Sodium-ion battery pole piece, preparation method thereof and battery

Abstract

The application provides a sodium ion battery pole piece, a preparation method thereof and a battery, and relates to the technical field of sodium ion batteries.The sodium ion battery pole piece provided by the application comprises a current collector, an active material layer and a circuit-breaking coating layer arranged between the current collector and the active material layer; the circuit-breaking coating layer is a conductive coating layer and has a volume expansion characteristic of thermal sensitivity and / or pressure sensitivity.The application utilizes the characteristics of the thermal / pressure sensitive coating layer in expanding and breaking the circuit under an abnormally high temperature or high pressure, rapidly cuts off the electrical connection between the current collector and the active layer when an internal short circuit occurs in the battery, blocks the short-circuit current and heat accumulation, effectively prevents thermal runaway and improves the safety of the battery.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and more specifically, to a sodium-ion battery electrode, its preparation method, and the battery itself. Background Technology

[0002] With the rapid development of new energy technologies, sodium-ion batteries have shown great application potential in energy storage and power battery fields due to their abundant resources and low cost. However, battery safety remains one of the key factors restricting their large-scale commercial application. Sodium-ion batteries have a complex internal structure, and their electrochemical system is highly sensitive to environmental and physical conditions. Even minor internal defects or external abnormal disturbances can evolve into serious safety hazards. Therefore, improving their safety performance under various operating conditions has become a focus of industry attention.

[0003] During the actual manufacturing process of battery cells, due to limitations in process control, it is difficult to completely avoid the introduction of foreign matter and impurities such as metal shavings and electrode burrs. If these tiny foreign objects remain inside the battery, they can easily puncture the separator and damage the insulation between the positive and negative electrodes. In addition, batteries face complex external environments during subsequent transportation, storage, or actual use. If subjected to mechanical abuse such as squeezing or collisions, the battery cell will deform under stress, thereby damaging the integrity of the internal structure and causing displacement, deformation, or even breakage of the positive and negative electrode materials.

[0004] The most direct consequence of the aforementioned manufacturing defects or mechanical misuse is the induction of internal short circuits within the battery cell. Once an internal short circuit occurs, a massive short-circuit current is generated at the short-circuit point, instantly producing a large amount of heat due to the resistive heating effect. Simultaneously, the short circuit triggers the rapid release of stored electrical energy within the cell, further exacerbating heat generation. When the local temperature rises sharply, it can cause the separator to thermally shrink or even melt and deform, increasing the contact area between the positive and negative electrodes and further worsening the short circuit, thus creating a vicious cycle of "heating up - worsening short circuit - regenerative heat."

[0005] This vicious cycle eventually leads to heat accumulation exceeding a critical point, triggering thermal runaway within the battery cell. At this point, the internal chemical reactions become uncontrollable, decomposing and releasing large amounts of flammable gases and high heat, which can easily cause the battery cell to smoke, catch fire, or even explode, resulting in severe property damage and safety accidents. Therefore, an effective technical means is urgently needed to block this thermal runaway chain caused by internal short circuits and improve the inherent safety of batteries.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a sodium-ion battery electrode, its preparation method, and the battery itself. The sodium-ion battery electrode utilizes a thermistor / piezoresistive coating to expand and break the circuit under abnormal operating conditions, thereby blocking short-circuit current and thermal runaway, and improving battery safety.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a sodium-ion battery electrode, comprising a current collector, an active material layer, and a circuit-breaking coating disposed between the current collector and the active material layer; The circuit-breaking coating is a conductive coating and has thermosensitive and / or piezoresistive volume expansion characteristics. When the temperature of the circuit-breaking coating is lower than the predetermined trigger temperature and / or the pressure on the circuit-breaking coating is lower than the predetermined trigger pressure, the circuit-breaking coating remains conductive, so that the active material layer is electrically connected to the current collector; When the temperature of the circuit-breaking coating reaches or exceeds the predetermined trigger temperature and / or the pressure on the circuit-breaking coating reaches or exceeds the predetermined trigger pressure, the circuit-breaking coating can undergo volume expansion, causing the active material layer to separate from the current collector at least partially, thereby interrupting the electrical connection between the active material layer and the current collector.

[0009] In an optional embodiment, the electrode is a sodium-ion battery positive electrode, the active material layer is a positive electrode active material layer, and the current collector is a positive electrode current collector; Preferably, the positive electrode active material in the positive electrode active material layer includes at least one of layered oxide, polyanionic material, Prussian blue, and Prussian white; Preferably, the compaction density of the sodium-ion battery positive electrode sheet is 1.5 g / cm³. 3 ~3.5g / cm 3 ; Preferably, the positive electrode active material layer is a positive electrode active material layer formed by coating both sides of the positive electrode current collector, and the circuit breaking coating is disposed between the positive electrode current collector on each side and the corresponding positive electrode active material layer.

[0010] In an optional embodiment, the electrode is a sodium-ion battery negative electrode, the active material layer is a negative electrode active material layer, and the current collector is a negative electrode current collector; Preferably, the negative electrode active material in the negative electrode active material layer includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, and graphene; Preferably, the compaction density of the sodium-ion battery negative electrode sheet is 0.5 g / cm³. 3 ~1.5g / cm 3 .

[0011] In an optional embodiment, the thickness of the circuit-breaking coating is not less than 10 μm; and / or, The coefficient of thermal expansion of the circuit-breaking coating is not less than 50 × 10⁻⁶. -6 K -1 ; and / or, The volume expansion rate of the circuit-breaking coating is not less than 10%; and / or, The conductivity of the circuit-breaking coating is not less than 1.0 S / cm; and / or, The coating material forming the circuit-breaking coating is soluble in an organic solvent; preferably, the organic solvent includes at least one of N-methylpyrrolidone, dimethyl sulfoxide, cresol, and ethanol.

[0012] In an optional embodiment, the circuit-breaking coating comprises at least one of the following materials: carbon nanotube / polymer composite material, poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid, polyaniline, polypyrrole monomers or modified polymer materials, and metal / alloy foam materials. Preferably, the circuit-breaking coating comprises a green imine salt of polyaniline.

[0013] Preferably, the circuit-breaking coating comprises emerald green imine salt, polytetrafluoroethylene, and carbon nanotubes; preferably, the mass ratio of emerald green imine salt, polytetrafluoroethylene, and carbon nanotubes is (7.0~9.0):(0.5~1.5):(0.5~1.5); preferably, the mass percentage W of emerald green imine salt in the circuit-breaking coating satisfies: 70%≤W≤90%.

[0014] In an optional embodiment, the circuit-breaking coating is formed by at least one of the following methods: dip coating, hot pressing, particle deposition, chemical vapor deposition, physical vapor deposition, spin coating, plasma spraying, gravure coating, microgravure coating, and dispensing coating.

[0015] Secondly, the present invention provides a method for preparing a sodium-ion battery electrode as described in any of the foregoing embodiments, comprising: A circuit breaking coating slurry is applied to the surface of the current collector and a first drying process is performed to form a circuit breaking coating on the surface of the current collector. An active material layer slurry is coated onto the surface of the circuit-breaking coating and then subjected to a second drying process to form an active material layer. The electrode sheet with the active material layer formed thereon is rolled to obtain the sodium-ion battery electrode sheet.

[0016] In some embodiments, the drying conditions for the first drying treatment and / or the second drying treatment include: a temperature of 30°C to 120°C; and / or a wind frequency of 10Hz to 50Hz; and / or... The coating speed of the active material layer slurry is 1 m / min to 45 m / min; and / or, The circuit breaking coating slurry is applied to the surface of the current collector by microgravure coating.

[0017] Thirdly, the present invention provides a circuit breaking coating slurry for forming a circuit breaking coating as described in any of the foregoing embodiments, wherein the circuit breaking coating slurry comprises emerald green imine salt, polytetrafluoroethylene, carbon nanotubes, and the solvent N-methylpyrrolidone. Preferably, the mass ratio of the emerald green imine salt, the polytetrafluoroethylene, and the carbon nanotubes is (7.0~9.0):(0.5~1.5):(0.5~1.5). Preferably, the circuit breaker coating slurry is ultrasonically dispersed before coating.

[0018] Fourthly, the present invention provides a sodium-ion battery, comprising a positive electrode, a negative electrode, and a separator; Wherein, at least one of the positive electrode and the negative electrode is a sodium-ion battery electrode as described in any of the foregoing embodiments.

[0019] Fifthly, the present invention provides an electrical device including a sodium-ion battery as described in the foregoing embodiments.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: The sodium-ion battery electrode provided in this application effectively improves battery safety by setting a circuit-breaking coating with thermosensitive and / or piezoresistive volume expansion characteristics between the current collector and the active material layer. Under normal battery operating conditions at low temperatures or low pressures, this circuit-breaking coating maintains good conductivity, ensuring normal electrical connection between the active material layer and the current collector, thus not affecting the battery's charging and discharging functions. However, when the battery experiences internal short circuits due to manufacturing defects such as internal metal foreign object punctures or electrode burrs, or due to external mechanical abuse such as squeezing or collisions, leading to abnormal local temperature increases or abnormal internal pressure increases, the circuit-breaking coating responds rapidly and undergoes volume expansion.

[0021] This volume expansion physically pushes the active material layer away from the current collector, achieving local or overall separation between the two, thereby rapidly cutting off the electron transport path between the active material and the current collector. Blocking the electron path significantly reduces or even eliminates the short-circuit current, suppressing heat accumulation caused by resistive heating at its source. This prevents the vicious cycle of thermal shrinkage of the separator due to internal short circuits, further deteriorating the battery cell and preventing serious safety accidents such as thermal runaway, fire, or explosion. It significantly improves the inherent safety of sodium-ion batteries under manufacturing defects or mechanical abuse conditions. Attached Figure Description

[0022] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 This is a schematic flowchart of the method for preparing sodium-ion battery electrodes in the embodiments of this application; Figure 2 This is a trend graph showing the relationship between the content of emerald green imine salt (ES) and the thermal expansion properties and surface quality (powder shedding) of the circuit-breaking coating in different embodiments and comparative examples of this application. The graph shows that as the ES content increases, the thickness increment of the coating at 100°C increases, but powder shedding occurs when the content reaches 90% or more. Figure 3 This is a bar chart comparing the battery internal resistance (ACR and DCR at 50% SOC) of different embodiments and comparative examples of this application; the figure shows that the internal resistance of Comparative Example 1 (pure ES coating) is significantly higher than that of Examples 1-5 and Comparative Example 2 (no coating), while the internal resistance of Examples 1-5 is basically the same as that of Comparative Example 2. Detailed Implementation

[0024] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0025] This application provides a sodium-ion battery electrode, including a current collector, an active material layer, and a circuit-breaking coating disposed between the current collector and the active material layer. The circuit-breaking coating is a conductive coating and has thermosensitive and / or piezoresistive volume expansion characteristics. When the temperature of the circuit-breaking coating is lower than a predetermined trigger temperature and / or the pressure on the circuit-breaking coating is lower than a predetermined trigger pressure, the circuit-breaking coating remains conductive, electrically connecting the active material layer and the current collector. When the temperature of the circuit-breaking coating reaches or exceeds the predetermined trigger temperature and / or the pressure on the circuit-breaking coating reaches or exceeds the predetermined trigger pressure, the circuit-breaking coating undergoes volume expansion, causing at least partial separation between the active material layer and the current collector, thereby interrupting the electrical connection between the active material layer and the current collector.

[0026] In this embodiment, the sodium-ion battery electrode exhibits a multilayer composite structure in its microstructure. It mainly comprises three core components: (1) Current collector, which serves as the substrate of the electrode and is used to collect and transmit current.

[0027] (2) The active material layer contains active substances that can perform sodium ion insertion and extraction, which is the main body of the battery electrochemical reaction.

[0028] (3) The circuit breaking coating (functional layer) is the core component of this product. It is specifically placed between the current collector and the active material layer to form a physical interlayer.

[0029] The aforementioned circuit-breaking coating possesses both electrical conductivity and thermosensitive and / or piezoresistive volume expansion characteristics. These two properties, based on materials science response mechanisms, work synergistically to achieve intelligent control of the electrode's safety status. Firstly, regarding conductivity, based on normal operating conditions, the circuit-breaking coating acts as a bridge for electron transport during normal charge and discharge of the battery. It must possess sufficient conductivity to ensure that electrons can flow freely with low resistance between the current collector and the active material layer, thereby guaranteeing that the battery's power performance and capacity are not affected. This ensures that introducing this safety coating does not sacrifice the battery's conventional electrochemical performance.

[0030] Secondly, regarding volume expansion characteristics (based on abnormal response states), this coating material exhibits sensitive response capabilities to temperature changes (thermosensitive) or pressure changes (piezosensitive).

[0031] Specifically, the "thermosensitive" characteristic refers to the fact that when the internal temperature of the battery rises to a predetermined trigger temperature, the thermal motion of the molecular chains of the coating material (such as emerald green imine salt) intensifies, leading to an increase in the interchain spacing and expansion of the amorphous region, thereby achieving a physical circuit break.

[0032] Regarding the aforementioned "pressure-sensitive" characteristic, its circuit breaker response mechanism mainly includes two paths: Path 1 (Dominant Mechanism): Pressure-Induced Thermal Expansion. When a battery is subjected to external pressure or impact (i.e., the pressure reaches the predetermined trigger pressure), the deformation of the electrode under pressure is often accompanied by localized micro-short circuits or stress concentration generating heat. At this time, although the circuit-breaking coating is a response to the pressure, it essentially utilizes the localized temperature rise caused by the pressure to trigger the above-mentioned thermal expansion mechanism, thereby quickly cutting off the circuit before the pressure causes the separator to completely fail.

[0033] Pathway 2 (Auxiliary Mechanism): Structural Pressure-Sensitive Phase Transition. For certain specific circuit-breaking coating materials (such as specific polymer composite structures), when subjected to high pressure exceeding a predetermined threshold, their internal metastable structure may be destroyed or a pressure-induced phase transition may be induced, resulting in a sudden drop in material density, anomalous volume expansion, or the microcapsule structure pre-placed inside the coating may rupture under pressure and release an expansor, thereby achieving direct pressure-sensitive circuit breaking.

[0034] In summary, the "pressure-sensitive volume expansion characteristics" described in this application cover volume expansion directly caused by pressure, as well as volume expansion triggered by the thermal effect associated with pressure.

[0035] It should be noted that this expansion is not a minor thermal expansion and contraction, but a dramatic volume change that can produce a sufficient amount of displacement to overcome the adhesive force between the active material layer and the current collector.

[0036] In this embodiment, by setting two thresholds, "predetermined trigger temperature" and "predetermined trigger pressure," two distinct operating modes of the electrode are defined: First, the conduction mode (below the threshold): when the ambient temperature of the coating is lower than the predetermined trigger temperature and the pressure it is subjected to is lower than the predetermined trigger pressure (corresponding to normal battery operation, storage or slight disturbance), the volume of the disconnect coating remains stable, maintaining its function as a "conductive interface" and keeping the active material layer and the current collector tightly electrically connected.

[0037] Second, the open-circuit mode (above the threshold): When a short circuit occurs inside the battery, causing localized heating to reach the trigger temperature, or when the battery is subjected to external impact or compression, causing the coating to be pressured to reach the trigger pressure, the open-circuit coating is activated: In response, the coating rapidly expands in volume; the expanding coating generates enormous internal stress between the current collector and the active material layer, pushing the originally tightly attached active material layer outward, thereby causing the active material layer to physically separate or completely peel off from the current collector. Due to the interruption of physical contact, the electron transport path is cut off (i.e., the electrical connection is interrupted).

[0038] The "predetermined trigger temperature" can be understood as the critical point at which the coating material undergoes a phase transition or violent molecular motion. For example, this temperature is set before the melting temperature of the battery separator. Once a micro-short circuit is caused by a foreign object puncturing the membrane, generating heat, the coating immediately expands and breaks the circuit as soon as the temperature rises to this threshold, thereby cutting off the current before the separator fails and preventing thermal runaway.

[0039] The term "partial separation" does not require the complete detachment of the active material from the entire electrode sheet. In the case of a point short circuit (such as metal shavings penetrating the surface), only the coating around the short circuit point expands due to heat or pressure, causing the active material in that area to separate from the current collector, thus forming a "point break" that precisely isolates the fault point. Other areas of the electrode sheet may remain connected or break as heat diffuses.

[0040] In summary, in this embodiment, by providing a thermistor / varistor-sensitive circuit-breaking coating between the current collector and the active material layer, conductivity is maintained during normal battery operation. However, when encountering abnormal high temperatures or high pressures caused by an internal short circuit, the coating rapidly expands, causing the active layer to separate from the current collector and cutting off the electronic pathway. This mechanism effectively blocks short-circuit current, suppresses heat accumulation and thermal runaway chain reactions, solves safety hazards caused by manufacturing defects or mechanical abuse, and significantly improves the safety of sodium-ion batteries.

[0041] In some embodiments, the electrode is a sodium-ion battery positive electrode, the active material layer is a positive electrode active material layer, and the current collector is a positive electrode current collector.

[0042] The aforementioned positive current collector, serving as the electronic conductor substrate of the positive electrode, is typically made of materials such as aluminum foil and is responsible for collecting current. The aforementioned positive active material layer, attached above the current collector, contains compounds capable of reversibly extracting and inserting sodium ions. The aforementioned circuit-breaking coating, serving as a functional intermediate layer, is precisely positioned between the positive current collector and the positive active material layer.

[0043] Furthermore, the positive electrode active material in the positive electrode active material layer includes at least one of layered oxides, polyanionic materials, Prussian blue, and Prussian white.

[0044] Preferably, the compaction density of the sodium-ion battery positive electrode sheet is 1.5 g / cm³. 3 ~3.5g / cm 3 For example, it could be 1.5 g / cm³. 3 1.8g / cm 3 2.0g / cm 3 2.2g / cm 3 2.5g / cm 3 2.8g / cm 3 3.0g / cm 3 3.2g / cm 3 3.4g / cm 3 3.5g / cm 3 This range indicates that the breaking coating possesses sufficient mechanical strength and flexibility to withstand electrode compaction to 3.5 g / cm³. 3 The high-pressure rolling process ensures that the material does not crack or fail prematurely during manufacturing.

[0045] Within this density range, the active material particles are in close contact, which is beneficial for electron transport and increasing volumetric energy density. Under this high compaction density environment, the circuit-breaking coating can still maintain low internal resistance connection when in a "dormant" state, while under triggering conditions (overheating / overpressure), it has sufficient expansion force to overcome the interparticle adhesion after compaction, pushing the high-density active layer apart to achieve circuit breaking.

[0046] Furthermore, the positive electrode active material layer is a positive electrode active material layer formed by coating both sides of the positive electrode current collector, and the circuit breaking coating is disposed between the positive electrode current collector on each side and the corresponding positive electrode active material layer.

[0047] It should be noted that in this structure, the circuit-breaking coating covers both sides of the current collector. Regardless of which side of the electrode experiences an external impact or internal short circuit, or from which side a metallic foreign object penetrates, the corresponding circuit-breaking coating can respond independently or collaboratively. This "double-sided defense" design ensures comprehensive safety protection, effectively cutting off the electronic pathway on that side or both sides in the event of an abnormal trigger on either side.

[0048] In some embodiments, the electrode is a sodium-ion battery negative electrode, the active material layer is a negative electrode active material layer, and the current collector is a negative electrode current collector.

[0049] Furthermore, the negative electrode active material in the negative electrode active material layer includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, and graphene. Furthermore, the compaction density of the sodium-ion battery negative electrode sheet is 0.5 g / cm³. 3 ~1.5g / cm 3 For example, it could be 0.5 g / cm³. 3 0.6g / cm 3 0.7g / cm 3 0.8g / cm 3 0.9g / cm 3 1.0g / cm 3 1.1g / cm 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 .

[0050] The aforementioned range is significantly lower than that of the positive electrode sheet, consistent with the physical characteristics of carbon-based negative electrode materials (especially hard carbon) (typically low true density and requiring a certain porosity for electrolyte wetting). Lower compaction density implies a relatively loose or porous active material layer. In this structure, once the circuit-breaking coating expands due to abnormal operating conditions, the resulting expansion thrust more easily overcomes the interfacial bonding force between the active material layer and the current collector, thus more easily and quickly pushing away the negative electrode active layer, achieving efficient circuit breaking. This range indicates that the circuit-breaking coating can adapt to the pressure environment of the negative electrode rolling process, and will not exceed 0.5 g / cm³. 3 Poor contact due to low compaction will not occur at 1.5 g / cm. 3 Under relatively high pressure, it loses its expansion function.

[0051] It is important to note that introducing a circuit-breaking coating on the negative electrode side has special safety significance. The negative electrode is often a high-risk area for sodium deposition (formation of sodium dendrites). When external forces cause electrode deformation, or when internally grown dendrites / impurities pierce the separator and press against the negative electrode side, the circuit-breaking coating rapidly expands due to the induced pressure or localized heat generated by the short circuit, causing the negative electrode active layer to peel off from the current collector. This not only cuts off the electronic circuit but may also physically block the path for sodium dendrites to further grow into the current collector, thereby effectively preventing battery thermal runaway.

[0052] In some embodiments, the thickness of the circuit-breaking coating is not less than 10 μm. For example, it can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 18 μm, 19 μm, or 20 μm.

[0053] This thickness refers to the physical deposition thickness of the coating on the current collector. It ensures the coating has sufficient mass to produce significant volumetric expansion displacement. If it's too thin, the expansion may not be enough to completely disconnect the active layer from the current collector; if it's too thick, it may affect the battery's energy density. 10μm is a balance point, ensuring the effectiveness of safety functions.

[0054] In some embodiments, the coefficient of thermal expansion of the circuit-breaking coating is not less than 50 × 10⁻⁶. -6 K -1 .

[0055] In some embodiments, the volume expansion rate of the circuit-breaking coating is not less than 10%.

[0056] This embodiment provides the coating material's sensitivity to temperature changes (coefficient of thermal expansion) and its ability to change total volume under triggering conditions. A high coefficient of thermal expansion means that the molecular chain segments of the material move violently when heated, and the volume increases rapidly. A volume expansion rate of ≥10% ensures that the coating can generate sufficient thrust to "push" the active material layer away from the current collector surface and form a physical isolation zone when a short circuit occurs.

[0057] In some embodiments, the conductivity of the circuit-breaking coating is not less than 1.0 S / cm.

[0058] In some embodiments, the coating material forming the circuit-breaking coating is soluble in an organic solvent; preferably, the organic solvent includes at least one of N-methylpyrrolidone, dimethyl sulfoxide, cresol, and ethanol.

[0059] In some embodiments, the circuit-breaking coating comprises at least one of the following materials: carbon nanotube / polymer composite material, poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid, polyaniline, polypyrrole monomers or modified polymer materials, and metal / alloy foam materials.

[0060] It should be noted that when different material systems are used in the circuit-breaking coating, the microscopic mechanism of its volume expansion circuit breaking differs, but macroscopically, they all block the electronic pathway by disrupting the physical connection of the interface: (1) When polymer materials (such as emerald green imine salt) are used, physical separation is mainly achieved by the intensification of molecular chain vibration, the increase of spacing and the rapid volume expansion of amorphous regions at the trigger temperature.

[0061] (2) When metal / alloy foam materials (preferably shape memory alloy foam, or alloy foam with a high difference in thermal expansion coefficient) are used, the mechanism for achieving circuit breaking is not that the material itself transforms into an insulator, but rather relies on mechanical deformation. For example, when a short circuit in the battery causes local high temperature to reach the phase transformation trigger temperature of the alloy, the skeleton of the shape memory alloy foam will undergo a phase transformation from martensite to austenite, resulting in violent shape recovery or volume expansion (such as skeleton curling, springing open, or rapid expansion). At the same time, due to the significant difference in thermal expansion coefficient between the metal foam and the adjacent active material layer and current collector, this rapid deformation will generate huge interfacial shear stress and thrust, like a "jack" at the micro level, forcibly tearing and peeling the originally tightly attached active material layer and current collector. Due to the large-area detachment of the conductive interface and the forced breakage of physical contact, the micro and macro electronic pathways are completely cut off, thus achieving the safety protection effect of "expansion circuit breaking".

[0062] Furthermore, the circuit-breaking coating comprises an emerald green imine salt (ES) of polyaniline.

[0063] It should be noted that ES has a unique molecular structure (alternating phenylenediamine and quinone diimine units). When the temperature rises, the vibration and rotation of its molecular chains intensify, leading to increased interchain spacing and enhanced movement of amorphous chain segments, thus exhibiting significant macroscopic volume expansion characteristics, making it an ideal material for achieving "thermal circuit breaking".

[0064] Preferably, the circuit-breaking coating comprises emerald green imide salt, polytetrafluoroethylene (PTFE), and carbon nanotubes; preferably, the mass ratio of emerald green imide salt, PTFE, and carbon nanotubes is (7.0~9.0):(0.5~1.5):(0.5~1.5). The mass fraction of emerald green imide salt ranges from (7.0~9.0), for example, it can be 7.0 parts, 7.2 parts, 7.5 parts, 7.8 parts, 8.0 parts, 8.2 parts, 8.5 parts, 8.8 parts, or 9.0 parts. The mass fraction of PTFE ranges from (0.5~1.5), for example, it can be 0.5 parts, 0.6 parts, 0.8 parts, 1.0 parts, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, or 1.5 parts. The mass fraction of carbon nanotubes ranges from 0.5 to 1.5, for example, it can be 0.5 parts, 0.6 parts, 0.7 parts, 0.9 parts, 1.0 parts, 1.2 parts, 1.3 parts, 1.4 parts, or 1.5 parts.

[0065] Furthermore, the mass percentage W of the emerald green imine salt in the circuit-breaking coating satisfies: 70% ≤ W ≤ 90%. For example, it can be 70%, 72%, 75%, 78%, 80%, 82%, 85%, 87%, 89%, or 90%.

[0066] In some embodiments, the circuit-breaking coating is formed by at least one of the following methods: dip coating, hot pressing, particle deposition, chemical vapor deposition, physical vapor deposition, spin coating, plasma spraying, gravure coating, microgravure coating, and dispensing coating.

[0067] refer to Figure 1 This application also provides a method for preparing a sodium-ion battery electrode as described in any of the foregoing embodiments, comprising: Step S1: Apply a circuit breaking coating slurry to the surface of the current collector and perform a first drying process to form a circuit breaking coating on the surface of the current collector.

[0068] This step is the first step in electrode preparation. First, a liquid slurry containing a thermosensitive / pressure-sensitive expansion material (such as emerald green imine salt), a conductive agent, and a binder needs to be prepared. Then, this slurry is uniformly coated onto the surface of the current collector (usually aluminum foil) using a coating device. The subsequent "first drying treatment" refers to the evaporation and removal of solvents (such as NMP) from the slurry through methods such as heating or air drying.

[0069] This step is based on the principle of solvent evaporation film formation. The drying process causes the polymer materials and conductive agents in the slurry to solidify and cross-link, adhering tightly to the surface of the current collector to form a solid film with a specific thickness and physical strength. This step successfully constructs the core safety functional layer on the surface of the current collector. Forming a film on the current collector first ensures good physical contact and adhesion between the circuit breaker layer and the current collector, laying the foundation for normal electron transport and also providing a substrate for the coating of the next layer of active material.

[0070] Specifically, the coating method is not limited to a single form and can employ processes such as (but not limited to) dip coating and microgravure coating, flexibly selected according to the precision requirements of the production line and the viscosity of the slurry. Specifically, based on different film-forming principles, the formation methods are mainly divided into wet coating processes and dry deposition processes: The first category is wet coating processes, including dip coating, spin coating, plasma spraying, gravure coating, microgravure coating, and dispensing coating. These processes use a mixed slurry containing emerald green imine salts, polymer binders (such as polytetrafluoroethylene), and conductive agents (such as carbon nanotubes) as raw materials, which is cured into a film through solvent evaporation. Microgravure coating is particularly suitable for preparing thin, uniform (e.g., around 10 μm) break-circuit coatings.

[0071] The second category is dry deposition processes, including chemical vapor deposition (CVD) and physical vapor deposition (PVD). These processes do not use mixed slurries. For example, in CVD, aniline monomers can be directly used as a vapor-phase precursor to polymerize and deposit a polyaniline or its derivative coating in situ on the current collector surface; in PVD, a corresponding target is used for sputtering deposition. This method is suitable for preparing specific circuit-breaking coatings that do not contain binders or require extremely high coating purity.

[0072] Step S2: Apply an active material layer slurry to the surface of the circuit breaker coating and perform a second drying process to form an active material layer.

[0073] This step is a "layer coating" process. A slurry containing positive or negative electrode active materials is then applied over the dried and cured circuit-breaking coating.

[0074] The principle is to use a circuit-breaking coating as a "secondary current collector" or "intermediate substrate." The key to this step is to control the effect of the slurry solvent on the underlying circuit-breaking coating, preventing the underlying layer from re-dissolving or being damaged, ensuring a clear physical interface between the two layers while maintaining electrochemical connectivity. The second drying process is to remove the solvent from the active slurry.

[0075] Through stepwise coating and drying, a distinct sandwich structure of "current collector-breaking coating-active material layer" is ultimately formed on the electrode. This structure is the structural basis for achieving the breaking mechanism of "separation of the active material layer from the current collector." This results in an uncompacted electrode precursor with a double-layer coating structure.

[0076] Step S3: Roll the electrode sheet with the active material layer formed thereon to obtain the sodium-ion battery electrode sheet.

[0077] In this step, the dried multilayer composite electrode sheet is fed into a roller mill and subjected to enormous mechanical pressure for cold or hot pressing.

[0078] The principle behind this is that physical compression reduces the porosity between active material particles, increasing the compaction density of the coating. Rolling significantly reduces the electrode thickness and increases the volumetric energy density; the pressure forces the active particles to make closer contact with the circuit-breaking coating, and the circuit-breaking coating with the current collector, reducing the interfacial contact resistance (DCR); furthermore, this step also verifies the mechanical properties of the circuit-breaking coating, ensuring that the coating is sufficiently robust to withstand the high pressure of rolling without cracking or functional failure, thus guaranteeing that the finished electrode retains its safe circuit-breaking function after being assembled into the battery.

[0079] This step ultimately yields finished sodium-ion battery electrode sheets with uniform thickness, smooth surface, qualified density, and internal short-circuit protection.

[0080] In some embodiments, the drying conditions for the first drying treatment and / or the second drying treatment include: a temperature of 30°C to 120°C (e.g., 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C); and / or a wind frequency of 10Hz to 50Hz (e.g., 10Hz, 15Hz, 20Hz, 25Hz, 30Hz, 35Hz, 40Hz, 42Hz, 45Hz, 50Hz).

[0081] The temperature range described above covers processes ranging from slow drying at low temperatures to rapid drying at high temperatures. For solvents such as N-methylpyrrolidone (NMP) or water, sufficient heat is required for vaporization.

[0082] It should be noted that adjusting the airflow frequency is crucial. If the airflow is too high (high frequency), it may cause premature skin formation on the coating surface and internal solvent boiling, resulting in pinholes; if the airflow is too low (low frequency), the drying efficiency will be low, and the binder may float to the surface.

[0083] By combining temperature and airflow frequency (e.g., starting with low temperature and low airflow frequency, and ending with high temperature and high airflow frequency), "programmed temperature drying" was achieved. This ensures uniform curing of the coating from the inside out, preventing cracking or peeling. Furthermore, for circuit-breaking coatings containing heat-sensitive materials (such as emerald green imine salt), the upper limit is controlled at 120℃ to prevent premature thermal expansion or degradation of the material due to excessively high temperatures during preparation, thus ensuring the activity of the functional materials in the finished product.

[0084] In some embodiments, the coating speed of the active material layer slurry is 1 m / min to 45 m / min. For example, it can be 1 m / min, 5 m / min, 10 m / min, 15 m / min, 20 m / min, 25 m / min, 30 m / min, 35 m / min, 40 m / min, or 45 m / min.

[0085] It is important to note that the coating speed must be matched with the viscosity, solids content, and rheological properties of the slurry. Speed ​​control is crucial when applying a second coating to a substrate already coated with a circuit-breaking coating. Excessive speed can generate shear forces that may damage the underlying circuit-breaking coating; insufficient speed results in low production efficiency.

[0086] This speed range covers various scenarios from laboratory research and development (low-speed precision control) to pilot production or mass production (high-speed continuous production), indicating that the preparation process has good adaptability to production scale.

[0087] In some embodiments, the circuit breaking coating slurry is applied to the current collector surface by microgravure coating.

[0088] It should be noted that the circuit-breaking coating is typically quite thin (around 10 μm). Microgravure coating excels at achieving thin and uniform coatings with minimal thickness variation. This extremely high uniformity is a prerequisite for the circuit-breaking coating to function effectively. If the coating thickness is uneven, thinner areas may not completely interrupt the short-circuit current, while thicker areas may affect conductivity. The microgravure process ensures consistent safety performance throughout the entire electrode sheet.

[0089] This application also provides a circuit breaking coating slurry for forming the circuit breaking coating described in any of the foregoing embodiments. The circuit breaking coating slurry includes emerald green imine salt, polytetrafluoroethylene, carbon nanotubes, and the solvent N-methylpyrrolidone.

[0090] This embodiment provides a circuit-breaking coating slurry, which is a precursor mixture used to prepare a safety functional coating for sodium-ion batteries. It can be in the form of a liquid or colloidal suspension / solution. It is composed of functional solid particles, polymers, and solvents, and through coating and drying processes, is ultimately transformed into the solid circuit-breaking coating described in the aforementioned embodiment.

[0091] Further, the mass ratio of the emerald green imine salt, the polytetrafluoroethylene (PTFE), and the carbon nanotubes is (7.0~9.0):(0.5~1.5):(0.5~1.5). The mass fraction of the emerald green imine salt ranges from (7.0~9.0), for example, it can be 7.0 parts, 7.2 parts, 7.5 parts, 7.8 parts, 8.0 parts, 8.2 parts, 8.5 parts, 8.8 parts, or 9.0 parts. The mass fraction of the polytetrafluoroethylene ranges from (0.5~1.5), for example, it can be 0.5 parts, 0.6 parts, 0.8 parts, 1.0 parts, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, or 1.5 parts. The mass fraction of carbon nanotubes ranges from 0.5 to 1.5, for example, it can be 0.5 parts, 0.6 parts, 0.7 parts, 0.9 parts, 1.0 parts, 1.2 parts, 1.3 parts, 1.4 parts, or 1.5 parts.

[0092] Furthermore, the circuit breaker coating slurry is ultrasonically dispersed before coating.

[0093] This method utilizes the cavitation effect and high-frequency vibration generated by ultrasound in a liquid to break up the aggregation of nanomaterials (especially carbon nanotubes and polymer chains). Strong van der Waals forces exist between CNTs, making them prone to tangling. Ultrasonic treatment breaks them up, allowing for uniform distribution, thus achieving optimal conductivity with minimal quantity. Furthermore, it ensures uniform distribution of ES particles at the microscale, preventing "dead zones" in the coating (i.e., areas with only binder and no expansion material), guaranteeing that the final electrode can sensitively trigger a circuit break in any tiny area where a short circuit occurs.

[0094] This application also provides a sodium-ion battery, including a positive electrode, a negative electrode, and a separator; wherein at least one of the positive electrode and the negative electrode is a sodium-ion battery electrode as described in any of the foregoing embodiments.

[0095] The sodium-ion battery provided in this embodiment mainly consists of a positive electrode, a negative electrode, a separator separating the positive and negative electrodes, an electrolyte immersed in the separator, and an outer packaging shell. A key feature of this battery is that at least one of its positive or negative electrode employs a special electrode structure with the aforementioned thermistor / varistor-sensitive circuit-breaking function, thereby endowing the entire battery cell with self-protection capabilities against internal short circuits or external abuse. The form of this sodium-ion battery is not limited to a specific packaging method, and includes, but is not limited to, cylindrical batteries, prismatic hard-shell batteries, pouch batteries, and button batteries, making it suitable for various energy storage or power applications with high safety requirements.

[0096] This application also provides an electrical device, including a sodium-ion battery as described in the foregoing embodiments.

[0097] The electrical equipment provided in this application incorporates the aforementioned sodium-ion battery with high safety characteristics as a power source or energy storage unit. Thanks to the battery's significant advantages in preventing thermal runaway, the electrical equipment exhibits enhanced safety during operation. Such electrical equipment covers a wide range, including but not limited to: mobile communication devices (such as smartphones and walkie-talkies), portable electronic products (such as laptops, tablets, and digital cameras), wearable devices (such as smartwatches and VR glasses), electric vehicles (such as electric bicycles, electric motorcycles, electric balance scooters, and low-speed electric vehicles), energy storage power station systems (such as home energy storage cabinets and base station backup power supplies), and various power tools (such as electric drills and chainsaws).

[0098] The present invention will be further illustrated below with specific embodiments. However, it should be understood that these embodiments are merely for the purpose of more detailed illustration and should not be construed as limiting the present invention in any way.

[0099] Example 1 In this embodiment, the positive and negative electrode sheets are prepared.

[0100] While the embodiments of this application primarily demonstrate the preparation process using N-methylpyrrolidone (NMP) as a dispersing solvent, those skilled in the art should understand that the coating materials forming the circuit-breaking coating (especially emerald green imine salts and carbon nanotubes) can also achieve good dispersion or dissolution in other polar organic solvents.

[0101] For example, dimethyl sulfoxide (DMSO) and cresol have good solubility for polyaniline-based conductive polymers, enabling the formation of uniform film-forming solutions; while ethanol, as an environmentally friendly solvent, can also prepare satisfactory slurries when combined with appropriate dispersants or modified alcohol-soluble polyaniline / binder systems. Therefore, the scope of protection of this application should not be limited to NMP, but should cover any organic solvent system that can dissolve or disperse the coating material and dry it into a film.

[0102] The preparation method is as follows: 1. Preparation of positive electrode sheet: (1) Green imine salt (ES), polyvinylidene fluoride (PTFE) and conductive carbon nanotubes (CNT) were mixed in a mass ratio of 7.0:1.5:1.5. N-methylpyrrolidone (NMP) was added as a solvent and the mixture was ultrasonically dispersed. The slurry was then uniformly coated onto the surface of the positive current collector using a micro-gravure coating. After drying, the circuit-breaking coating with a thickness of 10 μm was obtained.

[0103] (2) The layered oxide of the positive electrode active material, conductive carbon black (SP) as a conductive agent, carbon nanotubes (CNT) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are mixed in a mass ratio of 95.5:1.8:1.2:1.5. N-methylpyrrolidone (NMP) is added as a solvent to form a positive electrode slurry with a theoretical solid content of 65%, and the mixture is stirred evenly. The positive electrode slurry is uniformly coated onto the surface of the circuit-breaking coating layer in step (1) by transfer coating. After drying, a positive electrode sheet with a single-sided coating of positive electrode active material is obtained. Then, the above coating steps are repeated on the other surface of the electrode sheet to obtain a positive electrode sheet with a double-sided coating of positive electrode active material. After coating, the positive electrode sheet is dried and rolled to achieve a compaction density of 3.0 g / cm³. 3 .

[0104] 2. Preparation of the negative electrode sheet: Hard carbon (negative electrode active material), conductive carbon black (SP) and carbon nanotubes (CNT) (conductive agent), SBR (single-phase binder), and carboxymethyl cellulose (CMC) (dispersant) were mixed in a mass ratio of 93.6:1.5:1.0:2.5:1.4. Deionized water was then added as a solvent to prepare a negative electrode slurry with a theoretical solid content of 33%. The mixture was stirred evenly and then uniformly coated onto the surface of a 12 μm thick aluminum foil used for negative electrode current collectors. After drying, a negative electrode sheet with a single-sided coating of the negative electrode active material layer was obtained. The above steps were repeated on the other side of the negative electrode sheet to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. After coating, the negative electrode sheet was dried and rolled. The compacted (rolled) density of the negative electrode sheet was 0.9 g / cm³.

[0105] Example 2 In this embodiment, the positive and negative electrode sheets are prepared. The preparation method is as follows: 1. Preparation of positive electrode sheet: (1) Green imine salt (ES), polyvinylidene fluoride (PTFE) and conductive carbon nanotubes (CNT) were mixed in a mass ratio of 7.5:1.5:1.0. N-methylpyrrolidone (NMP) was added as a solvent. After ultrasonic dispersion, the slurry was uniformly coated on the surface of the positive current collector by microgravure coating. After drying, the circuit breaking coating with a thickness of 10 μm was obtained.

[0106] (2) The layered oxide of the positive electrode active material, conductive carbon black (SP) as a conductive agent, carbon nanotubes (CNT) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are mixed in a mass ratio of 95.5:1.8:1.2:1.5. N-methylpyrrolidone (NMP) is added as a solvent to form a positive electrode slurry with a theoretical solid content of 65%, and the mixture is stirred evenly. The positive electrode slurry is uniformly coated onto the surface of the circuit-breaking coating layer in step (1) by transfer coating. After drying, a positive electrode sheet with a single-sided coating of positive electrode active material is obtained. Then, the above coating steps are repeated on the other surface of the electrode sheet to obtain a positive electrode sheet with a double-sided coating of positive electrode active material. After coating, the positive electrode sheet is dried and rolled to achieve a compaction density of 3.0 g / cm³. 3 .

[0107] 2. Preparation of the negative electrode sheet: Hard carbon (negative electrode active material), conductive carbon black (SP) and carbon nanotubes (CNT) (conductive agent), SBR (single-phase binder), and carboxymethyl cellulose (CMC) (dispersant) were mixed in a mass ratio of 93.6:1.5:1.0:2.5:1.4. Deionized water was then added as a solvent to prepare a negative electrode slurry with a theoretical solid content of 33%. The mixture was stirred evenly and then uniformly coated onto the surface of a 12 μm thick aluminum foil used for negative electrode current collectors. After drying, a negative electrode sheet with a single-sided coating of the negative electrode active material layer was obtained. The above steps were repeated on the other side of the same negative electrode sheet to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. After coating, the negative electrode sheet was dried and rolled. The compacted (rolled) density of the negative electrode sheet was 0.9 g / cm³. 3 .

[0108] Example 3 In this embodiment, the positive and negative electrode sheets are prepared. The preparation method is as follows: 1. Preparation of positive electrode sheet: (1) Green imine salt (ES), polyvinylidene fluoride (PTFE) and conductive carbon nanotubes (CNT) were mixed in a mass ratio of 8.0:1.0:1.0. N-methylpyrrolidone (NMP) was added as a solvent and the mixture was ultrasonically dispersed. The slurry was then uniformly coated onto the surface of the positive current collector using a micro-gravure coating. After drying, the circuit-breaking coating with a thickness of 10 μm was obtained.

[0109] (2) The layered oxide of the positive electrode active material, conductive carbon black (SP) as a conductive agent, carbon nanotubes (CNT) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are mixed in a mass ratio of 95.5:1.8:1.2:1.5. N-methylpyrrolidone (NMP) is added as a solvent to form a positive electrode slurry with a theoretical solid content of 65%, and the mixture is stirred evenly. The positive electrode slurry is uniformly coated onto the surface of the circuit-breaking coating layer in step (1) by transfer coating. After drying, a positive electrode sheet with a single-sided coating of positive electrode active material is obtained. Then, the above coating steps are repeated on the other surface of the electrode sheet to obtain a positive electrode sheet with a double-sided coating of positive electrode active material. After coating, the positive electrode sheet is dried and rolled to achieve a compaction density of 3.0 g / cm³. 3 .

[0110] 2. Preparation of the negative electrode sheet: Hard carbon (negative electrode active material), conductive carbon black (SP) and carbon nanotubes (CNT) (conductive agent), SBR (single-phase binder), and carboxymethyl cellulose (CMC) (dispersant) were mixed in a mass ratio of 93.6:1.5:1.0:2.5:1.4. Deionized water was then added as a solvent to prepare a negative electrode slurry with a theoretical solid content of 33%. The mixture was stirred evenly and then uniformly coated onto the surface of a 12 μm thick aluminum foil used for negative electrode current collectors. After drying, a negative electrode sheet with a single-sided coating of the negative electrode active material layer was obtained. The above steps were repeated on the other side of the same negative electrode sheet to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. After coating, the negative electrode sheet was dried and rolled. The compacted (rolled) density of the negative electrode sheet was 0.9 g / cm³. 3 .

[0111] Example 4 In this embodiment, the positive and negative electrode sheets are prepared. The preparation method is as follows: 1. Preparation of positive electrode sheet: (1) Green imine salt (ES), polyvinylidene fluoride (PTFE) and conductive carbon nanotubes (CNT) were mixed in a mass ratio of 8.5:1.0:0.5. N-methylpyrrolidone (NMP) was added as a solvent. After ultrasonic dispersion, the slurry was uniformly coated on the surface of the positive electrode current collector by microgravure coating. After drying, the circuit breaking coating with a thickness of 10 μm was obtained.

[0112] (2) The positive electrode active material layered oxide, conductive agent conductive carbon black (SP), conductive agent carbon nanotubes (CNT), and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95.5:1.8:1.2:1.5, and N-methylpyrrolidone (NMP) is added as a solvent to form a positive electrode slurry with a theoretical solid content of 65%, and stirred evenly. The positive electrode slurry is uniformly coated on the surface of the circuit-breaking coating in step (1) by transfer coating, and dried to obtain a positive electrode sheet with a single-sided coating of positive electrode active material. Then, the above coating steps are repeated on the other surface of the electrode sheet to obtain a positive electrode sheet with a double-sided coating of positive electrode active material. After coating, the positive electrode sheet is dried and rolled, and the compaction density of the positive electrode sheet is 3.0 g / cm3.

[0113] 2. Preparation of the negative electrode sheet: Hard carbon (negative electrode active material), conductive carbon black (SP) and carbon nanotubes (CNT) (conductive agent), SBR (single-phase binder), and carboxymethyl cellulose (CMC) (dispersant) were mixed in a mass ratio of 93.6:1.5:1.0:2.5:1.4. Deionized water was then added as a solvent to prepare a negative electrode slurry with a theoretical solid content of 33%. The mixture was stirred evenly and then uniformly coated onto the surface of a 12 μm thick aluminum foil used for negative electrode current collectors. After drying, a negative electrode sheet with a single-sided coating of the negative electrode active material layer was obtained. The above steps were repeated on the other side of the same negative electrode sheet to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. After coating, the negative electrode sheet was dried and rolled. The compacted (rolled) density of the negative electrode sheet was 0.9 g / cm³. 3 .

[0114] Example 5 In this embodiment, the positive and negative electrode sheets are prepared. The preparation method is as follows: 1. Preparation of positive electrode sheet: (1) Green imine salt (ES), polyvinylidene fluoride (PTFE) and conductive carbon nanotubes (CNT) were mixed in a mass ratio of 9.0:0.5:0.5. N-methylpyrrolidone (NMP) was added as a solvent and the mixture was ultrasonically dispersed. The slurry was then uniformly coated onto the surface of the positive current collector using a micro-gravure coating. After drying, the circuit-breaking coating with a thickness of 10 μm was obtained.

[0115] (2) The layered oxide of the positive electrode active material, conductive carbon black (SP) as a conductive agent, carbon nanotubes (CNT) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are mixed in a mass ratio of 95.5:1.8:1.2:1.5. N-methylpyrrolidone (NMP) is added as a solvent to form a positive electrode slurry with a theoretical solid content of 65%, and the mixture is stirred evenly. The positive electrode slurry is uniformly coated onto the surface of the circuit-breaking coating layer in step (1) by transfer coating. After drying, a positive electrode sheet with a single-sided coating of positive electrode active material is obtained. Then, the above coating steps are repeated on the other surface of the electrode sheet to obtain a positive electrode sheet with a double-sided coating of positive electrode active material. After coating, the positive electrode sheet is dried and rolled to achieve a compaction density of 3.0 g / cm³. 3 .

[0116] 2. Preparation of the negative electrode sheet: Hard carbon (negative electrode active material), conductive carbon black (SP) (conductive agent), carbon nanotubes (CNT) (conductive agent), SBR (single-phase binder), and carboxymethyl cellulose (CMC) (dispersant) were mixed in a mass ratio of 93.6:1.5:1.0:2.5:1.4. Deionized water was added as a solvent to prepare a negative electrode slurry with a theoretical solid content of 33%. The mixture was stirred evenly and then uniformly coated onto the surface of a 12 μm thick aluminum foil used for negative electrode current collectors using a transfer coating method. After drying, a negative electrode sheet with a single-sided coating of the negative electrode active material layer was obtained. The above steps were repeated on the other side of the same negative electrode sheet to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. After coating, the negative electrode sheet was dried and rolled. The compacted (rolled) density of the negative electrode sheet was 0.9 g / cm³. 3 .

[0117] Comparative Example 1 In this comparative example, positive and negative electrode sheets were prepared. The preparation method is as follows: 1. Preparation of positive electrode sheet: (1) 100% emerald green imine salt (ES) was added to N-methylpyrrolidone (NMP) as a solvent. After being ultrasonically dispersed evenly, the slurry was uniformly coated on the surface of the positive electrode current collector by micro-gravure coating. After drying, the circuit-breaking coating with a thickness of 10 μm was obtained.

[0118] (2) The layered oxide of the positive electrode active material, conductive carbon black (SP) as a conductive agent, carbon nanotubes (CNT) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are mixed in a mass ratio of 95.5:1.8:1.2:1.5. N-methylpyrrolidone (NMP) is added as a solvent to form a positive electrode slurry with a theoretical solid content of 65%, and the mixture is stirred evenly. The positive electrode slurry is uniformly coated onto the surface of the circuit-breaking coating layer in step (1) by transfer coating. After drying, a positive electrode sheet with a single-sided coating of positive electrode active material is obtained. Then, the above coating steps are repeated on the other surface of the electrode sheet to obtain a positive electrode sheet with a double-sided coating of positive electrode active material. After coating, the positive electrode sheet is dried and rolled to achieve a compaction density of 3.0 g / cm³. 3 .

[0119] 2. Preparation of the negative electrode sheet: Hard carbon (negative electrode active material), conductive carbon black (SP) and carbon nanotubes (CNT) (conductive agent), SBR (single-phase binder), and carboxymethyl cellulose (CMC) (dispersant) were mixed in a mass ratio of 93.6:1.5:1.0:2.5:1.4. Deionized water was then added as a solvent to prepare a negative electrode slurry with a theoretical solid content of 33%. The mixture was stirred evenly and then uniformly coated onto the surface of a 12 μm thick aluminum foil used for negative electrode current collectors. After drying, a negative electrode sheet with a single-sided coating of the negative electrode active material layer was obtained. The above steps were repeated on the other side of the same negative electrode sheet to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. After coating, the negative electrode sheet was dried and rolled. The compacted (rolled) density of the negative electrode sheet was 0.9 g / cm³. 3 .

[0120] Comparative Example 2 In this comparative example, positive and negative electrode sheets were prepared. The preparation method is as follows: 1. Preparation of positive electrode sheet: A mixture of layered oxide as the positive electrode active material, conductive carbon black (SP) as a conductive agent, carbon nanotubes (CNT) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder was prepared in a mass ratio of 95.5:1.8:1.2:1.5. N-methylpyrrolidone (NMP) was added as a solvent to form a positive electrode slurry with a theoretical solid content of 65%, and the mixture was stirred until homogeneous. The positive electrode slurry was then uniformly coated onto the surface of a 12 μm thick aluminum foil used as a positive electrode current collector via transfer coating. After drying, a positive electrode sheet with a single-sided coating of the positive electrode active material was obtained. The coating process was then repeated on the other side of the positive electrode sheet to obtain a positive electrode sheet with a double-sided coating of the positive electrode active material. After coating, the positive electrode sheet was dried and rolled to achieve a compaction density of 3.0 g / cm³. 3 .

[0121] 2. Preparation of the negative electrode sheet: Hard carbon (negative electrode active material), conductive carbon black (SP) and carbon nanotubes (CNT) (conductive agent), SBR (single-phase binder), and carboxymethyl cellulose (CMC) (dispersant) were mixed in a mass ratio of 93.6:1.5:1.0:2.5:1.4. Deionized water was then added as a solvent to prepare a negative electrode slurry with a theoretical solid content of 33%. The mixture was stirred evenly and then uniformly coated onto the surface of a 12 μm thick aluminum foil used for negative electrode current collectors. After drying, a negative electrode sheet with a single-sided coating of the negative electrode active material layer was obtained. The above steps were repeated on the other side of the same negative electrode sheet to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. After coating, the negative electrode sheet was dried and rolled. The compacted (rolled) density of the negative electrode sheet was 0.9 g / cm³. 3 .

[0122] Comparative Example 3 The only difference between this comparative example and Example 1 is that, in step (1), the amount of adhesive applied by the microgravure coating is controlled so that the thickness of the broken-circuit coating after drying is 5 μm. The rest of the preparation process and testing conditions are the same as those in Example 1.

[0123] The main differences between the above embodiments and comparative examples can be found in Table 1: Table 1. Comparison of some key parameters in the examples and comparative examples.

[0124] In Table 1, ES represents emerald green imine salt (thermosensitive expansion material); PTFE represents polyvinylidene fluoride; CNT represents carbon nanotubes (conductive agent); " / " indicates that the item does not exist or is not applicable.

[0125] Test Experiment 1. Testing method: (1) Test of coating thickness during circuit breaking: 1) Micrometer measurement: Current collector thickness: T1; Current collector + circuit breaker coating thickness: T2; Circuit breaker coating thickness = T2 - T1.

[0126] 2) Using SEM technology, the thickness of different coating sections of the electrode is tested based on the different morphologies of each component.

[0127] (2) Cyclic performance test: At room temperature (25°C), the sodium-ion battery was charged to 3.8V under 1C constant current and constant voltage conditions, and then discharged to 1.5V under 1C constant current conditions.

[0128] (3) Ratio performance test: At room temperature, discharge at 0.5C to 1.5V and rest for 30 minutes; discharge at 0.5C to 3.8V, cut off at 0.05C and rest for 30 minutes; discharge at 0.5C / 1C / 2C / 5C to 1.5V and rest for 30 minutes; discharge at 0.5C to 1.5V and rest for 30 minutes; charge at 0.5C / 1C / 2C / 5CCC to 3.8V, cut off at 0.05C and rest for 30 minutes; discharge at 0.5CCC to 1.5V and rest for 30 minutes.

[0129] (4) DCR test: Adjust the 0.5C discharge to 90% / 80% / 70% / 60% / 50% / 40% / 30% / 20% / 10% SOC, let stand for 5 minutes, and then charge at 1C for 30 seconds.

[0130] (5) Short circuit test: A nickel sheet is placed inside, and compression causes an internal short circuit. Observe for 1 hour to confirm whether the battery cell smokes, catches fire, or explodes.

[0131] (2) Coating conductivity test: The sheet resistance of the prepared open circuit coating surface is tested using a four-probe resistance tester (e.g., RTS-9 type), and the conductivity of the coating (S / cm) is calculated based on the coating thickness.

[0132] 2. Test Results and Analysis: Table 2. Performance Test Results

[0133] Table 3. Coating Conductivity

[0134] Analysis: The following conclusions can be drawn from the comparison of the data in Tables 2 and 3: (1) Safety verification of the circuit breaking coating (Examples 1-5 vs Comparative Example 2): Compared with Comparative Example 2 without circuit breaking coating (smoke and fire occurred), all Examples 1-5 and Comparative Example 1 with circuit breaking coating passed the internal short circuit test (no smoke or fire).

[0135] It is important to note that the "compression-induced internal short circuit" method used in this test is actually a comprehensive verification of the "varistor-sensitive triggering" and "thermal response" of the circuit-breaking coating. When the cell is subjected to external compressive pressure (simulating varistor-sensitive triggering conditions), the electrode deforms, leading to localized micro-short circuits and heat generation (simulating thermal triggering conditions). The excellent performance of Examples 1-5 demonstrates that whether the structural changes are directly induced by pressure or the localized temperature rise caused by pressure, the circuit-breaking coating can respond rapidly and expand to break the circuit. This verifies the effectiveness of the "thermal and / or varistor" characteristics described in the aforementioned examples under actual abuse conditions.

[0136] This fully demonstrates that the introduction of the circuit-breaking coating can significantly reduce the risk of short circuits within the battery cell. The mechanism is that the emerald green imine salt (ES) in the coating expands in volume when heated (as shown in Table 1, the expansion amount is 1.98μm~4.62μm at 100℃), physically isolating the short circuit point from the current collector, thereby cutting off the electronic pathway.

[0137] (2) Overall advantages of the composite formulation (Examples 1-5 vs. Comparative Example 1): Although Comparative Example 1 (100% ES) showed good safety and the largest expansion (4.62 μm), it suffered from severe "excessive powder shedding" and its internal resistance (ACR 34.67 mΩ, DCR 46.11 mΩ) was significantly higher than that of the other examples. This indicates that although pure ES material has good expansion performance, it has poor film-forming properties and lower conductivity than the composite material.

[0138] In contrast, Examples 1-5, by introducing polytetrafluoroethylene (PTFE) and carbon nanotubes (CNTs), significantly improved the coating appearance (no powder shedding or only slight powder shedding) and reduced the battery internal resistance (ACR / DCR was close to that of the uncoated Comparative Example 2) while maintaining excellent safety performance. This demonstrates the synergistic effect of the binder enhancing structural stability and the conductive agent constructing a highly efficient conductive network.

[0139] (3) Verification of the coefficient of thermal expansion: In the embodiments of this application, the coefficient of thermal expansion of the circuit-breaking coating is limited to not less than 50×10. -6 K -1 According to the test data of Example 1 in Table 2, the thickness increase of the coating at 100℃ is 1.98μm. Assuming the test reference temperature is room temperature (25℃), the temperature difference ΔT = 75℃, and the initial thickness L0 = 10μm, the following calculations are made using the thermal expansion formula α = ΔL / (L0 × ΔT): α = 1.98 / (10 × 75) = 0.00264 K - ¹ = 2640 × 10 -6 K - ¹.

[0140] The calculation result (2640 × 10) -6 K -1 The value is much larger than the lower limit (50×10) specified in the aforementioned embodiments. -6 K -1 This fully demonstrates that the circuit-breaking coating prepared in the embodiments of this application has extremely high thermal response characteristics, which is sufficient to meet the design requirements.

[0141] (4) Basis for optimizing the component ratio: Data shows that as the ES ratio increases from 70% to 90% (Examples 1 to 5), the thermal expansion capacity of the coating gradually increases (from 1.98μm to 3.86μm), which is more conducive to circuit breaking. However, when the ES ratio reaches 90% (Example 5), a "slight powder shedding" phenomenon begins to appear; when it reaches 100% (Comparative Example 1), a "large amount of powder shedding" occurs.

[0142] To further investigate the optimal content range of the core component, emerald green imine salt (ES), in the circuit-breaking coating, the data in Table 2 were plotted as follows: Figure 2 and Figure 3 Conduct trend analysis.

[0143] like Figure 2 As shown, as the mass percentage of ES in the breaking coating gradually increases from 70% to 100%, the increase in coating thickness (expansion rate) after heating at 100°C exhibits a clear linear growth trend, increasing from 1.98 μm in Example 1 to 4.62 μm in Comparative Example 1. This confirms that the higher the ES content, the stronger the thermal breaking response capability.

[0144] However, Figure 2 The inflection point of process stability was also revealed: when the ES content was in the range of 70% to 85%, the coating surface was dense and "did not shed powder"; when the ES content reached 90% (Example 5), "slight powder shedding" began to occur; and when the ES content reached 100% (Comparative Example 1), "a large amount of powder shedding" occurred. This indicates that excessively high ES content will lead to a relative lack of binder, seriously damaging the structural integrity of the coating.

[0145] On the other hand, such as Figure 3 As shown, regarding the impact on electrical performance, the ACR and DCR bar heights of Comparative Example 1 (100% ES) were significantly higher than those of other groups, indicating that the pure ES coating would significantly increase the battery's internal resistance. Conversely, the internal resistance bar heights of Examples 1-5 (ES content 70%-90%, and compounded with CNT and PTFE) were basically the same as those of Comparative Example 2 (no coating), indicating that within this formulation range, the hindering effect of the coating on electron transport was successfully suppressed.

[0146] comprehensive Figure 2 Regarding the balance between expansion and powder shedding, and Figure 3 Regarding the analysis of internal resistance, this application determined that 70% to 90% is the optimal mass ratio of emerald green imine salt (ES). Within this range, the electrode can achieve sufficient thermal expansion breaking capacity (thickness increment ≥ 1.98 μm) while maintaining good coating structure stability and excellent conductivity.

[0147] (5) Comparing Example 1 (thickness 10 μm, expansion 1.98 μm, no smoke) with Comparative Example 3 (thickness 5 μm, expansion 0.98 μm, slight smoke), it can be seen that the initial thickness of the circuit-breaking coating directly determines its absolute expansion displacement after heating. When the coating is too thin (e.g., 5 μm), even if the expansion rate (%) of the material itself remains unchanged, the resulting absolute displacement (approximately 1 μm) is insufficient to completely overcome the interfacial adhesion between the active material layer and the current collector, or the formed isolation gap is insufficient to completely block electron transitions under high voltage, resulting in incomplete circuit breaking and thus posing a safety hazard. Therefore, it is essential that this application limits the thickness of the circuit-breaking coating to not less than 10 μm.

[0148] In summary, to achieve the best balance between safety due to expansion and coating processing stability (no powder shedding) / conductivity, it is recommended to control the mass percentage of emerald green imine salt (ES) in the circuit breaking coating between 70% and 90%, and the coating thickness not less than 10 μm, to ensure sufficient circuit breaking displacement.

[0149] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sodium-ion battery electrode, characterized in that, It includes a current collector, an active material layer, and a circuit-breaking coating disposed between the current collector and the active material layer; The circuit-breaking coating is a conductive coating and has thermosensitive and / or piezoresistive volume expansion characteristics. When the temperature of the circuit-breaking coating is lower than the predetermined trigger temperature and / or the pressure on the circuit-breaking coating is lower than the predetermined trigger pressure, the circuit-breaking coating remains conductive, so that the active material layer is electrically connected to the current collector; When the temperature of the circuit-breaking coating reaches or exceeds the predetermined trigger temperature and / or the pressure on the circuit-breaking coating reaches or exceeds the predetermined trigger pressure, the circuit-breaking coating can undergo volume expansion, causing the active material layer to separate from the current collector at least partially, thereby interrupting the electrical connection between the active material layer and the current collector.

2. The sodium-ion battery electrode as described in claim 1, characterized in that, The electrode is a sodium-ion battery positive electrode, the active material layer is a positive electrode active material layer, and the current collector is a positive electrode current collector; Preferably, the positive electrode active material in the positive electrode active material layer includes at least one of layered oxide, polyanionic material, Prussian blue, and Prussian white; Preferably, the compaction density of the sodium-ion battery positive electrode sheet is 1.5 g / cm³. 3 ~3.5g / cm 3 ; Preferably, the positive electrode active material layer is a positive electrode active material layer formed by coating both sides of the positive electrode current collector, and the circuit breaking coating is disposed between the positive electrode current collector on each side and the corresponding positive electrode active material layer.

3. The sodium-ion battery electrode as described in claim 1, characterized in that, The electrode is a sodium-ion battery negative electrode, the active material layer is a negative electrode active material layer, and the current collector is a negative electrode current collector; Preferably, the negative electrode active material in the negative electrode active material layer includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, and graphene; Preferably, the compaction density of the sodium-ion battery negative electrode sheet is 0.5 g / cm³. 3 ~1.5g / cm 3 .

4. The sodium-ion battery electrode as described in claim 1, characterized in that, The thickness of the circuit-breaking coating is not less than 10 μm; and / or, The coefficient of thermal expansion of the circuit-breaking coating is not less than 50 × 10⁻⁶. -6 K -1 ; and / or, The volume expansion rate of the circuit-breaking coating is not less than 10%; and / or, The conductivity of the circuit-breaking coating is not less than 1.0 S / cm; and / or, The coating material forming the circuit-breaking coating is soluble in an organic solvent; preferably, the organic solvent includes at least one selected from N-methylpyrrolidone, dimethyl sulfoxide, cresol, and ethanol; and / or, The circuit-breaking coating is formed by at least one of the following methods: dip coating, hot pressing, particle deposition, chemical vapor deposition, physical vapor deposition, spin coating, plasma spraying, gravure coating, microgravure coating, and dispensing coating.

5. The sodium-ion battery electrode as described in claim 1, characterized in that, The circuit-breaking coating includes at least one of the following materials: carbon nanotube / polymer composite material, poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid, polyaniline, polypyrrole monomers or modified polymer materials, and metal / alloy foam materials. Preferably, the circuit-breaking coating comprises a turquoise imine salt of polyaniline; Preferably, the circuit-breaking coating comprises emerald green imine salt, polytetrafluoroethylene, and carbon nanotubes; preferably, the mass ratio of emerald green imine salt, polytetrafluoroethylene, and carbon nanotubes is (7.0~9.0):(0.5~1.5):(0.5~1.5); preferably, the mass percentage W of emerald green imine salt in the circuit-breaking coating satisfies: 70%≤W≤90%.

6. A method for preparing a sodium-ion battery electrode as described in any one of claims 1-5, characterized in that, include: A circuit breaking coating slurry is applied to the surface of the current collector and a first drying process is performed to form a circuit breaking coating on the surface of the current collector. An active material layer slurry is coated onto the surface of the circuit-breaking coating and then subjected to a second drying process to form an active material layer. The electrode sheet with the active material layer formed thereon is rolled to obtain the sodium-ion battery electrode sheet.

7. The method for preparing the sodium-ion battery electrode as described in claim 6, characterized in that, The drying conditions for the first drying treatment and / or the second drying treatment include: a temperature of 30°C to 120°C; and / or a wind frequency of 10Hz to 50Hz; and / or... The coating speed of the active material layer slurry is 1 m / min to 45 m / min; and / or, The circuit breaking coating slurry is applied to the surface of the current collector by microgravure coating.

8. A circuit-breaking coating slurry, characterized in that, For forming the circuit breaking coating according to any one of claims 1-5, the circuit breaking coating slurry comprises emerald green imine salt, polytetrafluoroethylene, carbon nanotubes and solvent N-methylpyrrolidone; Preferably, the mass ratio of the emerald green imine salt, the polytetrafluoroethylene, and the carbon nanotubes is (7.0~9.0):(0.5~1.5):(0.5~1.5). Preferably, the circuit breaker coating slurry is ultrasonically dispersed before coating.

9. A sodium-ion battery, characterized in that, Includes positive electrode, negative electrode, and separator; Wherein, at least one of the positive electrode and the negative electrode is a sodium-ion battery electrode as described in any one of claims 1-5.

10. An electrical appliance, characterized in that, Including the sodium-ion battery as described in claim 9.

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