A binder for silicon-carbon negative electrode of lithium-ion battery and preparation method thereof

Abstract

The invention discloses an adhesive for silicon-carbon negative electrode of lithium ion battery and a preparation method thereof, belonging to the technical field of lithium ion battery. The adhesive of the invention is obtained by imidization reaction of a polyamic acid solution formed by polycondensation reaction of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride and asymmetric structure aromatic diamine in a polar aprotic solvent in a molar ratio of 1:1; wherein the asymmetric structure aromatic diamine is 3,4'-diaminodiphenyl ether or 3,4'-diaminodiphenyl sulfide, or a combination of the two; the amount of the polar aprotic solvent is such that the solid content in the obtained polyamic acid solution is ≤5wt%. The battery further prepared by preparing the negative electrode slurry of lithium battery with the adhesive of the invention has excellent first coulomb efficiency and cycle stability.

Description

Technical Field

[0001] The invention relates to a lithium ion battery, and in particular to an adhesive for a silicon-carbon negative electrode of a lithium ion battery and a preparation method thereof. Background Art

[0002] Since lithium-ion batteries were developed by Sony in the 1990s, they have attracted widespread attention from academia and industry due to their high energy density, long cycle life, high voltage, no memory effect, fast charging and discharging, and green environmental protection. They are now widely used in 3C electronics, electric vehicles, and energy storage facilities. Especially in the field of new energy vehicles, high-density power batteries are the heart of the car, and the role of lithium batteries is self-evident.

[0003] Lithium-ion batteries mainly include four major components: positive electrode, negative electrode, electrolyte and separator. Among them, the positive electrode and negative electrode are usually composed of active materials, conductive agents, adhesives and collectors (current collectors). The adhesive accounts for a small proportion in the lithium-ion battery pole piece (usually 1.5-10wt%), and its main function is to effectively connect the various components together and form a complete pole piece structure.

[0004] Although carbon-based materials are commonly used in the negative electrode of lithium-ion batteries, in order to increase the energy density of the battery, research on negative electrode active materials containing silicon or tin alloys that can embed and deintercalate the theoretical capacity of lithium is becoming popular. However, the huge volume change rate of silicon-based materials can easily damage the active material layer (i.e., cause the negative electrode material to pulverize) and peel off from the collector, resulting in deterioration of the battery's cycle characteristics. Therefore, the development of a silicon-carbon negative electrode binder with excellent bonding properties, strong inhibition of volume expansion, and effective improvement of the reversible performance of lithium-ion battery cycles has become an urgent problem to be solved.

[0005] It is known that polyimide resins with high mechanical strength are used as binders in negative electrodes using silicon-based materials to solve this problem. For example, the invention patent with publication number CN112018391A proposes a cross-linked network silicon-carbon negative electrode binder and a silicon-carbon negative electrode sheet. The binder is obtained by thermal cross-linking of polyimide and polyvinyl alcohol, so it has the advantages of high tensile strength of polyimide and strong ability to inhibit the expansion of active substances. When it is used for silicon-carbon negative electrode sheets, it can improve the cycle reversibility of lithium-ion batteries (cycle stability is about 85% after 100 cycles at 25°C). Another example is the invention patent with publication number CN 114773599A, which discloses a block polyimide adhesive prepared from a block polyamic acid solution, wherein the block polyamic acid in the block polyamic acid solution is composed of rigid polyamic acid segments and flexible polyamic acid segments in the form of blocks; the molar ratio of the rigid polyamic acid segments to the flexible polyamic acid segments is (0.05-20):1; the solid content of the polyamic acid solution is 0.5-40wt%; and the intrinsic viscosity of the polyamic acid solution is 0.5-6.0dL / g. The polyimide adhesive prepared from the block polyamic acid provided by the invention has a stronger bonding force, and the lithium ion battery assembled with the lithium ion battery pole piece containing the block polyimide adhesive has a higher discharge specific capacity, capacity retention rate and better high temperature safety performance. Specifically, when it is applied to the positive electrode, the capacity retention rate of the lithium ion battery is about 80% after 100 cycles at 25°C. However, the improvement of the cycle stability by the above-mentioned polyimide resin adhesive is not ideal, and the first coulombic efficiency of the battery after being applied to lithium-ion secondary batteries has not been recorded. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a binder for silicon-carbon negative electrode of lithium ion battery and a preparation method thereof, which can make the obtained battery have excellent first coulomb efficiency and cycle stability.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A binder for a lithium-ion battery silicon-carbon negative electrode is obtained by an imidization reaction of a polyamic acid solution formed by a condensation polymerization reaction of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride (α-ODPA) and an asymmetric aromatic diamine in a polar aprotic solvent in a molar ratio of 1:1; wherein:

[0009] The asymmetric aromatic diamine is 3,4'-diaminodiphenyl ether (3,4'-ODA) or 3,4'-diaminodiphenyl sulfide (3,4'-ASD), or a combination of the two;

[0010] The polar aprotic solvent is used in an amount such that the solid content in the obtained polyamic acid solution is ≤5 wt %.

[0011] In the above binder for lithium ion battery silicon carbon negative electrode, the asymmetric aromatic diamine is preferably 3,4'-diaminodiphenyl ether, and the amount of the polar aprotic solvent is preferably such that the solid content in the obtained polyamic acid solution is 1-3 wt%.

[0012] The preparation method of the binder for silicon-carbon negative electrode of lithium ion battery of the present invention is as follows: 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride and asymmetric aromatic diamine are placed in a polar aprotic solvent at a molar ratio of 1:1 for polycondensation synthesis reaction, and the polyamic acid solution obtained by the reaction undergoes an imidization reaction to obtain the binder for silicon-carbon negative electrode of lithium ion battery; wherein,

[0013] The asymmetric aromatic diamine is 3,4'-diaminodiphenyl ether or 3,4'-diaminodiphenyl sulfide, or a combination of the two;

[0014] The polar aprotic solvent is used in an amount such that the solid content in the obtained polyamic acid solution is ≤5 wt %.

[0015] In the above preparation method, the asymmetric aromatic diamine is preferably 3,4'-diaminodiphenyl ether, the amount of polar aprotic solvent is preferably such that the solid content of the obtained polyamic acid solution is 1-3 wt %. The polycondensation reaction time is preferably greater than or equal to 72 h, more preferably 84-120 h.

[0016] When the adhesive described in the present invention is applied to the silicon-carbon negative electrode of a lithium-ion battery, it can effectively improve the cycle stability and the first coulomb efficiency (first efficiency) of the lithium-ion battery. The applicant's test results show that the battery prepared by further preparing the lithium battery negative electrode slurry using the adhesive described in the present invention has a first coulomb efficiency of ≥92%, a 120-cycle cycle stability efficiency of ≥98%, and a Z-direction (thickness direction) expansion rate of the electrode before and after 120 cycles of ≤68%. DETAILED DESCRIPTION

[0017] The adhesive for lithium-ion battery silicon-carbon negative electrode of the present invention is obtained by polycondensation reaction of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride and asymmetric aromatic diamine in a polar aprotic solvent at a molar ratio of 1:1, and the polyamic acid solution obtained by the reaction undergoes imidization reaction; wherein,

[0018] The asymmetric aromatic diamine is 3,4'-diaminodiphenyl ether or 3,4'-diaminodiphenyl sulfide, or a combination of the two;

[0019] The polar aprotic solvent is used in an amount such that the solid content in the obtained polyamic acid solution is ≤5 wt %.

[0020] In the present invention, the polyamic acid solution is also called polyamic acid resin, polyamic acid resin solution or polyimide precursor.

[0021] In the present invention, when the 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride and the asymmetric aromatic diamine are subjected to condensation synthesis reaction, the selection of the polar aprotic solvent used, and the temperature of the polycondensation reaction are the same as those in the prior art, such as polar aprotic solvents, preferably N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone. The amount of the polar aprotic solvent is preferably such that the solid content in the obtained polyamic acid solution is 1 to 3wt%. The time for the polycondensation reaction is preferably greater than or equal to 72h, and more preferably 84 to 120h.

[0022] The silicon-carbon negative electrode involved in the present invention refers to a negative electrode active material that is a silicon-carbon composite powder containing silicon or a silicon alloy, especially a silicon-carbon composite powder containing porous nano-silicon and its alloy.

[0023] The amount of the binder added in the present invention is the same as that in the prior art, and is usually controlled so that the amount of the solid components in the binder accounts for 1 to 6 wt % of the total solid components in the negative electrode slurry.

[0024] The battery prepared by using the binder of the present invention to prepare the negative electrode slurry of the lithium battery can have excellent first coulomb efficiency and cycle stability. The applicant believes through research and analysis that this may be due to the following reasons:

[0025] Firstly, under the premise of preparing the polyamic acid solution by polycondensation under low solid content conditions (weakening the interaction between the main chains of the polyamic acid molecular chain, increasing the probability of change in the geometric conformation of the polyamic acid molecular chain, reducing the possibility of the polyamic acid molecular chain forming an ordered structure, etc.), the molar ratio of the dianhydride raw material to the diamine raw material is controlled to be 1:1 and the polycondensation reaction time is extended to be greater than or equal to 72h. The polycondensation reaction has a tendency to form a ring, that is, a polyamic acid molecular chain with a quasi-cyclic (or semi-cyclic) structure can be formed, and α-ODPA (containing a twisted structure and non-coplanar benzene rings) is conducive to the formation of The obvious trend of forming a ring polymer; at the same time, there are no other atoms around the oxygen atom in the ether bond, and the internal rotation is easy) as a dianhydride polymerization monomer can effectively promote the polyamic acid molecular chain generated by the polycondensation reaction to form a unique spatial structure (conformation) and chain flexibility, that is, the molecular chain configuration is easy to change, which is conducive to reducing the complexity and diversity of the molecular structure shape. At the same time, with the asymmetric structure 3,4'-ODA and 3,4'-ASD as diamine polymerization monomers, the comprehensive effect can further affect the conformational change (chemical bond rotation) of the polyamic acid molecular chain to form a quasi-cyclic or semi-cyclic polyamic acid molecular chain. The formed quasi-cyclic or semi-cyclic polyamic acid molecular chain exists on the micro-nano silicon powder active material body in a "trap" and / or "tight hoop" manner (that is, it surrounds the surface of the micro-nano size active material or shuttles between its own nano-size pores), and the chemical bonds such as covalent bonds and hydrogen bonds contained in itself cooperate with the active groups on the surface of the silicon powder to form a strong adhesive force.

[0026] Secondly, the present application uses 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride as the polymerization monomer dianhydride raw material, and uses specific 3,4'-ODA and / or 3,4'-ASD as the polymerization monomer diamine raw material. The dianhydride raw material and the diamine raw material are both asymmetric structures. The asymmetric polyimide resin adhesive has a relatively obvious hole structure effect, and it is easy to form a loose molecular chain stacking, which is beneficial to lithium ion transmission; at the same time, a high degree of amorphous phase exists in the polyimide structure synthesized by condensation of asymmetric monomers, which can further optimize the lithium ion conduction in the lithium battery system. It can quickly migrate through the amorphous phase of the locally relaxed chain segment of the polyimide, further promoting the polyimide resin mixture to have good mechanical properties, high room temperature conductivity and a wide chemical stability window, etc., effectively improving the cycle stability, first coulomb efficiency and high rate characteristics of lithium ion batteries.

[0027] In order to better explain the technical solution of the present invention, the present invention is further described in detail below in conjunction with embodiments, but the embodiments of the present invention are not limited thereto.

[0028] Example 1

[0029] 1. Preparation of Adhesive

[0030] Take 11.769g (0.059mol) of 3,4'-ODA and stir and dissolve it in 970g of NMP, then add a total of 18.232g (0.059mol, added in 15 times) of α-ODPA (the molar ratio of dianhydride to diamine is 1:1), stir and react for 84h under nitrogen atmosphere and room temperature to obtain a polyamic acid solution with a solid content of 3% (the total solid content is about 30g), and the solution is a binder for silicon-carbon negative electrode of lithium-ion battery after imidization reaction.

[0031] 2. Preparation of positive and negative electrodes of lithium batteries

[0032] 2.1 Negative electrode:

[0033] The binder prepared in the above embodiment is directly used for the preparation of negative electrode slurry (no need to introduce solvent). Take 200g (in terms of solid content, the proportion in the negative electrode slurry is 3wt%), 188g of negative electrode active material (graphite 112.8g, nanoporous silicon powder 75.2g, graphite: nanoporous silicon powder = 6:4) and 6g of conductive carbon black (active material: binder: conductive agent = 94:3:3, weight ratio) and stir and mix evenly, and grind the resulting mixture 3 times with a three-roll grinder, and stir and mix with a stirring and degassing device for 2h to obtain a silicon-carbon composite negative electrode slurry (viscosity is about 5250cp). The silicon-carbon composite negative electrode slurry is evenly coated on the copper foil, and the gap between the coating roller (scraper) is adjusted to control the thickness of the negative electrode slurry after curing to be 35μm±3.0μm. The copper foil evenly coated with the negative electrode slurry was placed in an oven and heated at 80°C for 1 hour under the condition of flowing nitrogen and oxygen concentration below 20 ppm. The temperature was then increased to 320°C at a rate of 3.5°C / min and kept at 300°C for 2 hours to obtain the negative electrode sheet.

[0034] 2.2 Positive electrode:

[0035] The active material ternary positive electrode (NCM622): polyvinylidene fluoride: conductive carbon black was stirred and mixed evenly in a weight ratio of 94:3:3, and the solvent NMP was added to adjust the system to an appropriate viscosity (7000±500cp), and the mixture was placed in a three-roll mill for 3 hours and dispersed at high speed for 2 hours to obtain a positive electrode slurry. The positive electrode slurry was coated on aluminum foil using a doctor blade, and the gap between the coating roller (scraper) was adjusted to control the thickness of the positive electrode slurry after curing to be 100μm±5.0μm. The coated aluminum foil was placed in an oven and kept at 120°C for 2 hours under air circulation to obtain a positive electrode sheet.

[0036] 3. Preparation of Cells

[0037] In order to reduce the gaps between the active materials, the negative electrode sheets and positive electrode sheets of the lithium battery were appropriately rolled using a roller press. The rolled negative electrode sheets and positive electrode sheets were cut into discs with a diameter of 14 mm using a punching machine. 2 O<0.01ppm O 2 <0.01ppm) assemble CR2032 button battery, assemble the negative electrode shell, negative electrode sheet, diaphragm, positive electrode sheet, nickel foam, spring sheet, positive electrode shell in sequence, and drip 1ml of electrolyte at both ends of the diaphragm respectively. The electrolyte is 1.0mol / L LiPF 6 The assembled battery was dissolved in a mixed solution of EC and DMC (EC:DMC=1:1, volume ratio), and the packaging pressure was 75MPa in a sealing machine. After standing for 24h, the corresponding electrochemical performance test was carried out.

[0038] 4. Charge and discharge characteristics test

[0039] Each group of batteries manufactured by the above method was subjected to a cyclic charge and discharge characteristic test. The batteries were subjected to charge and discharge tests and cycle tests at 25°C. The experiment adopted a 0.2C current charge and discharge test with a voltage window of 0.005 to 1.5V. The amount of electricity flowing from the start of charging or discharging to the end was defined as the charge capacity or discharge capacity.

[0040] The charge and discharge efficiency of the battery was tested for the first time and after 120 cycles [charge and discharge efficiency = (discharge capacity / charge capacity)*100%).

[0041] The thickness of the negative electrode sheet in the scanning electron microscope cross-section of the battery before and after 120 cycles of charging and discharging with the adhesive was used as a reference, and the expansion rate of the negative electrode sheet was calculated based on the thickness of the active material of the electrode sheet before charging and the thickness of the active material of the electrode sheet after 120 cycles. 0 , measure the thickness H of the negative electrode after 120 cycles 120 , and according to the calculation formula (thickness direction Z) expansion rate = (H 120 -H 0 ) / H 0 *100% calculated pole piece expansion rate.

[0042] The test results are: the first coulomb efficiency is 94%, the capacity retention rate after 120 cycles is 98%, and the electrode expansion rate is 62%.

[0043] Comparative Example 1-1

[0044] Take 11.300g (0.056mol) of 3,4'-ODA and stir and dissolve it in 970g of NMP, then add a total of 18.232g (0.059mol, added in 15 times) of α-ODPA (the molar ratio of dianhydride to diamine is 1:0.96), stir and react for 82h under nitrogen atmosphere and room temperature to obtain a polyamic acid solution with a solid content of 3% (the total solid content is about 30g), and the solution is a binder for silicon-carbon negative electrode of lithium-ion battery after imidization reaction.

[0045] The preparation of the positive and negative electrodes of the lithium-ion battery, the preparation of the battery and the charge and discharge characteristics test are the same as in Example 1.

[0046] The test results are: the initial coulombic efficiency is about 88%, the capacity retention rate after 120 cycles is about 90%, and the expansion rate of the electrode in the Z direction (thickness direction) after 120 cycles is about 86%.

[0047] Comparative Example 1-2

[0048] Take 11.769g (0.059mol) of 3,4'-ODA and stir and dissolve it in 970g of NMP, then add a total of 17.503g (0.056mol, added in 15 times) of α-ODPA (the molar ratio of dianhydride to diamine is 0.96:1), stir and react for 82h under nitrogen atmosphere and room temperature to obtain a polyamic acid solution with a solid content of 3% (the total solid content is about 30g), and the solution is a binder for silicon-carbon negative electrode of lithium-ion battery after imidization reaction.

[0049] The preparation of the positive and negative electrodes of the lithium-ion battery, the preparation of the battery and the charge and discharge characteristics test are the same as in Example 1.

[0050] The test results are: the initial coulomb efficiency is about 90%, the capacity retention rate after 120 cycles is about 91%, and the expansion rate of the electrode in the Z direction (thickness direction) after 120 cycles is about 85%.

[0051] Comparative Examples 1-3

[0052] Example 1 was repeated except that α-ODPA was replaced with an equimolar amount of 2,3,3',4'-biphenyltetracarboxylic dianhydride (α-BPDA).

[0053] The test results are: the initial coulombic efficiency is about 90%, the capacity retention rate after 120 cycles is about 93%, and the expansion rate of the electrode in the Z direction (thickness direction) after 120 cycles is about 89%.

[0054] Comparative Examples 1-4

[0055] Example 1 was repeated except that 3,4'-ODA was replaced with an equimolar amount of 4,4'-diaminodiphenyl ether (4,4'-ODA).

[0056] The test results are: the initial coulombic efficiency is about 86%, the capacity retention rate after 120 cycles is about 89%, and the expansion rate of the electrode in the Z direction (thickness direction) after 120 cycles is about 96%.

[0057] Comparative Examples 1-5

[0058] 1. Preparation of Adhesive

[0059] Take 23.567g (0.118mol) of 3,4'-ODA and stir and dissolve it in 970g of NMP, then add a total of 36.464g (0.118mol, added in 15 times) of α-ODPA (the molar ratio of dianhydride to diamine is 1:1), stir and react for 84h under nitrogen atmosphere and room temperature to obtain a polyamic acid solution with a solid content of 6% (the total solid content is about 60g), and the solution is a binder for silicon-carbon negative electrode of lithium-ion battery after imidization reaction.

[0060] The preparation of the positive and negative electrodes of the lithium-ion battery, the preparation of the battery and the charge and discharge characteristics test are the same as in Example 1.

[0061] The test results are: the initial coulombic efficiency is about 90%, the capacity retention rate after 120 cycles is about 94%, and the expansion rate of the electrode in the Z direction (thickness direction) after 120 cycles is about 73%.

[0062] Example 2

[0063] 1. Preparation of Adhesive

[0064] Take 2.354g (0.0118mol) of 3,4'-ODA and stir and dissolve it in 594g of NMP, then add a total of 3.647g (0.0118mol, added in 12 times) of α-ODPA (the molar ratio of dianhydride to diamine is 1:1), stir and react for 72h under nitrogen atmosphere and room temperature to obtain a polyamic acid solution with a solid content of 1% (the total solid content is about 6g), and the solution is a binder for silicon-carbon negative electrode of lithium-ion battery after imidization reaction.

[0065] The preparation of the positive and negative electrodes of the lithium-ion battery, the preparation of the battery and the charge and discharge characteristics test are the same as in Example 1.

[0066] The test results are: the initial coulomb efficiency is about 94%, the capacity retention rate after 120 cycles is about 99%, and the expansion rate of the electrode in the Z direction (thickness direction) after 120 cycles is about 58%.

[0067] Example 3

[0068] Example 1 was repeated, except that 3,4'-ASD was used in an equal molar amount to replace 3,4'-ODA, and NMP was added in an amount such that the solid content of the obtained polyamic acid solution was controlled to be 5%.

[0069] The test results are: the initial coulombic efficiency is about 92%, the capacity retention rate after 120 cycles is about 98%, and the expansion rate of the electrode in the Z direction (thickness direction) after 120 cycles is about 68%.

[0070] Comparative Example 3-1

[0071] Example 3 was repeated, except that the amount of NMP added was such that the solid content of the obtained polyamic acid solution was controlled to be 6%.

[0072] The test results are: the first coulomb efficiency is about 89.5%, the capacity retention rate after 120 cycles is about 92%, and the expansion rate of the electrode in the Z direction (thickness direction) after 120 cycles is about 76%.

[0073] Example 4

[0074] 1. Preparation of Adhesive

[0075] Take 5.811g (0.029mol) of 3,4'-ODA and 4.185g (0.020mol) of 3,4'-ASD (the molar ratio of 3,4'-ODA to 3,4'-ASD is 6:4) and stir to dissolve in 475g of NMP, then add a total of 15.005g (0.049mol, added in 8 times) of α-ODPA (the molar ratio of dianhydride to diamine is 1:1), stir and react for 120h under nitrogen atmosphere and room temperature to obtain a polyamic acid solution with a solid content of 5% (the total solid content is about 25g), and the solution is a binder for silicon-carbon negative electrode of lithium ion battery after imidization reaction.

[0076] The preparation of the positive and negative electrodes of the lithium-ion battery, the preparation of the battery and the charge and discharge characteristics test are the same as in Example 1.

[0077] The test results are: the initial coulombic efficiency is about 92%, the capacity retention rate after 120 cycles is about 98%, and the expansion rate of the electrode in the Z direction (thickness direction) after 120 cycles is about 68%.

Claims

1. A binder for a lithium-ion battery silicon-carbon negative electrode, characterized in that: It is obtained by imidization reaction of a polyamic acid solution formed by polycondensation reaction of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride and asymmetric aromatic diamine in a polar aprotic solvent at a molar ratio of 1:1; wherein, The asymmetric aromatic diamine is 3,4'-diaminodiphenyl ether or 3,4'-diaminodiphenyl sulfide, or a combination of the two; The polar aprotic solvent is used in an amount such that the solid content in the obtained polyamic acid solution is ≤5wt%; The time of the polycondensation reaction is greater than or equal to 72 hours.

2. The binder for silicon-carbon negative electrode of lithium-ion battery according to claim 1, characterized in that: The polar aprotic solvent is used in an amount such that the solid content in the obtained polyamic acid solution is 1-3 wt %.

3. The method for preparing the binder for silicon-carbon negative electrode of lithium ion battery according to claim 1, characterized in that: 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride and asymmetric aromatic diamine are placed in a polar aprotic solvent at a molar ratio of 1:1 for polycondensation synthesis reaction, and the polyamic acid solution obtained by the reaction undergoes an imidization reaction to obtain the binder for silicon-carbon negative electrode of lithium ion battery; wherein, The asymmetric aromatic diamine is 3,4'-diaminodiphenyl ether (3,4'-ODA) or 3,4'-diaminodiphenyl sulfide, or a combination of the two; The polar aprotic solvent is used in an amount such that the solid content in the obtained polyamic acid solution is ≤5 wt %.

4. The preparation method according to claim 3, characterized in that: The amount of the polar aprotic solvent used is such that the solid content in the obtained polyamic acid solution is 1 to 3 wt %.

5. The preparation method according to claim 3, characterized in that: The time of the condensation synthesis reaction is 84~120h.