Sodium ion secondary battery with multi-cavity packaging structure and thermal runaway protection method thereof

Abstract

The invention discloses a sodium ion secondary battery with a multi-cavity packaging structure and a thermal runaway protection method thereof, the sodium ion secondary battery comprises a main cavity, a thermal runaway pressure relief channel arranged on one side of the main cavity and a composite protection layer arranged on the outer wall of the main cavity, and the thermal runaway pressure relief channel is filled with a phase change material and a fire extinguishing medium storage bag. The auxiliary cavities are respectively four peripheral sub-cavities and one central sub-cavity, and an independent sodium ion battery cell unit is packaged in each peripheral sub-cavity and each central sub-cavity. The internal temperature of each sub-cavity is monitored through a temperature sensor, an electric isolation module is triggered to cut off a circuit of the sub-cavity, meanwhile, perfluorohexanone gas in a fire extinguishing medium storage bag is released, and a basalt fiber woven layer is activated to be unfolded to form cooling fins. A four-stage thermal runaway protection system is constructed through multi-cavity physical isolation, thermal diffusion delaying of a double-layer thermal insulation layer, cooperative fire control of a phase change material and a fire extinguishing agent, dynamic heat dissipation of a composite protection layer and active response of intelligent sensing and shape memory alloy.

Description

Technical Field

[0001] The present invention relates to the technical field of battery protection, and in particular to a sodium ion secondary battery with a multi-cavity packaging structure and a thermal runaway protection method thereof. Background Art

[0002] With the acceleration of global energy transformation, sodium-ion secondary batteries have shown broad application prospects in large-scale energy storage, low-speed electric vehicles and other fields due to their advantages such as abundant sodium resources, low cost and environmental friendliness. However, during the charging and discharging process, existing sodium-ion batteries are prone to local overheating or even thermal runaway due to the volume change of electrode materials, the thermal stability limitation of electrolytes and the heat dissipation requirements brought about by the increase in energy density, leading to battery short circuit, fire or explosion. The traditional single-cavity packaging structure has problems such as uneven heat conduction and rapid spread of thermal runaway, and the thermal insulation layer is mostly made of a single material with limited protective performance. At the same time, the existing thermal management system lacks independent monitoring and precise intervention of each battery unit, the release efficiency of the fire extinguishing medium is low, and the heat dissipation structure is difficult to respond quickly after thermal runaway, which seriously affects the safety and reliability of the battery. In addition, the structural stability of the positive electrode materials (such as layered oxides) of sodium-ion batteries at high voltages and the compatibility of the electrolyte further exacerbate the risk of battery failure. Summary of the Invention

[0003] In order to overcome the deficiencies of the existing technical solutions, the present invention provides a sodium ion secondary battery with a multi-cavity packaging structure, which can effectively solve the problems raised by the background technology.

[0004] The technical solution adopted by the present invention to solve its technical problem is:

[0005] A sodium-ion secondary battery with a multi-cavity packaging structure comprises a main cavity, a thermal runaway pressure relief channel provided on one side of the main cavity, and a composite protective layer provided on the outer wall of the main cavity. The thermal runaway pressure relief channel is filled with a phase change material and a fire extinguishing medium storage capsule. The composite protective layer comprises, from the inside to the outside, a silicon carbide coating, a basalt fiber braided layer, and a polyimide film. The main cavity comprises an outer shell made of a highly thermally conductive metal material. The interior of the main cavity is divided into at least three mutually independent sub-cavities. The main cavity is also provided with a double-layer thermal insulation layer and a honeycomb support structure for connecting the sub-cavities.

[0006] The sub-cavities are respectively composed of 4 peripheral sub-cavities and 1 central sub-cavity, the peripheral sub-cavities are arranged in a ring array, and adjacent peripheral sub-cavities are physically isolated by a double-layer thermal insulation layer, and the double-layer thermal insulation layer includes an aerogel inner layer and a ceramic fiber outer layer;

[0007] Each of the peripheral sub-cavity and the central sub-cavity is encapsulated with an independent sodium ion battery cell unit, and each battery cell unit is connected to the integrated electrode on the top of the main cavity through a parallel circuit.

[0008] As a further description of the above technical solution, the diameter of the central sub-cavity is larger than the diameter of the peripheral sub-cavity, and the central sub-cavity and the peripheral sub-cavity are connected by a honeycomb support structure, and a temperature sensor and a gas concentration detector are provided on the surface of the support structure.

[0009] As a further description of the above technical solution, the thickness of the aerogel inner layer is 0.5-1.2 mm, and the surface of the ceramic fiber outer layer is provided with a micron-level concave-convex texture with a concave-convex depth of 50-200 μm and a texture coverage area ≥85%.

[0010] A method for protecting a sodium ion secondary battery from thermal runaway in a multi-cavity packaging structure comprises the following steps:

[0011] Step S1: The temperature inside each sub-cavity is monitored in real time by a temperature sensor. When it is detected that the temperature of a sub-cavity exceeds a threshold value T1, the electrical isolation module is triggered to cut off the circuit of the sub-cavity;

[0012] Step S2: Within 0.5-2 seconds after the circuit is cut off, the phase change material in the thermal runaway pressure relief channel is activated to absorb heat, and the perfluorohexanone gas in the fire extinguishing medium storage capsule is released at the same time;

[0013] Step S3: After confirming the termination of thermal runaway through the gas concentration detector, the basalt fiber braided layer of the composite protective layer on the outer wall of the main cavity is activated to unfold to form heat dissipation fins.

[0014] As a further description of the above technical solution, the release pressure of the fire extinguishing medium storage bag in step S2 is 0.8-1.5 MPa, and when released, atomized spray is formed through the microchannel, and the atomized particle size is controlled within the range of 10-50 μm.

[0015] As a further description of the above technical solution, the positive electrode material of the sodium ion battery cell is a layered oxide Na_x[Ni_yMn_zCo_w]O2, where 0.6≤x≤0.8, and y:z:w=1:1:1, the negative electrode uses hard carbon material, and the electrolyte contains a 1MNaPF6 EC / DMC mixed solution (volume ratio 3:7) and 2wt% of fluoroethylene carbonate additive.

[0016] As a further description of the above technical solution, the cell pore size of the honeycomb support structure is 2-5 mm, the porosity is ≥70%, and each cell is embedded with a shape memory alloy wire, which deforms when the temperature exceeds 80°C, reducing the pore size by 20%-40%.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The sodium ion secondary battery with a multi-cavity packaging structure and the thermal runaway protection method thereof of the present invention have at least one of the following beneficial effects during use:

[0019] With the development of renewable energy storage and electrification technologies, sodium-ion secondary batteries have great potential in large-scale energy storage and low-end power fields due to their abundant sodium resources and low cost. However, existing sodium-ion batteries face severe challenges: thermal runaway is easily caused by heat accumulation during charging and discharging, leading to safety accidents such as short circuits and fires; traditional single-cavity packaging structures have problems with uneven heat conduction and rapid spread of thermal runaway, and the protective performance of single thermal insulation materials is limited; the thermal management system lacks accurate monitoring and intervention of independent battery cells, the release efficiency of fire extinguishing media is low, and the heat dissipation response is delayed after thermal runaway. At the same time, the structural stability of layered oxide positive electrode materials and electrolyte compatibility issues further increase the risk of battery failure. Therefore, there is an urgent need for a sodium-ion battery packaging structure with independent protection of multiple cavities and efficient thermal management capabilities to solve the core pain points of insufficient safety and low thermal management efficiency in existing technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the overall structure of a sodium ion secondary battery with a multi-cavity packaging structure according to the present invention;

[0021] Figure 2 This is a schematic diagram of the first side structure of a sodium ion secondary battery with a multi-cavity packaging structure according to the present invention;

[0022] Figure 3 This is a schematic diagram of the second side structure of a sodium ion secondary battery with a multi-cavity packaging structure according to the present invention.

[0023] Numbers in the figure:

[0024] 1. Main cavity; 101. Double-layer insulation layer; 102. Fire extinguishing medium storage capsule; 103. Honeycomb support structure; 104. Temperature sensor; 105. Integrated electrode; 106. Gas concentration detector; 2. Sub-cavity; 201. Peripheral sub-cavity; 202. Sodium ion battery cell unit; 203. Central sub-cavity. DETAILED DESCRIPTION

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0026] like Figure 1-3As shown, the present invention provides a sodium-ion secondary battery with a multi-cavity packaging structure, including a main cavity 1, a thermal runaway pressure relief channel provided on one side of the main cavity 1, and a composite protective layer provided on the outer wall of the main cavity 1, wherein the thermal runaway pressure relief channel is filled with a phase change material and a fire extinguishing medium storage capsule 102, and the composite protective layer includes a silicon carbide coating, a basalt fiber braided layer, and a polyimide film arranged in sequence from the inside to the outside, the main cavity 1 is made of an outer shell made of a high thermal conductivity metal material, and the interior of the main cavity 1 is divided into at least three independent sub-cavities 2, and the main cavity 1 is further provided with a double-layer thermal insulation layer 101 and a honeycomb support structure 103 for connecting the sub-cavities 2.

[0027] The main cavity 1 structure of this embodiment is composed of a high thermal conductivity metal shell, which is divided into four peripheral sub-cavities 201 and one central sub-cavity 203 in a ring array layout. The double-layer thermal insulation layer 101 is an aerogel inner layer (0.5-1.2mm) and a ceramic fiber outer layer (with a micron-level concave-convex texture on the surface). The thermal runaway pressure relief channel is filled with phase change material and perfluorohexanone fire extinguishing medium storage capsule 102. The composite protective layer adopts silicon carbide coating (inner layer for impact resistance), basalt fiber braided layer (middle layer for thermal insulation) and polyimide film (outer layer for insulation).

[0028] The secondary cavity 2 is composed of four peripheral sub-cavities 201 and one central sub-cavity 203. The peripheral sub-cavities 201 are arranged in a circular array. Adjacent peripheral sub-cavities 201 are physically isolated by a double-layer insulation layer 101. The double-layer insulation layer 101 includes an aerogel inner layer and a ceramic fiber outer layer.

[0029] The battery system is divided into multiple independent cavities, limiting the spread of thermal runaway through physical isolation. The central sub-cavity 203 has a larger diameter and can preferentially withstand the stress caused by thermal expansion. The circular arrangement of the peripheral sub-cavities 201 optimizes the heat dissipation path. When heat diffuses from the center to the periphery, it is blocked by the double-layer insulation layer 101, reducing the thermal conduction efficiency (the thermal conductivity of the aerogel is as low as 0.02W / m·K, and the ceramic fiber reflects thermal radiation).

[0030] Each of the peripheral sub-cavity 201 and the central sub-cavity 203 is encapsulated with an independent sodium ion battery cell unit 202 , and each battery cell unit is connected to the integrated electrode 105 on the top of the main cavity 1 through a parallel circuit.

[0031] Each sub-chamber houses an independent sodium-ion battery cell, and the parallel circuit design ensures that a single cell failure does not affect the overall power supply. Phase-change materials (such as paraffin or metal-organic frameworks) absorb heat and undergo a phase transition (solid-to-liquid) during thermal runaway, slowing the rate of temperature rise. After the perfluorohexanone storage capsule ruptures due to heat, it is atomized and sprayed through microchannels (particle size 10-50μm), rapidly covering the fire source and suppressing the combustion chain reaction.

[0032] The silicon carbide coating protects against external mechanical impact, preventing the housing from rupturing and potentially causing a secondary short circuit. The basalt fiber braid acts as a thermal barrier under normal conditions, but upon activation, it unfolds into heat sink fins, increasing surface area and improving heat dissipation efficiency (the fins expand and increase the heat dissipation area by 30%-50%). The polyimide film withstands high temperatures (>400°C) and maintains insulation, preventing electrochemical corrosion caused by the external environment.

[0033] It is further explained that the diameter of the central sub-cavity 203 is larger than the diameter of the peripheral sub-cavity 201, and the central sub-cavity 203 and the peripheral sub-cavity 201 are connected by a honeycomb support structure 103, and a temperature sensor 104 and a gas concentration detector 106 are provided on the surface of the support structure.

[0034] The hexagonal cells of the honeycomb structure (pore size 2-5mm, porosity ≥70%) provide high specific strength and disperse the mechanical stress generated during thermal runaway. The high porosity allows gas to circulate, accelerating the diffusion of heat from the center to the periphery; the shape memory alloy wire shrinks when the temperature is greater than 80°C (such as Ni-Ti alloy), and the pore size is reduced by 20%-40%, which limits the oxygen supply and suppresses combustion. Temperature sensor 104 (such as NTC thermistor): monitors the temperature of each sub-cavity in real time, and the threshold T1 is set to 80-100°C (lower than the flash point of the electrolyte). Gas concentration detector 106 (such as electrochemical sensor): detects thermal runaway characteristic gases such as CO and H2, and shuts down the fire extinguishing system after confirming that the thermal runaway has ended.

[0035] The honeycomb support structure 103 connects the sub-cavities 2. Its cell pore size is 2-5mm, and its porosity is ≥70%. This structural design ensures sufficient support strength while facilitating the flow of gas and heat. Each cell is embedded with a shape-memory alloy wire. When the temperature exceeds 80°C, the alloy wire deforms, reducing the pore size by 20%-40%, thereby controlling the flow of heat and gas and providing a barrier against thermal runaway.

[0036] It is further explained that the thickness of the aerogel inner layer is 0.5-1.2 mm, and the surface of the ceramic fiber outer layer is provided with a micron-level concave-convex texture with a concave-convex depth of 50-200 μm and a texture coverage area ≥85%.

[0037] The inner layer of aerogel is 0.5-1.2mm thick, and the outer layer of ceramic fiber has a micron-scale concave-convex texture (depth 50-200μm, coverage ≥85%). The nanoporous structure (porosity >90%) achieves ultra-low thermal conductivity (0.016-0.025W / m·K) by limiting air convection and solid heat conduction, delaying heat transfer to adjacent cavities. The thickness of 0.5-1.2mm balances thermal insulation performance and space occupation (too thin is easy to break down, too thick increases volume).

[0038] A method for protecting a sodium ion secondary battery from thermal runaway in a multi-cavity packaging structure comprises the following steps:

[0039] Step S1: The temperature sensor 104 monitors the internal temperature of each sub-cavity in real time. When it is detected that the temperature of a sub-cavity exceeds the threshold value T1, the electrical isolation module is triggered to cut off the circuit of the sub-cavity.

[0040] The internal temperature of each sub-cavity is monitored in real time by temperature sensors 104 installed on the surface of the honeycomb support structure 103. When the temperature of a sub-cavity exceeds the threshold value T1, it indicates that the sub-cavity may be experiencing thermal runaway. At this time, the electrical isolation module is triggered to disconnect the circuit of the sub-cavity, preventing the faulty sub-cavity from affecting the circuits of other sub-cavities and preventing further expansion of thermal runaway.

[0041] Within 0.5-2 seconds after the circuit is disconnected, the phase change material in the thermal runaway pressure relief channel activates to absorb heat, utilizing the latent heat of the phase change material to absorb heat and reduce the temperature within the sub-cavity. Simultaneously, the fire extinguishing medium storage capsule 102, under a release pressure of 0.8-1.5 MPa, forms an atomized spray through the microchannels. The atomized particle size is controlled within the range of 10-50 μm, evenly distributing the perfluorohexanone gas in the form of fine droplets in the thermal runaway area, improving fire extinguishing efficiency and rapidly extinguishing the fire.

[0042] After the gas concentration detector 106 confirms that the thermal runaway has terminated, that is, it detects that the gas concentration generated by the fire has dropped to a safe range, the basalt fiber woven layer of the composite protective layer on the outer wall of the main cavity 1 is activated and expanded to form heat dissipation fins, thereby increasing the heat exchange area between the battery and the outside world, accelerating the dissipation of residual heat, and allowing the battery to return to normal operating temperature as soon as possible.

[0043] Step S2: Within 0.5-2 seconds after the circuit is cut off, the phase change material in the thermal runaway pressure relief channel is activated to absorb heat, and the perfluorohexanone gas in the fire extinguishing medium storage capsule 102 is released at the same time;

[0044] Step S3: After the gas concentration detector 106 confirms that the thermal runaway has terminated, the basalt fiber braided layer of the composite protective layer on the outer wall of the main cavity 1 is activated to unfold to form heat dissipation fins.

[0045] The main chamber 1 is constructed from a highly thermally conductive metal shell, which rapidly conducts heat generated within the battery, preventing excessive heat accumulation. Its interior is divided into four peripheral sub-cavities 201 and one central sub-cavity 203. The peripheral sub-cavities 201 are arranged in a circular array, while the central sub-cavity 203 has a larger diameter than the peripheral sub-cavities 201. The two sub-cavities are connected by a honeycomb support structure 103. Each sub-cavity houses independent sodium-ion battery cells 202, which are connected to the integrated electrode 105 at the top of the main chamber 1 via a parallel circuit, enabling the collection and output of electrical energy. Adjacent peripheral sub-cavities 201 are physically isolated by a double-layer insulation layer 101, consisting of an inner aerogel layer and an outer ceramic fiber layer. The inner aerogel layer has extremely low thermal conductivity, effectively preventing heat transfer between adjacent sub-cavities. The outer ceramic fiber layer, with its excellent high-temperature resistance, further enhances the insulation, creating a double layer of thermal insulation protection.

[0046] The composite protective layer, from inside to outside, consists of a silicon carbide coating, a basalt fiber braid, and a polyimide film. The silicon carbide coating, with its high hardness and strong wear resistance, protects the main cavity 1 from mechanical impact and chemical corrosion. The basalt fiber braid adheres tightly to the main cavity 1 under normal conditions. Once thermal runaway ceases, it can unfold under specific conditions to form heat dissipation fins, increasing the heat dissipation area and accelerating heat dissipation. The polyimide film has excellent high-temperature resistance and insulation properties, protecting the internal structure from high temperatures and electrical interference.

[0047] The thermal runaway pressure relief channel is filled with phase change material and a fire extinguishing medium storage capsule 102. When the battery experiences thermal runaway and the temperature rises to its phase transition temperature, the phase change material absorbs a large amount of heat and undergoes a phase change, thereby lowering the local temperature and absorbing heat. The fire extinguishing medium storage capsule 102 stores perfluorohexanone gas. In the event of thermal runaway, the storage capsule ruptures and releases the gas to extinguish the fire.

[0048] It is further explained that the release pressure of the fire extinguishing medium storage capsule 102 in step S2 is 0.8-1.5 MPa, and when released, atomized spray is formed through the microchannel, and the atomized particle size is controlled within the range of 10-50 μm.

[0049] The positive electrode material of the sodium ion battery cell 202 is a layered oxide Na_x[Ni_yMn_zCo_w]O2, where 0.6≤x≤0.8, and y:z:w=1:1:1, the negative electrode uses a hard carbon material, and the electrolyte contains a 1MNaPF6 EC / DMC mixed solution (volume ratio 3:7) and 2wt% of fluoroethylene carbonate additive.

[0050] The Ni / Mn / Co ratio is 1:1:1, balancing capacity and structural stability (Ni provides capacity, Mn / Co inhibits phase transition), high specific capacity (300mAh / g) and low sodium insertion potential (<0.1Vvs.Na / Na + ), improve energy density, fluoroethylene carbonate (FEC) forms a dense SEI film (containing NaF) on the surface of the negative electrode, inhibiting the decomposition of the electrolyte and gas production.

[0051] It is further explained that the cell pore size of the honeycomb support structure 103 is 2-5 mm, the porosity is ≥70%, and each cell is embedded with a shape memory alloy wire, which deforms when the temperature exceeds 80°C, causing the pore size to shrink by 20%-40%.

[0052] Ni-Ti alloy wire undergoes austenite transformation at 80°C, generating shrinkage stress (strain 4%-8%), reducing the honeycomb aperture, and restricting the oxygen diffusion path (oxygen flow rate is reduced by 30%-50%).

[0053] A four-level thermal runaway protection system is constructed through multi-cavity physical isolation, double-layer insulation layer 101 to delay heat diffusion, coordinated fire control of phase change materials and fire extinguishing agents, dynamic heat dissipation of composite protective layers, and active response of intelligent sensors and shape memory alloys.

[0054] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A sodium ion secondary battery with a multi-cavity packaging structure, characterized in that: The device comprises a main cavity, a thermal runaway pressure relief channel provided on one side of the main cavity, and a composite protective layer provided on the outer wall of the main cavity. The thermal runaway pressure relief channel is filled with a phase change material and a fire extinguishing medium storage capsule. The composite protective layer comprises, from the inside to the outside, a silicon carbide coating, a basalt fiber braided layer, and a polyimide film. The main cavity is outer-cased in a highly thermally conductive metal material. The interior of the main cavity is divided into at least three mutually independent sub-cavities. The main cavity is also provided with a double-layer thermal insulation layer and a honeycomb support structure for connecting the sub-cavities. The sub-cavities are respectively composed of 4 peripheral sub-cavities and 1 central sub-cavity, the peripheral sub-cavities are arranged in a ring array, and adjacent peripheral sub-cavities are physically isolated by a double-layer thermal insulation layer, and the double-layer thermal insulation layer includes an aerogel inner layer and a ceramic fiber outer layer; Each of the peripheral sub-cavity and the central sub-cavity is encapsulated with an independent sodium ion battery cell unit, and each battery cell unit is connected to the integrated electrode on the top of the main cavity through a parallel circuit.

2. The sodium ion secondary battery with a multi-cavity packaging structure according to claim 1, characterized in that: The diameter of the central sub-cavity is greater than that of the peripheral sub-cavity, and the central sub-cavity and the peripheral sub-cavity are connected by a honeycomb support structure, and a temperature sensor and a gas concentration detector are provided on the surface of the support structure.

3. The sodium ion secondary battery with a multi-cavity packaging structure according to claim 1, characterized in that: The thickness of the aerogel inner layer is 0.5-1.2 mm, and the surface of the ceramic fiber outer layer is provided with micron-level concave-convex texture, the concave-convex depth is 50-200 μm, and the texture coverage area is ≥85%.

4. The thermal runaway protection method for a sodium ion secondary battery with a multi-cavity packaging structure according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step S1: The temperature inside each sub-cavity is monitored in real time by a temperature sensor. When it is detected that the temperature of a sub-cavity exceeds a threshold value T1, the electrical isolation module is triggered to cut off the circuit of the sub-cavity; Step S2: Within 0.5-2 seconds after the circuit is cut off, the phase change material in the thermal runaway pressure relief channel is activated to absorb heat, and the perfluorohexanone gas in the fire extinguishing medium storage capsule is released at the same time; Step S3: After confirming the termination of thermal runaway through the gas concentration detector, the basalt fiber braided layer of the composite protective layer on the outer wall of the main cavity is activated to unfold to form heat dissipation fins.

5. The thermal runaway protection method for a sodium ion secondary battery with a multi-cavity packaging structure according to claim 4, characterized in that: The release pressure of the fire extinguishing medium storage bag in step S2 is 0.8-1.5 MPa. When released, atomized spray is formed through the microchannel, and the atomized particle size is controlled within the range of 10-50 μm.

6. The sodium ion secondary battery with a multi-cavity packaging structure according to claim 1, characterized in that: The positive electrode material of the sodium ion battery cell is a layered oxide Na_x[Ni_yMn_zCo_w]O2, where 0.6≤x≤0.8 and y:z:w=1:1:1, the negative electrode uses a hard carbon material, and the electrolyte contains a 1MNaPF6 EC / DMC mixed solution (volume ratio 3:7) and 2wt% of fluoroethylene carbonate additive.

7. The sodium ion secondary battery with a multi-cavity packaging structure according to claim 1, characterized in that: The cell pore size of the honeycomb support structure is 2-5 mm, the porosity is ≥70%, and each cell is embedded with a shape memory alloy wire. When the temperature exceeds 80° C., the alloy wire deforms to reduce the pore size by 20%-40%.

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