Method for improving direct lithiation efficiency

Abstract

The invention discloses a method for improving direct lithiation efficiency. Comprising the following steps: (1) mixing an active substance with a pre-lithiation reagent, then adding a binder and a conductive agent, fiberizing the binder through high-speed mixing, and then pressing the fiberized material into a film through high-temperature rolling to achieve the purpose of pre-lithiation; and (2) rolling the membrane obtained in the step (1) through a differential roller at different roller speed ratios, so that the active substance and the pre-lithiation reagent further form an alloy phase, the physicochemical degree is improved, and finally, the obtained membrane and a current collector are compounded to form the dry-method electrode plate, so that the final physicochemical purpose is achieved. On one hand, the pre-lithiation reagent is added in the material high-speed mixing process, the pre-lithiation reagent is uniformly distributed on the surface of the active substance while the binder is fiberized, and the pre-lithiation uniformity is improved; and on the other hand, different shear forces generated by different roller speed ratios of the differential roller are utilized to apply different pressures between the lithiation reagent and the silicon material to induce contact points to form a lithium-silicon alloy, so that the purpose of efficient pre-lithiation is achieved.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a method for improving direct lithiation efficiency. Background Technology

[0002] Silicon (Si)-based anodes are considered one of the most promising materials for next-generation lithium-ion batteries (LIBs) due to their theoretical capacity being approximately 10 times that of traditional graphite anodes. However, silicon-based anodes suffer from low initial coulombic efficiency (ICE) during early cycling due to the formation of the solid electrolyte interface (SEI) and the irreversible lithiation of the active silicon-based material. To improve the ICE of silicon-based anodes, pre-lithiation technology has become an increasingly popular research topic.

[0003] Direct contact pre-lithiation technology involves physical contact between lithium metal and the electrode, utilizing the self-discharge of lithium metal to achieve pre-lithiation. This method is simple and can achieve deep lithiation. Patent CN 119581491 A, by directly covering the electrode surface with lithium foil for lithium replenishment, suffers from incomplete contact between the lithium foil and the electrode surface, leading to reduced lithiation efficiency. Patent CN119419214 A adds inert lithium powder during material mixing, which can achieve uniform lithiation, but its utilization rate of the lithium source is low, resulting in low lithiation efficiency. To improve lithiation efficiency, different pressures can be applied to the electrode to increase the diffusion rate of lithium ions and induce lithiation. Under pressure, electrons in the lithium metal near the contact point between the pre-lithiation reagent and the negative electrode active material can migrate to silicon under the influence of the electric field formed by the potential difference between lithium and silicon, achieving physicochemical transformation. However, traditional pressure induction uses a hydraulic press to apply pressure to the electrode. This method requires the electrode to be prepared before it can be carried out, which increases the preparation process and reduces production efficiency. In addition, due to the limited area of ​​the hydraulic platform of the hydraulic press, the area of ​​electrode lithiation induced in a single operation is small, and it is impossible to continuously apply pressure to induce electrode lithiation, which reduces the lithiation efficiency. Therefore, how to find an efficient, continuous and simple method for inducing lithiation has become an urgent problem for those skilled in the art.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] To address the problem of low lithium source utilization and consequently low lithiation efficiency in existing technologies, this invention provides a method for improving direct lithiation efficiency. This invention involves mixing a negative electrode active material, a pre-lithiation reagent, a binder, and a conductive agent to form a fibrous material, which is then rolled into a film. This film is then rolled using a differential roller, utilizing the shear pressure generated between the two rollers to induce pre-lithiation. Using a differential roller to roll the pre-lithiated electrode has two advantages: firstly, the shear pressure between the two rollers better promotes the deformation of lithium metal, improving its physical contact with the silicon negative electrode material, thereby increasing the diffusion rate and improving lithiation efficiency; secondly, using a differential roller allows for continuous shear pressure to be applied to the electrode, achieving continuous pre-lithiation and improving production efficiency.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for improving direct lithiation efficiency includes the following steps: (1) Mixing: The negative electrode active material and the pre-lithiation reagent are pre-mixed using a degassing machine to obtain the pre-lithiation material. A conductive agent and a fiberizable binder are added to the pre-lithiation material and mixed at high speed to obtain the fiberized material. (2) Film formation: The fibrous material obtained in step (1) is rolled into a film by a roller press; (3) Induced lithiation: The film obtained in step (2) is rolled by a differential roller press at different differential speed ratios; (4) Coating: The membrane obtained in step (3) is laminated onto the copper current collector by hot rolling to obtain the negative electrode.

[0007] Furthermore, the negative electrode active material in step (1) includes any one or at least two combinations of nano-silicon materials, porous silicon, silicon-based composite materials, silicon oxide (SiOx), silicon alloys (Si-Fe, Si-Ni, etc.), core-shell structured silicon, three-dimensional structured silicon, and other novel structures.

[0008] Furthermore, the pre-lithiation reagent is any one or more of the following: lithium metal reagents (lithium foil, lithium powder, lithium strip), lithium compounds (such as Li2O, Li3N, Li2CO3), organic lithium reagents (LiPAA, LiTFSI, lithium-ionized polymers), composite pre-lithiation reagents (lithium / carbon composite, lithium / silicon composite), and in-situ lithium source additives (LiF, Li2S, LiNO3). By adding the pre-lithiation reagent during the high-speed mixing of materials, the pre-lithiation reagent is uniformly distributed on the surface of the active material while the binder is fibrous, thereby improving the uniformity of pre-lithiation.

[0009] Furthermore, the conductive agent includes any one or more of single-walled carbon nanotubes, multi-arm carbon nanotubes, conductive carbon black, carbon fibers, or graphene.

[0010] Furthermore, the fiberizable adhesive includes one or more of the following: thermoplastic polymeric adhesives (PTFE, PVDF modified materials), conductive polymeric adhesives (PEDOT:PSS, polyaniline-based materials), composite fiberizable adhesives (PTFE / carbon nanotube composites, bio-based cellulose / synthetic polymer composites), elastic adhesives (SEBS, polyurethane-based materials), and low-melting-point adhesives (modified polyethylene, polypropylene derivatives).

[0011] Furthermore, in step (1), the pre-lithiation reagent accounts for 0.5 wt%-6 wt% of the negative electrode active material.

[0012] Furthermore, in step (1), the pre-lithiated material, conductive agent and fiberizable binder are mixed in different proportions, wherein the conductive agent and fiberizable binder account for 0.5wt%-2wt% of the pre-lithiated material, the high-speed mixing speed is 600-1600rpm, and the high-speed mixing time is 10-60min.

[0013] Furthermore, in step (2), the temperature of the roller press is controlled at 60-150℃ and the pressure is 0.5-5t.

[0014] Furthermore, in step (3), the roller temperature of the differential roller press is 110-150℃, the differential speed ratio of the two rollers is 0.5-5 and not 1, preferably 2-4, and the shear pressure generated between the two rollers induces pre-lithiation. By utilizing different roller speed ratios to generate different shear forces, different pressures are applied between the lithiation reagent and the silicon material to induce the formation of a lithium-silicon alloy at their contact points, thereby achieving the purpose of efficient pre-lithiation.

[0015] Furthermore, the hot roller pressing temperature in step (4) is 110-150℃ and the pressure is 0.5-5t.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: (1) In view of the problems existing in the prior art, the present invention provides a method to improve the direct lithiation efficiency. Under pressure, electrons in lithium metal near the contact position between the pre-lithiation reagent and the negative electrode active material can migrate to silicon under the action of the electric field formed by the potential difference between lithium and silicon to achieve physicochemical transformation.

[0017] (2) In this invention, a negative electrode active material, a pre-lithiation reagent, a binder, and a conductive agent are mixed to form a fibrous material, which is then rolled into a film. The film is then rolled by a differential speed roller, and the shear pressure generated between the two rollers is used to induce pre-lithiation. On the one hand, the pre-lithiation reagent is added during the high-speed mixing of the material. While the binder is fibrous, the pre-lithiation reagent is evenly distributed on the surface of the active material, improving the uniformity of pre-lithiation. On the other hand, the different shear forces generated by the different roller speed ratios of the differential speed rollers apply different pressures to the contact points between the lithiation reagent and the silicon material, inducing the formation of a lithium-silicon alloy, thereby achieving the purpose of efficient pre-lithiation. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the differential speed roller pressing the diaphragm. Figure 2 This is a picture of the mixture after mixing in Example 1; Figure 3 This is a picture of the differential roller after pressing in Example 1; Figure 4 The first coulombic efficiency curves for the assembled half-cell tests of Example 1 and Comparative Example 1 are shown.

[0020] In the diagram, 1 is differential roller A, 2 is differential roller B, and 3 is the film formed by roller pressing. Detailed Implementation

[0021] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be obtained by practicing the invention. It will be understood by those skilled in the art that the detailed description is merely illustrative and should not be construed as a specific limitation thereof.

[0022] The embodiments of the present invention do not particularly limit the method of induced lithiation. Any similar induced lithiation method can be used in this application without departing from the inventive concept. As one embodiment, the induced lithiation method includes, but is not limited to, one or more of the following: hot pressing treatment, mechanical stress-controlled lithium diffusion, and pressure-temperature combined control.

[0023] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0024] Example 1 A method for improving direct lithiation efficiency includes the following steps: (1) Silicon-oxygen 450 (SiO) 450 The pre-lithiation material is obtained by mixing the pre-lithiation reagent, inert lithium powder (SLMP), with the inert lithium powder (SLMP) accounting for 450% of the negative electrode active material, silicon oxide (SiO2). 450 3 wt% of the pre-lithiated material was added, followed by 1 wt% of conductive carbon black (SP) and 1.5 wt% of fiberizable binder (PTFE). The mixture was stirred at 1000 rpm for 30 min to obtain the fiberized material. (2) The fibrous material obtained in step (1) is rolled into a film by a roller press. The roller press temperature is 85℃ and the pressure is 2t. The film is then calendered into a dry film. (3) The dry film obtained in step (2) is passed through a differential roller press. The speed of roller A is 4 rpm, the speed of roller B is 1 rpm, the differential speed ratio of the two rollers is 4, and the temperature is 120℃. (4) The diaphragm obtained by differential roller press in step (3) is combined with the current collector and hot roller press to coat the film to obtain the negative electrode sheet. The hot roller pressing temperature is 120℃ and the pressure is 2t.

[0025] Example 2 The difference between Example 2 and Example 1 is that in step (3), the speed ratio of the differential roller is 5, the speed of roller A is 5 rpm, and the speed of roller B is 1 rpm.

[0026] Example 3 The difference between Example 3 and Example 1 is that in step (3), the speed ratio of the differential roller is 3, the speed of roller A is 3 rpm, and the speed of roller B is 1 rpm.

[0027] Example 4 The difference between Example 4 and Example 1 is that in step (3), the speed ratio of the differential roller is 2, the speed of roller A is 2 rpm, and the speed of roller B is 1 rpm.

[0028] Example 5 The difference between Example 5 and Example 1 is that in step (3), the speed ratio of the differential roller is 0.5, the speed of roller A is 0.5 rpm, and the speed of roller B is 1 rpm.

[0029] Example 6 The difference between Example 6 and Example 1 is that the proportion of the pre-lithiation reagent in step (1) is 2%.

[0030] Example 7 The difference between Example 7 and Example 1 is that the proportion of the pre-lithiation reagent in step (1) is 4%.

[0031] Example 8 The difference between Example 8 and Example 1 is that the proportion of the pre-lithiation reagent in step (1) is 5%.

[0032] Example 9 The method for improving direct lithiation efficiency in this embodiment includes the following steps: (1) Silicon-oxygen 450 (SiO) 450 The pre-lithiation material is obtained by mixing the pre-lithiation reagent with inert lithium powder (SLMP). The pre-lithiation reagent accounts for 3 wt% of the negative electrode active material. Then, conductive carbon black (SP) accounting for 0.5 wt% of the pre-lithiation material and fiberizable binder (PTFE) accounting for 1.5 wt% of the pre-lithiation material are added. The mixture is stirred at 1500 rpm for 20 min to obtain the fiberized material. (2) The fibrous material obtained in step (1) is rolled into a film by a roller press. The roller press temperature is 85℃ and the pressure is 2t. The film is then calendered into a dry film. (3) The dry film obtained in step (2) is passed through a differential roller press. The speed of roller A is 4 rpm, the speed of roller B is 1 rpm, the differential speed ratio of the two rollers is 4, and the temperature is 120℃. (4) The membrane obtained in step (3) and the current collector are hot rolled together by a roller press to obtain a negative electrode sheet. The hot rolling temperature is 120℃ and the pressure is 1t.

[0033] Example 10 The method for improving direct lithiation efficiency in this embodiment includes the following steps: (1) Silicon-Carb 450 (SiC) 450 The pre-lithiation material is obtained by mixing the pre-lithiation reagent with inert lithium powder (SLMP). The pre-lithiation reagent accounts for 3 wt% of the negative electrode active material. Then, conductive carbon black (SP) accounting for 1.5 wt% of the pre-lithiation material and fiberizable binder (PTFE) accounting for 1 wt% of the pre-lithiation material are added. The mixture is stirred at 800 rpm for 15 min to obtain the fiberized material. (2) The fibrous material obtained in step (1) is rolled into a film by a roller press. The roller press temperature is 85℃ and the pressure is 2t. The film is then calendered into a dry film. (3) The dry film obtained in step (2) is passed through a differential roller press. The speed of roller A is 4 rpm, the speed of roller B is 1 rpm, the differential speed ratio of the two rollers is 4, and the temperature is 120℃. (4) The membrane obtained in step (3) is coated together with the current collector through a roller press to obtain a negative electrode sheet. The hot roller pressing temperature is 120℃ and the pressure is 0.5t.

[0034] Example 11 The method for improving direct lithiation efficiency in this embodiment includes the following steps: (1) Silicon-oxygen-carbon 450 (SiOC) 450 The pre-lithiation material is obtained by mixing the pre-lithiation reagent with inert lithium powder (SLMP). The pre-lithiation reagent accounts for 3 wt% of the negative electrode active material. Then, conductive carbon black (SP) accounting for 2 wt% of the pre-lithiation material and fiberizable binder (PVDF) accounting for 1 wt% of the pre-lithiation material are added. The mixture is stirred at 1000 rpm for 30 min to obtain the fiberized material. (2) The fibrous material obtained in step (1) is rolled into a film by a roller press. The roller press temperature is 85℃ and the pressure is 2t. The film is then calendered into a dry film. (3) The dry film obtained in step (2) is passed through a differential roller press. The speed of roller A is 4 rpm, the speed of roller B is 1 rpm, the differential speed ratio of the two rollers is 4, and the temperature is 120℃. (4) The membrane obtained in step (3) is coated together with the current collector through a roller press to obtain a negative electrode sheet. The hot roller pressing temperature is 120℃ and the pressure is 1t.

[0035] Example 12 The method for improving direct lithiation efficiency in this embodiment includes the following steps: (1) Silicon-oxygen 450 (SiO) 450 The pre-lithiation material is obtained by mixing the pre-lithiation reagent with inert lithium powder (SLMP). The pre-lithiation reagent accounts for 3 wt% of the negative electrode active material. Then, conductive carbon black (SP) accounting for 1 wt% of the pre-lithiation material and fiberizable binder (PVDF) accounting for 2 wt% of the pre-lithiation material are added. The mixture is stirred at 1000 rpm for 30 min to obtain the fiberized material. (2) The fibrous material obtained in step (1) is rolled into a film by a roller press. The roller press temperature is 85℃ and the pressure is 0.5t. The film is then calendered into a dry film. (3) The dry film obtained in step (2) is passed through a differential roller press. The speed of roller A is 4 rpm, the speed of roller B is 1 rpm, the differential speed ratio of the two rollers is 4, and the temperature is 120℃. (4) The membrane obtained in step (3) is coated together with the current collector through a roller press to obtain a negative electrode sheet. The hot roller pressing temperature is 120℃ and the pressure is 1t.

[0036] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in step (3), the speed ratio of the differential rollers is 1, the speed of roller 1 is 1 rpm, and the speed of roller 2 is 1 rpm.

[0037] Comparative Example 2 The difference between Comparative Example 2 and Comparative Example 1 is that the proportion of the pre-lithiation reagent in step (1) is 2%; Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the proportion of the pre-lithiation reagent in step (1) is 4%; Comparative Example 4 The difference between Comparative Example 3 and Example 1 is that the proportion of the pre-lithiation reagent in step (1) is 5%; Comparative Example 5 This comparative example provides a method for inducing physical and chemical reactions using a hydraulic press. The difference from Example 1 is in step (3), where the dry diaphragm is pressed with a hydraulic press at a pressure of 100 MPa for 30 seconds. The remaining steps are the same as in Example 1.

[0038] The negative electrode sheets prepared in Examples 1-8 and Comparative Examples 1-5 were tested, and the test steps are as follows: First charge-discharge test: Coin cell half-cells were assembled using the negative electrode sheets obtained in Examples 1 to 8 and Comparative Examples 1 to 5 with lithium sheets. The electrolyte was 1.5M LiPF6 with an EC:EMC ratio of 3:7. The resulting coin cells were then subjected to their first charge-discharge test at a test temperature of 30°C and a rate of 0.05C.

[0039] Table 1 shows the first charge specific capacity, first discharge specific capacity, and first coulombic efficiency obtained from the assembly of half-cells prepared in the examples and comparative examples.

[0040] Table 1 As shown in Table 1, the initial coulombic efficiency of the diaphragm in Example 1 after differential roller rolling is significantly higher than that of Comparative Example 1 after constant-speed roller rolling, and also higher than that of Comparative Example 5 after hydraulic press lithiation. This is because the pressure generated by the constant-speed roller and the hydraulic press is vertical pressure without lateral shear force, resulting in limited SLMP deformation and a limited contact area between the SLMP and the active material, leading to less Li-Si alloy formation and thus a lower initial coulombic efficiency. Increasing the proportion of lithiation reagent (Comparative Examples 2-4) when using constant-speed roller rolling will increase the initial coulombic efficiency, but increasing the proportion of lithiation reagent will increase costs, and the improvement will be less than that of differential pre-lithiation.

[0041] As shown in Table 1, when using differential-induced lithiation, the differential ratio has a significant impact on the initial coulombic efficiency. When the differential ratio is too low (Example 5), the generated shear pressure is insufficient, resulting in less pressure-induced lithiation alloy phase (Li-Si) formation at the contact point between the pre-lithiation reagent and the active material, thus reducing the initial coulombic efficiency. When the differential ratio is too high (Example 2), the generated shear pressure is excessive. On the one hand, this causes significant deformation and structural damage to the SLMP, preventing effective lithiation. On the other hand, a large differential ratio can lead to diaphragm deformation and rupture, resulting in a decrease in the initial coulombic efficiency.

[0042] Figure 1 This is a schematic diagram of using a differential roller to press a film to induce lithiation. In the diagram, 1 and 2 are the two rollers A and B of the differential roller, which can rotate at different speeds. 3 is the film that needs to be lithilated.

[0043] Figure 2 The image shows the mixture after mixing in Example 1. As can be seen from the image, after mixing, PTFE undergoes fibrosis under shear force and coats the surface of the active material.

[0044] Figure 3 These are photos of the diaphragm before and after differential roller pressing in Example 1. It can be seen that a brighter area forms on the diaphragm surface after differential roller pressing. This is due to the presence of Li in the diaphragm. + Under pressure, the charge is transferred to silicon through a charge balance, forming a Li-Si alloy, thus achieving more efficient pre-lithiation.

[0045] Figure 4 The initial coulombic efficiency curve obtained from the charge-discharge process in Example 1 shows that the reversible capacity and initial coulombic efficiency after differential roller pressing are significantly increased compared to flat roller pressing (Comparative Example 1) and hydraulic pressure of hydraulic press (Comparative Example 5).

[0046] In summary, the differential roller-induced lithiation method in this invention can achieve better lithiation results with less lithium source, which not only improves lithiation efficiency and reduces costs, but also enables continuous and efficient lithiation of the electrode, thereby improving production efficiency.

[0047] This invention provides a simple method for pressure-induced pre-lithiation of silicon anodes. Under pressure, electrons in lithium metal near the contact point between the pre-lithiation reagent and the negative electrode active material migrate to silicon under the influence of the electric field formed by the potential difference between lithium and silicon, achieving physicochemical transformation. This invention mixes the negative electrode active material, pre-lithiation reagent, binder, and conductive agent to form a fibrous material, rolls it into a film, and then rolls it using differential speed rollers, utilizing the shear pressure generated between the two rollers to induce pre-lithiation. On one hand, the pre-lithiation reagent is added during the high-speed mixing process, ensuring uniform distribution of the pre-lithiation reagent on the surface of the active material while the binder is fibrous, thus improving the uniformity of pre-lithiation. On the other hand, the different shear forces generated by the different roller speed ratios of the differential speed rollers apply different pressures to the contact points between the lithiation reagent and the silicon material, inducing the formation of a lithium-silicon alloy, achieving efficient pre-lithiation.

[0048] The above embodiments based on the present invention are for illustrative purposes. Based on the above description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for improving direct lithiation efficiency, characterized in that... Includes the following steps: (1) Mixing: The negative electrode active material and the pre-lithiation reagent are pre-mixed using a degassing machine to obtain the pre-lithiation material. A conductive agent and a fiberizable binder are added to the pre-lithiation material and mixed at high speed to obtain the fiberized material. (2) Film formation: The fibrous material obtained in step (1) is rolled into a film by a roller press; (3) Induced lithiation: The film obtained in step (2) is rolled by a differential roller press at different differential speed ratios; (4) Coating: The membrane obtained in step (3) is laminated onto the copper current collector by hot rolling to obtain the negative electrode.

2. The method for improving direct lithiation efficiency according to claim 1, characterized in that, The negative electrode active material in step (1) includes any one or more of the following: nano-silicon materials, porous silicon, silicon-based composite materials, silicon oxides, silicon alloys, core-shell structured silicon, and three-dimensional structured silicon.

3. The method for improving direct lithiation efficiency according to claim 1, characterized in that, The pre-lithiation reagent is any one or more of the following: lithium metal reagent, lithium compound, organic lithium reagent, composite pre-lithiation reagent, and in-situ lithium source additive.

4. The method for improving direct lithiation efficiency according to claim 1, characterized in that, The conductive agent includes any one or more of single-walled carbon nanotubes, multi-arm carbon nanotubes, conductive carbon black, carbon fibers, or graphene.

5. The method for improving direct lithiation efficiency according to claim 1, characterized in that, The fiberizable adhesive includes one or more of thermoplastic polymer adhesives, conductive polymer adhesives, composite fiberizable adhesives, elastic adhesives, and low-melting-point adhesives.

6. The method for improving direct lithiation efficiency according to claim 1, characterized in that, In step (1), the pre-lithiation reagent accounts for 0.5wt%-6wt% of the negative electrode active material.

7. The method for improving direct lithiation efficiency according to claim 1, characterized in that, In step (1), the pre-lithiated material, conductive agent and fiberizable binder are mixed in different proportions, wherein the conductive agent and fiberizable binder account for 0.5wt%-2wt% of the pre-lithiated material, the high-speed mixing speed is 600-1600rpm, and the high-speed mixing time is 10-60min.

8. The preparation method for improving direct lithiation efficiency according to claim 1, characterized in that, In step (2), the temperature of the roller press is controlled at 60-150℃ and the pressure is 0.5-5t.

9. The preparation method for improving direct lithiation efficiency according to claim 1, characterized in that, The roller temperature of the differential roller press in step (3) is 110-150℃, and the differential speed ratio of the two rollers is 0.5-5 and the differential speed ratio is not 1.

10. The preparation method for improving direct lithiation efficiency according to claim 1, characterized in that, The hot roller pressing temperature in step (4) is 110-150℃ and the pressure is 0.5-5t.

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