activity, stable crystal structure, and charge / discharge performance suitable for lithium battery systems, enabling efficient lithium-ion insertion / extraction. The active layer of the negative electrode includes at least one of the following materials: graphite, silicon-carbon, and lithium titanate. These materials enable efficient lithium-ion insertion / extraction and exhibit outstanding advantages in cycle stability, energy density, and fast-charging safety, respectively, and can meet the application requirements of different lithium batteries.

[0065] To better understand this solution, one embodiment also provides a method for installing shape memory alloy wires, specifically including: 1. Coat the electrode surface with an insulating adhesive layer and complete the initial positioning of the shape memory alloy wire.

[0066] Specifically, after the positive and negative electrode sheets are coated with the active material coating by a coating machine, they enter the insulating adhesive coating process (such as gravure printing or scraping), where an insulating adhesive layer is applied to the active area of ​​the electrode sheet. After the adhesive is applied (before the adhesive has cured), shape memory alloy wires are laid flat on the surface of the insulating adhesive layer at a designed spacing (such as 1mm-2mm) using a shape memory alloy wire positioning fixture (such as a grooved guide roller or a vacuum adsorption platform). The length of the shape memory alloy wire is greater than the width of the active material area of ​​the electrode sheet. Subsequently, the insulating adhesive layer cures, and the shape memory alloy wire and the insulating adhesive layer form an integrated structure, achieving precise positioning and functional coupling. Furthermore, the parallelism between the shape memory alloy wire and the edge of the electrode sheet is ≤0.5mm, avoiding uneven stress distribution caused by misalignment during subsequent winding / stacking.

[0067] 2. Cell assembly process.

[0068] Specifically, the pretreated positive and negative electrode sheets and the separator are stacked in the order of "positive electrode sheet → separator → negative electrode sheet → separator" and then wound into a core using a winding machine. Since the length of the shape memory alloy wire is greater than the width of the active material region, the two ends of the shape memory alloy wire will naturally be exposed at both ends of the core after winding.

[0069] After the core is completed, the exposed shape memory alloy wire ends (at least one end, preferably both ends) are fixed to the inside of the battery top cover (positive electrode side) or bottom wall (negative electrode side) by insulating glue or mechanical pressing.

[0070] The parallelism test method in step 1 is as follows: I. Preparations before the test 1. Environmental conditions Temperature: 25℃±1℃, used to avoid thermal expansion of the electrode / shape memory alloy wire due to temperature changes; Humidity: 50%RH±5%, used to prevent the electrode from absorbing moisture and deforming; Vibration: Vibration ≤5μm / s, avoid external interference.

[0071] 2. Sample fixation Electrode fixing: The electrode containing shape memory alloy wire is fixed on the test stage by vacuum adsorption or clamps, ensuring that the edge of the electrode is parallel to the test platform; Shape memory alloy wire fixing: The two ends of the shape memory alloy wire are bonded to the top cover / bottom wall through insulating parts. Before testing, it must be confirmed that there is no relative displacement between the shape memory alloy wire and the edge of the electrode.

[0072] II. Testing Procedures Using a Coordinate Measuring Machine 1. Establish a coordinate system Using the straight line at the edge of the electrode as the reference axis, select three non-collinear points (A, B, C) on the surface of the electrode. Measure the coordinates of these three points using a CMM and fit the equation of the reference straight line (e.g., y = kx + b).

[0073] 2. Measuring the linear equation of shape memory alloy wire Three non-collinear points (D, E, F) are selected on the shape memory alloy wire. The coordinates of these three points are measured by CMM, and the linear equation of the shape memory alloy wire (e.g., y = k'x + b') is fitted.

[0074] 3. Calculate the parallelism deviation Parallelism deviation is defined as the angle θ between two straight lines. The specific calculation is as follows: Angle deviation: θ = arctan|(k'–k) / (1+kk'; Where k is the slope of the reference line; k' is the slope of the actual measured line.

[0075] To better understand this solution, the following details the process of real-time adjustment of electrode expansion stress using shape memory alloy wire: 1. Initial state: The shape memory alloy wire is fixed between the positive and negative electrode plates with a pre-tensile strain of 3%-5%. The insulating adhesive layer isolates the electrode plates from the shape memory alloy wire and provides initial bonding force. The electrode plates do not expand. 2. Cyclic expansion stage: During battery charging and discharging, the electrode expands due to gas production, generating radial pressure that pushes the shape memory alloy wire to be further stretched to 5%-7% along the expansion direction; at the same time, the gas production reaction releases heat, causing the internal temperature of the battery to rise to 40℃-80℃. 3. Phase transformation stress release: When the temperature reaches the phase transformation temperature of the shape memory alloy wire, 40℃-80℃, the martensitic phase (low-temperature phase) transforms into the austenitic phase (high-temperature phase). The shape memory alloy wire generates a recovery stress of 400MPa-600MPa, which is much greater than the expansion pressure of the electrode. This recovery stress drives the shape memory alloy wire to contract, converting the expansion pressure of the electrode into the elastic strain energy of the shape memory alloy wire for storage, thereby reducing the internal pressure borne by the shell. 4. Cycle recovery stage: When the battery is left to cool to below 40°C, the shape memory alloy wire gradually cools and undergoes a reverse phase transformation (austenite → martensite), restoring the initial pre-stretched state and storing stress release capacity for the next cycle expansion.

[0076] One embodiment also provides a battery pack including the aforementioned battery cells.

[0077] One embodiment also provides an electrical device, which includes the battery pack described above, and the battery pack serves as the power supply for the electrical device.

[0078] For the above-described battery pack embodiments and electrical device embodiments, the positive electrode sheet includes a positive electrode active material layer, which includes the above-described positive electrode active material and can achieve the same technical effect. To avoid repetition, it will not be described again here. For relevant details, please refer to the description of the positive electrode active material embodiments.

[0079] To better explain this solution, embodiments and comparative examples are also provided below.

[0080] Example 1 1. Preparation of positive electrode sheet.

[0081] Material system: Lithium cobalt oxide active material with an areal density of 20 mg / cm² and a coating thickness of 150 μm; binder is 2 wt% polyvinylidene fluoride (PVDF), conductive agent is 1 wt% Super P; current collector is 12 μm thick aluminum foil.

[0082] Preparation steps: 1.1. Slurry preparation: PVDF was dissolved in N-methylpyrrolidone (NMP) (solid content 5wt%), lithium cobalt oxide (D50=12μm) and Super P (D50=40nm) were added, and the mixture was stirred and dispersed at 3000rpm for 2h to obtain a positive electrode slurry with a solid content of 70wt%.

[0083] 1.2. Coating and Drying: The positive electrode slurry is coated onto the current collector (aluminum foil) and dried to obtain an electrode sheet with a thickness of 160 μm (coating 150 μm + aluminum foil 10 μm).

[0084] The transfer coating machine has a die head gap of 150μm and a travel speed of 30m / min. The drying temperature is 120℃, and the drying time is 3 hours. The linear pressure of the roller compaction is 800N / cm.

[0085] 1.3. Slitting and processing: The above electrode sheets are slitted to obtain electrode sheets with a width of 100 mm and a length of 160 mm (140 mm of active area, with 20 mm of uncoated active material left at the edge). The electrode sheets are then placed under vacuum and dried at 80°C for 12 hours until the moisture content is below 200 ppm.

[0086] 2. Preparation of negative electrode sheet.

[0087] Material system: Silicon-carbon composite material (Si / C, Si content 15wt%) active material, areal density 15mg / cm², coating thickness 130μm; binder is a mixture of sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), wherein the mass fractions of sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) are 1.5wt% each; conductive agent is 1wt% carbon nanotubes (CNTs); current collector is 8μm copper foil.

[0088] Preparation steps: 2.1. Slurry preparation: CMC was dissolved in deionized water (solid content 1wt%), and SBR (solid content 5wt%) was added. Then silicon-carbon composite material (Si particle size 50nm, C coating 10nm) and CNT (tube diameter 8nm, length 10μm) were added. The mixture was ball-milled and dispersed at 300rpm for 4h to obtain a negative electrode slurry with a solid content of 60wt%.

[0089] 2.2. Coating and Drying: The negative electrode slurry is coated onto the current collector (copper foil) and dried to obtain an electrode sheet with a thickness of 140 μm (coating 130 μm + copper foil 10 μm).

[0090] The extrusion coating machine has a die head gap of 130μm and a travel speed of 25m / min; drying is done by hot air drying at 80℃ for 3 hours; and the linear pressure of roller compaction is 600N / cm.

[0091] 2.3. Pretreatment: Cut the above electrode sheets to obtain electrode sheets with a width of 100 mm and a length of 160 mm (140 mm of active area, with 20 mm of uncoated active material left at the edge), and vacuum dry them at 120℃ for 24 h to ensure that the moisture content is <100 ppm.

[0092] 3. Diaphragm.

[0093] 3.1. Diaphragm Structure and Material Selection Base membrane: A 5μm ultrathin PE (polyethylene) membrane is selected as the supporting framework; Adhesive layer: Coated with PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) copolymer (solid content 10wt%, viscosity 800mPa·s) with a thickness of 2μm to enhance the adhesion between the diaphragm and the electrode; Ceramic layer: Alumina nanoparticles (200nm particle size, 99.9% purity) with a thickness of 2μm are coated on one side to improve puncture resistance and thermal stability.

[0094] 3.2. Diaphragm Preparation Process Step 1: Base film pretreatment The PE base film was subjected to corona treatment (100W power, 60s time), which increased the surface energy from 30mN / m to 45mN / m, thus enhancing the adhesion of adhesives.

[0095] Step 2: Applying the adhesive layer A microgravure coating machine was used to coat one side of a PE base film with PVDF-HFP adhesive (solvent: acetone:DMF=7:3). The die gap of the coating machine was 2μm, and the travel speed was 15m / min. After coating, the solvent was removed by hot air drying at 80℃ for 3 hours, forming a uniform adhesive layer with a thickness of 2μm.

[0096] Step 3: Ceramic layer coating Preparation of ceramic slurry: 200nm alumina particles and 1wt% PVDF-HFP dispersant were ball-milled and dispersed in NMP solvent for 2 hours to obtain a ceramic slurry with a solid content of 20wt%. The ceramic slurry was then coated onto the adhesive layer surface (on the same side as the adhesive layer) using a doctor blade coater. The doctor blade coater had a die gap of 2μm and a travel speed of 10m / min. After drying in a 120℃ oven for 30 minutes, the ceramic particles were uniformly adhered to the adhesive layer (thickness 2μm, ceramic content ≥80wt%).

[0097] 4. Preparation of electrolyte.

[0098] Formulation: Dissolve 1.1M LiPF6 in a system with a volume ratio of EC:DEC:EMC=3:5:2, add 2wt% VC+1wt% FEC to obtain the electrolyte.

[0099] 5. Battery assembly.

[0100] 5.1. An insulating adhesive layer is coated on the surface of the positive electrode. After the insulating adhesive layer cures, the shape memory alloy wires are arranged and positioned. The pre-stretch strain of the shape memory alloy wires is 3%. Ten shape memory alloy wires are spaced apart in the insulating adhesive layer. The diameter of the shape memory alloy wires is 100 μm. The parallelism between the shape memory alloy wires and the edge of the electrode is 0.3 mm. The first shape length L1 of the shape memory element is greater than the width L2 of the active material layer, satisfying: L2 = α × L1, where α is 90%. 5.2 After the electrode and separator are wound into a cylindrical core by the winding machine, a shape memory alloy wire is inserted into the "positive electrode-separator" interface of the core according to the arrangement and positioning, and the shape memory alloy wire is ensured to be located between the active area of ​​the positive electrode and the separator.

[0101] 5.3 Fix both ends of the shape memory alloy wire and inject electrolyte into the cell to obtain the battery.

[0102] Specifically, fixing the two ends of the shape memory alloy wire involves applying a 50μm thick insulating adhesive (i.e., insulating component 202) to corresponding positions on the inner sides of the top and bottom covers. The two ends of the shape memory alloy wire are then pressed into the insulating adhesive, ensuring full connection between the adhesive, the wire, and the housing. Finally, curing is performed by heating at 60℃ for 30 minutes.

[0103] The battery parameters include: a capacity of 314Ah; internal dimensions of the casing of 150mm×100mm×20mm; a casing of 0.45mm thick aluminum; a positive electrode material of lithium cobalt oxide with an active material coating thickness of 150μm and an areal density of 20mg / cm²; and a negative electrode material of silicon-carbon composite material with an active material coating thickness of 130μm and an areal density of 15mg / cm².

[0104] The shape memory alloy wire parameters include: material is Ni-Ti alloy (atomic ratio Ni:Ti = 48:52); diameter is 100um; length of shape memory alloy wire is 160mm, covering the active area of ​​the electrode for 140mm; pre-tension strain is 3%; quantity is 10 wires; uniformly distributed along the length of the electrode with a spacing of 1.2mm.

[0105] Insulating adhesive layer parameters: The material is 96wt% polyurethane-based adhesive (70% solid content, 600mPa•s viscosity) + 3wt% carbon fiber (7μm diameter, 100 aspect ratio) + 1wt% antioxidant (1010); the thickness is 80μm.

[0106] Examples 2-3, 17-18 The only difference from Example 1 is the different pre-stretch strain of the shape memory alloy wire.

[0107] Examples 4-5, 19-20 The only difference from Example 1 is the diameter of the shape memory alloy wire.

[0108] Examples 6-8, 21 The only difference from Example 1 is that the parallelism between the shape memory alloy wire and the edge of the electrode is different.

[0109] Examples 9-10, 22-23 The only difference from Example 1 is the ratio α of the length of the active material layer to the length of the shape memory alloy wire.

[0110] Examples 11-14 The only difference from Example 1 is the material of the shape memory alloy wire.

[0111] Examples 15-16, 24-25 The only difference from Example 1 is the number of shape memory alloy wires.

[0112] Examples 26-27 The only difference from Example 1 is the thickness of the buffer layer.

[0113] Comparative Example 1 The only difference from Example 1 is that there is no shape memory alloy wire.

[0114] The parameters in the above embodiments are shown in Table 1. Additionally, the following performance tests were performed on the batteries in the above embodiments and comparative examples: (1) Cyclic internal pressure change test: A thin film pressure sensor is installed inside the test cell housing to record the initial internal pressure. At 25℃, 1C charging / 1C discharging is performed. After 1000 cycles, the internal pressure after the cycle is recorded. The cyclic internal pressure ΔP = P after the cycle - P initial.

[0115] (2) Compression resistance: Maximum deformation of aluminum shell under 1kN load. Place the battery between the upper and lower clamps of the testing machine, ensuring that the side of the aluminum shell is in contact with the clamps. Then start the test: the testing machine compresses the battery at a constant speed of 1mm / min; simultaneously record real-time load (N) and displacement (mm) data (via data acquisition system); observe the battery status (e.g., whether there is leakage, bulging, or broken tabs), and terminate the test if it fails prematurely. After the test, the maximum deformation of the aluminum shell is the maximum displacement value read from the displacement sensor during the compression process; (3) Impact resistance: The battery was dropped freely from a height of 1m, with each of the 6 sides of the battery dropping once, and the maximum deformation of the casing was recorded.

[0116] (4) Cycle life: The battery is charged and discharged at 1C at 25℃. After 1000 cycles, the capacity retention rate is tested. Capacity retention rate = capacity after cycle / initial capacity.

[0117] (5) Insulation reliability: After 1000 cycles, the cell was disassembled to obtain the electrode (containing the insulating adhesive layer and shape memory alloy wire), and then the insulation resistance between the electrode and the shape memory alloy wire was tested using a megohmmeter (500V DC, 60s). (At least 5 points were measured between the active area of ​​the electrode and the insulating adhesive layer, and the average value was taken). The test data are shown in Table 2 below.

[0118] Table 1. List of parameters in the examples and comparative examples

[0119] Table 2. Performance test data of batteries in the examples and comparative examples.

[0120] As can be seen from Tables 1 and 2, the performance of the embodiments is improved compared to the comparative examples.

[0121] Understandably, the pre-stretch strain determines the "elastic energy storage capacity" of the shape memory alloy wire. A pre-stretch strain of 3% to 5% helps the shape memory alloy wire maintain good elastic recovery and provides expansion space for the electrode, reducing the pressure of the expanded electrode on the shell. The diameter of the shape memory alloy wire determines its "stiffness" and "contact area." If the diameter is too small, the stiffness is insufficient to support the electrode; however, if the diameter is too large, the excessive contact area can easily lead to localized stress concentration. The diameter d of the shape memory element should further satisfy 80μm ≤ d < 200μm to improve its support performance and reduce stress concentration. Parallelism determines the "uniformity of distribution" of the shape memory alloy wire. A parallelism of 0 to 0.5 mm helps to evenly distribute the wire and reduce uneven expansion forces on the electrode. α determines the "coverage range" and "fixed margin" of the shape memory alloy wire. If α is too small, it cannot cover the expansion area at the edge of the electrode. However, if α is too large, it is prone to detachment during cycling due to the lack of a fixed margin. The value range of α is further set to 80%~95%, which helps reduce the risk of shape memory alloy wire detachment. The number of shape memory alloy wires determines the "support force" and "insulation performance." Too few wires will result in insufficient support force, while too many wires will cause them to squeeze against each other, leading to a decrease in insulation resistance. The thickness of the buffer layer determines the "insulation strength" and "adhesion." If the thickness is too thin, it is easily punctured, but if it is too thick, it will reduce the adhesion.

[0122] The above examples illustrate the present invention only to aid in understanding it and are not intended to limit the scope of the invention. Those skilled in the art can make various simple deductions, modifications, or substitutions based on the principles of this invention.

Claims

1. A battery cell, characterized in that, The battery cell includes a housing and an electrode assembly. The housing covers the electrode assembly. The electrode assembly includes an electrode plate and a separator (103). The electrode plate includes a positive electrode plate (101) and a negative electrode plate (102). The separator (103) is located between the positive electrode plate (101) and the negative electrode plate (102). The battery cell also includes a buffer structure located between the positive electrode (101) and the separator (103), and / or, the buffer structure located between the negative electrode (102) and the separator (103); The electrode assembly has a first direction, the housing has a first wall located at one end of the electrode assembly along the first direction, and the buffer structure includes a shape memory element that extends along the first direction and has a first end facing the first wall, the first end being connected to the first wall. The shape memory device has a first shape and a second shape, wherein the length L3 of the second shape is greater than the length L1 of the first shape, the length L3 of the first shape is obtained by testing the shape memory device at a temperature of 50℃-60℃, and the length L1 of the first shape is obtained by testing the shape memory device at a temperature of 25℃-35℃.

2. The battery cell according to claim 1, characterized in that, In the second shape, the pre-stretch strain of the shape memory element is 3% to 5%.

3. The battery cell according to claim 1, characterized in that, An insulating component is connected between the first end and the first wall; And / or, the housing has a second wall located at the other end of the pole group along the first direction, the shape memory element has a second end facing the second wall, the second end being connected to the second wall; an insulating element is connected between the second end and the second wall.

4. The battery cell according to claim 1, characterized in that, At least one of the following conditions must be met: A. The diameter d of the shape memory device satisfies 80μm≤d<200μm; B. The number of shape memory components is multiple, and the multiple shape memory components are arranged at intervals; C. The shape memory component includes shape memory alloy wire.

5. The battery cell according to claim 1, characterized in that, The electrode includes a current collector and an active material layer disposed on the surface of the current collector. The electrode has an edge along the first direction, and the parallelism between the shape memory element and the edge of the electrode is 0~0.5mm. And / or, the electrode includes a current collector and an active material layer disposed on the surface of the current collector, wherein in the first direction, the length L1 of the first shape of the shape memory element is greater than the width L2 of the active material layer, satisfying: L2=α×L1, where the value of α ranges from 80% to 95%.

6. The battery cell according to claim 1, characterized in that, The material of the shape memory device includes at least one of Ni-Ti based alloy, Cu based alloy, and Fe based alloy.

7. The battery cell according to claim 6, characterized in that, The Ni-Ti based alloy includes Ni-Ti alloy, Ni-Ti-Cu alloy, or Ni-Ti-Hf alloy; and / or, the Cu based alloy includes Cu-Al-Ni alloy; and / or, the Fe based alloy includes Fe-Mn-Si alloy.

8. The battery cell according to claim 1, characterized in that, The buffer structure further includes a buffer layer located between the electrode and the diaphragm (103), and the shape memory element is disposed on the side surface of the buffer layer facing the electrode and / or the diaphragm (103); or, the shape memory element is disposed in the buffer layer and covered by the buffer layer.

9. The battery cell according to claim 8, characterized in that, The thickness of the buffer layer is greater than the diameter of the shape memory element, and the thickness h of the buffer layer satisfies 80μm < h ≤ 200μm; and / or, the porosity of the buffer layer is 20%~30%.

10. The battery cell according to claim 8, characterized in that, The buffer layer is an insulating adhesive layer; the surface of the shape memory component is provided with an insulating layer, and the buffer layer includes an adhesive and a conductive agent.

11. A battery pack, characterized in that, The battery pack includes the battery cells according to any one of claims 1 to 10.

12. An electrical appliance, characterized in that, The electrical device includes the battery pack of claim 11, which serves as the power supply for the electrical device.

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