Negative electrode sheet and preparation method thereof, and secondary battery having the same

Abstract

The present application provides a negative electrode sheet and a preparation method thereof, a secondary battery having the same, a battery module, a battery pack and an electric device. The negative electrode sheet of the present application comprises a reduced graphene oxide sheet and a modified nano negative electrode material, wherein the modified nano negative electrode material comprises: a core; and a coating layer coated on the surface of the core, wherein the molecular formula of the core is A x B y , wherein A is at least one selected from antimony, molybdenum, and silicon, B is at least one selected from sulfur, selenium, and oxygen, 1≤x≤3, 1≤y≤4, and the coating layer includes polydopamine. The negative electrode sheet of the present application has a high tensile modulus and tensile strength, which can improve the energy density of the secondary battery and extend the cycle life.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular to a negative electrode plate and a preparation method thereof, a secondary battery having the same, and a battery module, a battery pack and an electrical device. Background Art

[0002] Secondary batteries are widely used due to their reliable performance, no pollution, and no memory effect. For example, as environmental protection issues are increasingly valued and new energy vehicles become more popular, the demand for power secondary batteries will show explosive growth. However, as the application scope of secondary batteries becomes wider and wider, the performance of secondary batteries is also severely challenged.

[0003] Researching and developing negative electrode materials with excellent performance is the key to improving the performance of secondary batteries. Most negative electrode materials face problems such as large volume expansion and poor conductivity. How to improve the conductivity of negative electrode materials while reducing or avoiding the reduction in electrochemical performance due to their volume expansion is the current technical difficulty. Summary of the invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode plate and its preparation method, a secondary battery having the same, as well as a battery module, a battery pack and an electrical device. The negative electrode plate has a high tensile modulus and tensile strength, which can improve the capacity and cycle characteristics of the secondary battery.

[0005] In order to achieve the above-mentioned object, the first aspect of the present application is to provide a negative electrode sheet, wherein the negative electrode sheet is stacked by a reduced graphene oxide sheet layer and a modified nano negative electrode material, wherein the modified nano negative electrode material comprises: a core; and a coating layer coated on the surface of the core, wherein the molecular formula of the core is A x B y , wherein A is at least one selected from antimony, molybdenum, and silicon, B is at least one selected from sulfur, selenium, and oxygen, 1≤x≤3, 1≤y≤4, and the coating layer includes polydopamine.

[0006] By coating polydopamine on the core of the nano-negative electrode material and using the polydopamine-modified nano-negative electrode material, the interaction between the negative electrode material and reduced graphene oxide can be enhanced. The resulting negative electrode sheet has a higher tensile modulus and tensile strength, which can improve the energy density of the secondary battery and extend the cycle life.

[0007] In some embodiments, the mass ratio of the core to the coating layer is 2: 1 to 1: 3. By making the mass ratio of the core to the coating layer within this range, the tensile modulus and tensile strength of the pole piece are further improved, and the energy density of the secondary battery can be increased, and the cycle life can be extended.

[0008] In some embodiments, the coating layer has a coverage of 80% or more. When the coating layer has a coverage within the above range, the tensile modulus and tensile strength of the pole piece are further improved, and the energy density of the secondary battery can be increased, thereby extending the cycle life.

[0009] In some embodiments, the coating layer has a thickness of 15 nm to 42 nm. When the coating layer has a thickness within this range, the tensile modulus and tensile strength of the pole piece can be further improved, and the energy density of the secondary battery can be increased, thereby extending the cycle life.

[0010] In some embodiments, the mass ratio of the modified nanometer negative electrode material to the reduced graphene oxide is 1: 2 to 1: 1. By further setting the mass ratio of the modified nanometer negative electrode material to the reduced graphene oxide within this range, the cycle performance improvement effect of the battery can be effectively exerted.

[0011] In some embodiments, the tensile modulus of the negative electrode plate is 175 GPa to 700 GPa. By setting the tensile modulus of the negative electrode plate within this range, both the energy density and the cycle characteristics of the secondary battery can be taken into account.

[0012] In some embodiments, the tensile strength of the negative electrode sheet is 3.4 MPa to 9.3 MPa. By setting the tensile strength of the negative electrode sheet within this range, both the energy density and the cycle characteristics of the secondary battery can be taken into account.

[0013] The second aspect of the present application is to provide a method for preparing a negative electrode sheet according to the first aspect of the present application, comprising the following steps (1) to (3):

[0014] Step (1): homogenizing the core material and dopamine in a tris buffer;

[0015] Step (2): dispersing the product of step (1) in a graphene oxide solution, reducing it at a first temperature and then performing vacuum filtration, pre-freezing the obtained filter membrane at a second temperature, and freeze-drying the pre-frozen material at a third temperature to obtain a porous film;

[0016] Step (3): calcining the film obtained in step (2) under an inert and / or reducing atmosphere to obtain the negative electrode sheet. The negative electrode sheet thus obtained has a high tensile modulus and tensile strength, which can improve the energy density of the secondary battery and extend the cycle life.

[0017] In some embodiments, in the step (1), the homogenization treatment is carried out by ultrasonication and stirring for 6 to 24 hours. Thus, good coating of polydopamine can be achieved, and the tensile modulus and tensile strength of the electrode can be improved.

[0018] In some embodiments, in the step (2), the first temperature is 80° C. to 100° C., and the reduction time is 2 min to 30 min. Thus, the graphene oxide can be well reduced, the film forming property is improved, and the tensile modulus and tensile strength of the pole piece are increased.

[0019] In some embodiments, in the step (2), the second temperature is -200°C to -80°C, the third temperature is -30°C to -50°C, and the freeze-drying time is 16 hours to 48 hours. Thus, the film forming property can be improved, and the tensile modulus and tensile strength of the electrode piece can be increased.

[0020] In some embodiments, in the step (3), the calcination is performed at 100° C. to 550° C. for 0.5 h to 5 h. Thus, an electrode sheet with good electrochemical characteristics can be obtained.

[0021] The third aspect of the present application is to provide a secondary battery, which includes the negative electrode sheet according to the first aspect of the present application or the negative electrode sheet prepared according to the preparation method described in the second aspect of the present application.

[0022] A fourth aspect of the present application is to provide a battery module, which includes the secondary battery according to the third aspect of the present application.

[0023] A fifth aspect of the present application is to provide a battery pack, which includes the battery module according to the fourth aspect of the present application.

[0024] The sixth aspect of the present application is to provide an electrical device, which includes at least one of the secondary battery according to the third aspect of the present application, the battery module according to the fourth aspect of the present application, and the battery pack according to the fifth aspect of the present application.

[0025] According to the present application, the tensile modulus and tensile strength of the pole piece can be improved, and the energy density of the secondary battery can be increased, thereby extending the cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0027] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0028] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0029] Figure 4 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0030] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0031] Figure 6 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0032] Description of reference numerals:

[0033] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly DETAILED DESCRIPTION

[0034] Below, the embodiments of the positive electrode active material and its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack and electrical device of the present application are specifically disclosed with appropriate reference to the drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0035] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0036] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0037] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0038] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0039] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0040] [Negative electrode]

[0041] In one embodiment of the present application, the present application proposes a negative electrode sheet, which is stacked by a reduced graphene oxide sheet and a modified nano negative electrode material, wherein the modified nano negative electrode material comprises: a core; and a coating layer coated on the surface of the core, wherein the molecular formula of the core is A x B y , wherein A is at least one selected from antimony, molybdenum, and silicon, B is at least one selected from sulfur, selenium, and oxygen, 1≤x≤3, 1≤y≤4, and the coating layer includes polydopamine.

[0042] Specifically, the core may be at least one selected from nano-sulfide, nano-selenide, nano-oxide, and nano-selenium sulfide.

[0043] Although the mechanism is not clear, the applicant unexpectedly found that the introduction of polydopamine improves the dispersibility of the nano-negative electrode material in water, ensures its uniform dispersion in the reduced graphene oxide film, and promotes the reduction and self-assembly of the graphene oxide sheets, and can serve as a link to enhance the interaction between the nano-negative electrode material and the reduced graphene oxide sheets. The reduced graphene oxide sheets and the sheets can be cross-linked with polydopamine to improve the nano-negative electrode material. After carbonization, polydopamine can evolve into a nitrogen-doped carbon layer to improve the electrochemical performance of the nano-negative electrode material.

[0044] By coating polydopamine on the core of the nano-negative electrode material and using the polydopamine-modified nano-negative electrode material, the interaction between the negative electrode material and reduced graphene oxide can be enhanced. The resulting negative electrode sheet has a higher tensile modulus and tensile strength, which can improve energy density and extend cycle life.

[0045] The inventor of the present application speculates that polydopamine can form a uniform coating layer on the surface of the nano-negative electrode, which ensures that the nano-negative electrode material is uniformly dispersed in the graphene oxide aqueous solution, and at the same time achieves close bonding with the graphene oxide sheet layer, and well encapsulates the nano-negative electrode material between the graphene oxide sheets, effectively alleviating the volume expansion of the nano-negative electrode material and improving the conductivity. On the other hand, polydopamine can evolve into a nitrogen-doped carbon layer after calcination, effectively improving the electrochemical performance of the nano-negative electrode material. In addition, polydopamine can also act as a reducing agent for graphene oxide, avoiding the use of toxic / dangerous reducing agents such as hydrazine hydrate and hydroiodic acid, and the preparation process is relatively green and environmentally friendly.

[0046] In addition, the negative electrode plate of the present application is a porous self-supporting plate, which is conducive to the transmission of electrons and ions, enhances the electrochemical properties of the negative electrode material, avoids the use of binders and conductive agents, and can simplify the process flow.

[0047] In addition, the negative electrode plate of the present application can be widely used in the fields of lithium batteries, sodium batteries, solar cells, photocatalysis, etc.

[0048] In some embodiments, optionally, the mass ratio of the core to the coating is 2:1 to 1:3. By making the mass ratio of the core to the coating within this range, the tensile modulus and tensile strength of the pole piece can be further improved, and the energy density of the secondary battery can be improved, and the cycle life can be extended. By making the mass ratio of the core to the coating within a suitable range, on the one hand, a good coating effect can be achieved, the tensile modulus and tensile strength of the pole piece can be improved, so that the negative electrode material is not easy to fall off from the surface of the reduced graphene oxide after expansion, and the cycle performance of the secondary battery can be improved; on the other hand, the energy density can be avoided from being reduced and the capacity of the secondary battery can be improved.

[0049] In some embodiments, optionally, the coating layer has a coating rate of 80% or more. Here, the coating rate can be calculated from the cross-section of the modified nano-negative electrode particles as a percentage to show the extent to which the surface of the inner core is coated with polydopamine. For example, the average value of 50 modified nano-negative electrode particles can be taken. By having the coating rate of the coating layer within the above range, the tensile modulus and tensile strength of the pole piece can be further improved, and the energy density of the secondary battery can be improved, and the cycle life can be extended. By having the coating rate of the coating layer within the above range, the negative electrode material is not easy to fall off from the surface of the reduced graphene oxide after expansion, thereby improving the cycle performance of the secondary battery.

[0050] In some embodiments, optionally, the coating layer has a thickness of 15 nm to 42 nm. When the coating layer has a thickness within this range, the tensile modulus and tensile strength of the pole piece are further improved, and the energy density of the secondary battery can be improved, thereby extending the cycle life. When the coating layer has a thickness within the above range, on the one hand, a good coating effect can be achieved, the tensile modulus and tensile strength of the pole piece can be improved, and the negative electrode material is not easy to fall off from the surface of the reduced graphene oxide after expansion, thereby improving the cycle performance of the secondary battery; on the other hand, the energy density can be avoided from being too low, thereby improving the capacity of the secondary battery.

[0051] In some embodiments, optionally, the mass ratio of the modified nano-anode material to the reduced graphene oxide is 1:2 to 1:1. By further setting the mass ratio of the modified nano-anode material to the reduced graphene oxide within this range, the cycle performance improvement of the battery can be effectively exerted. By setting the mass ratio of the modified nano-anode material to the reduced graphene oxide within the above range, on the one hand, the film forming property can be improved, thereby forming a thin film electrode well; on the other hand, the energy density can be avoided from being too low, and the capacity of the secondary battery can be increased.

[0052] Furthermore, in another embodiment of the present application, the present application proposes a method for preparing a negative electrode sheet, comprising the following steps (1) to (3):

[0053] Step (1): homogenizing the core material and dopamine in a tris buffer;

[0054] Step (2): dispersing the product of step (1) in a graphene oxide solution, reducing it at a first temperature and then performing vacuum filtration, pre-freezing the obtained filter membrane at a second temperature, and freeze-drying the pre-frozen material at a third temperature to obtain a porous film;

[0055] Step (3): calcining the film obtained in step (2) under an inert and / or reducing atmosphere to obtain the negative electrode sheet. The negative electrode sheet thus obtained has a high tensile modulus and tensile strength, which can improve the energy density of the secondary battery and extend the cycle life.

[0056] In some embodiments, in the step (1), the homogenization treatment is carried out by ultrasonication and stirring for 6 to 24 hours. Thus, good coating of polydopamine can be achieved, and the tensile modulus and tensile strength of the electrode can be improved.

[0057] In some embodiments, in the step (2), the first temperature is 80° C. to 100° C., and the reduction time is 2 min to 30 min. Thus, the graphene oxide can be well reduced, the film forming property is improved, and the tensile modulus and tensile strength of the pole piece are increased.

[0058] In some embodiments, in the step (2), the second temperature is -200°C to -80°C, the third temperature is -30°C to -50°C, and the freeze-drying time is 16 hours to 48 hours. Thus, the film forming property can be improved, and the tensile modulus and tensile strength of the electrode piece can be increased.

[0059] In some embodiments, in the step (3), the calcination is performed at 100° C. to 550° C. for 0.5 h to 5 h. Thus, an electrode sheet with good electrochemical characteristics can be obtained.

[0060] By adjusting the specific conditions in the above process, the negative electrode sheet of the present application can be obtained.

[0061] In addition, the secondary battery, battery module, battery pack, and electric device of the present application will be described below with reference to the drawings as appropriate.

[0062] [Secondary battery]

[0063] In one embodiment of the present application, a secondary battery is provided.

[0064] Generally, a secondary battery includes a negative electrode sheet, a positive electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0065] [Positive electrode]

[0066] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0067] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0068] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0069] In some embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi1 / 3Co1 / 3Mn1 / 3O2 (also referred to as NCM333), LiNi0.5Co0.2Mn0.3O2 (also referred to as NCM523), LiNi0.5Co0.25Mn0.25O2 (also referred to as NCM211), LiNi0.6Co At least one of 0.2Mn0.2O2 (also referred to as NCM622), LiNi0.8Co0.1Mn0.1O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi0.85Co0.15Al0.05O2) and modified compounds thereof. Examples of lithium phosphates containing an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0070] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0071] In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0072] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0073] In addition, as the positive electrode plate, the positive electrode active material may also include one or more of sodium transition metal oxides, polyanionic compounds and Prussian blue compounds.

[0074] Examples of the sodium transition metal oxides include:

[0075] Na 1-x Cu h Fe k Mn l M 1 m O 2-y , where M 1 It is one or more of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn and Ba, 0 <x≤0.33,0<h≤0.24,0≤k≤0.32,0<l≤0.68,0≤m<0.1,h+k+l+m=1,0≤y<0.2;

[0076] Na 0.67 Mn 0.7 Ni z M 2 0.3-z O2, where M 2 is one or more of Li, Mg, Al, Ca, Ti, Fe, Cu, Zn and Ba, 0 <z≤0.1;

[0077] Na a Li b Ni c Mn d Fe e O2, of which 0.67 <a≤1,0<b<0.2,0<c<0.3,0.67<d+e<0.8,b+c+d+e=1。

[0078] Examples of the polyanionic compound include:

[0079] A 1 f M 3 g (PO4) i O j X 1 3-j , wherein A is one or more of H, Li, Na, K and NH4, M 3 is one or more of Ti, Cr, Mn, Fe, Co, Ni, V, Cu and Zn, X 1is one or more of F, Cl, and Br, 0 < f ≤ 4, 0 < g ≤ 2, 1 ≤ i ≤ 3, 0 ≤ j ≤ 2;

[0080] Na n M 4 PO4X 2 , where M 4 is one or more of Mn, Fe, Co, Ni, Cu, and Zn, X 2 is one or more of F, Cl, and Br, 0 < n ≤ 2;

[0081] Na p M 5 q (SO4)3, where M 5 is one or more of Mn, Fe, Co, Ni, Cu, and Zn, 0 < p ≤ 2, 0 < q ≤ 2;

[0082] Na s Mn t Fe 3-t (PO4)2(P2O7), where 0 < s ≤ 4, 0 ≤ t ≤ 3, for example, t is 0, 1, 1.5, 2, or 3.

[0083] As an example of the above Prussian blue compounds, for example, the following can be listed:

[0084] A u M 6 v [M 7 (CN)6] w ·xH2O, where A is H + 、NH4 + 、an alkali metal cation, and an alkaline earth metal cation, M 6 and M 7 are each independently one or more of transition metal cations, 0 < u ≤ 2, 0 < v ≤ 1, 0 < w ≤ 1, 0 < x < 6. For example, A is H + 、Li + 、Na + 、K + 、NH4 + 、Rb + 、Cs + 、Fr + 、Be 2+ 、Mg 2+ 、Ca 2+ 、Sr 2+ 、Ba 2+ and Ra 2+ among one or more, M 6 and M 7Each is independently a cation of one or more transition metal elements selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn and W. Preferably, A is Li + 、Na + and K + One or more of M 6 Mn is a cation of one or more transition metal elements among Mn, Fe, Co, Ni and Cu. 7 It is a cation of one or more transition metal elements among Mn, Fe, Co, Ni and Cu.

[0085] The positive electrode active material layer may also optionally include a conductive agent and a binder. The conductive agent is used to improve the conductivity of the positive electrode active material layer, and the binder is used to firmly bind the positive electrode active material and the binder to the positive electrode current collector. The present application does not specifically limit the types of the conductive agent and the binder, and they can be selected according to actual needs.

[0086] As an example, the conductive agent can be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers; the binder can be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA) and polyvinyl alcohol (PVA).

[0087] The positive electrode current collector can be made of metal foil, carbon-coated metal foil or porous metal plate, preferably aluminum foil.

[0088] [Isolation film]

[0089] As the above-mentioned isolation membrane, the present application has no special restrictions, and any known porous structure isolation membrane with electrochemical stability and mechanical stability can be selected according to actual needs. For example, it can be a single-layer or multi-layer film containing one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0090] [Electrolyte]

[0091] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0092] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt, a solvent, and an additive.

[0093] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0094] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0095] In some embodiments, the electrolyte includes additives, and the additives include fluoroethylene carbonate and / or vinylene carbonate. In addition, it may also include other additives, such as: negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery, etc.

[0096] The electrolyte may also include an organic solvent and a sodium salt, and any organic solvent and sodium salt that can be used in sodium ion batteries can be selected according to actual needs. As an example, the organic solvent may be one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC); the sodium salt may be one or more of NaPF6, NaClO4, NaBCl4, NaSO3CF3 and Na(CH3)C6H4SO3.

[0097] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0098] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0099] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0100] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 1 The secondary battery 5 is a square structure as an example.

[0101] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0102] Battery Module

[0103] In some embodiments, secondary batteries may be assembled into a battery module. The number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0104] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0105] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0106] Battery Pack

[0107] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0108] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0109] Electrical devices

[0110] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0111] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0112] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0113] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0114] Example

[0115] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0116] <Example 1>

[0117] ① Preparation of negative electrode

[0118] In Example 1, the method for preparing the negative electrode sheet includes the following steps (1) to (3), wherein the specific conditions of the steps (1) to (3) are shown in Table 1:

[0119] (1) Nano-antimony sulfide and dopamine in a mass ratio of 2:1 were placed in a tris buffer solution, ultrasonically treated and stirred at room temperature for 12 h, and then centrifuged and washed after mixing evenly;

[0120] (2) 20 mg of the product of step (1) was dispersed in 20 mL of graphene oxide solution (1 mg / mL), and after being dispersed uniformly by ultrasonic / stirring, it was reduced at -90°C for 30 min and then vacuum filtered. The obtained filter membrane was frozen at -200°C, and the pre-frozen material was freeze-dried at -40°C for 24 h to obtain a porous film;

[0121] (3) The thin film obtained in step (2) is calcined and reduced at 450° C. for 4 h in an inert / reducing atmosphere to obtain an electrode.

[0122] The parameters of the negative electrode are shown in Table 2.

[0123] ② Performance Evaluation

[0124] The negative electrode sheet prepared in the above step ① was tested for performance by the following method. The results are shown in Table 3.

[0125] (i) Tensile modulus test

[0126] The graphene film was subjected to static mechanical uniaxial in-plane tensile tests using a dynamic mechanical analyzer (2980DMA, TA Instruments) in tensile mode to collect the tensile strength and tensile modulus of the film. The test dimensions of the film samples were 25-30 mm in length and 3-7 mm in width. The graphene film was clamped by a test fixture, and all tensile tests were performed in controlled force mode.

[0127] (ii) Tensile strength test

[0128] The graphene film was subjected to static mechanical uniaxial in-plane tensile tests using a dynamic mechanical analyzer (2980DMA, TA Instruments) in tensile mode to collect the tensile strength and tensile modulus of the film. The test dimensions of the film samples were 25-30 mm in length and 3-7 mm in width. The graphene film was clamped by a test fixture, and all tensile tests were performed in controlled force mode.

[0129] (iii) Method for preparing button cell

[0130] For the negative electrode active material prepared in the above step ①, a metal sodium sheet was used as the counter electrode, a Whatham glass fiber separator was used, and 1M NaClO4 / EC-DEC (1:1, v / v) + 5% FEC electrolyte was injected to assemble a button cell.

[0131] (iv) Button cell battery cycle performance test

[0132] At 25°C and normal pressure, discharge the button cell at a constant current of 0.1C to a voltage of 0.005V, and then discharge at a constant current of 0.05C to a voltage of 0.005V, and record the discharge specific capacity at this time, which is the first lithium insertion capacity; then charge at a constant current of 0.1C to a voltage of 1.5V, and record the charge specific capacity at this time, which is the first lithium removal capacity. Perform 100 cycles of charge and discharge test on the button cell according to the above method, and record the lithium removal capacity each time.

[0133] Cycle capacity retention rate of negative electrode active material (%) = 100th lithium removal capacity / first lithium removal capacity × 100%

[0134] <Example 2> to <Example 9>, <Comparative Example 1> to <Comparative Example 4>

[0135] In Examples 2 to 9 and Comparative Examples 1 to 4, except for changing the specific conditions in steps (1) to (3) as shown in Table 1 and changing the type and content of each raw material as shown in Table 2, the same preparation method as in Example 1 was adopted to obtain a negative electrode sheet.

[0136] <Comparative Example 5>

[0137] The same preparation method as in Example 1 was adopted except that step (1) shown in Table 1 was not performed and raw material 2 shown in Table 2 was not used, thereby obtaining a negative electrode sheet.

[0138]

[0139] [Table 2]

[0140]

[0141] [Table 3]

[0142]

[0143] From the above Tables 1 to 3, we can see the following:

[0144] It can be seen from Examples 1 to 9 and Comparative Example 5 that, in the negative electrode plate of the present application, by introducing polydopamine-coated nano-negative electrode materials, the tensile modulus and tensile strength of the plate can be improved, and the energy density of the secondary battery can be improved, thereby extending the cycle life.

[0145] It can be seen from Examples 1 to 4 and Comparative Examples 1 and 2 that in the negative electrode sheet of the present application, the mass ratio of the core to the coating layer is within a specific range, which can further improve the tensile modulus and tensile strength of the electrode sheet, and can also increase the energy density of the secondary battery and extend the cycle life.

[0146] It can be seen from Examples 1 to 4 and Comparative Example 1 that in the negative electrode sheet of the present application, the coating rate of the coating layer is within a specific range, which can further improve the tensile modulus and tensile strength of the electrode sheet and increase the cycle life of the secondary battery.

[0147] It can be seen from Examples 1 to 4 and Comparative Examples 1 and 2 that in the negative electrode sheet of the present application, the thickness of the coating layer is within a specific range, which can further improve the tensile modulus and tensile strength of the electrode sheet and increase the cycle life of the secondary battery.

[0148] It can be seen from Examples 1 to 4 and Comparative Examples 3 and 4 that in the negative electrode sheet of the present application, the mass ratio of the modified nano-negative electrode material to the reduced graphene oxide is within a specific range, which can form a thin film sheet well and improve the capacity and cycle life of the secondary battery.

[0149] <Example 10>, <Example 11>, <Comparative Example 6>, <Comparative Example 7>

[0150] In Examples 10 and 11, and Comparative Examples 6 and 7, except for changing the specific conditions in step (1) as shown in Table 4, the same preparation method as in Example 3 was adopted to obtain negative electrode sheets.

[0151] [Table 4]

[0152]

[0153] As can be seen from Table 3, from Examples 3, 10, 11, Comparative Examples 6, 7, it can be known that by controlling the ultrasonic and stirring treatment time in step (1) within a specific range, the coating rate of the coating layer can be increased, and the tensile modulus and tensile strength of the pole piece can be increased. When the ultrasonic and stirring treatment is within an appropriate range, on the one hand, the core can be well coated to obtain a higher tensile modulus and tensile strength; on the other hand, the thickness of the coating layer can be prevented from being too thick, thereby not affecting the overall energy density of the secondary battery.

[0154] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode sheet, wherein: Including reduced graphene oxide sheets and modified nano negative electrode materials, The modified nanometer negative electrode material comprises: Kernel; and A coating layer coated on the surface of the core, The molecular formula of the core is A x B y , wherein A is at least one selected from antimony, molybdenum, and silicon, B is at least one selected from sulfur, selenium, and oxygen, 1≤x≤3, 1≤y≤4, The coating layer includes polydopamine; The mass ratio of the core to the coating layer is 2:1 to 1:

3.

2. The negative electrode sheet according to claim 1, wherein: The coating rate of the coating layer is above 80%.

3. The negative electrode sheet according to claim 1, wherein: The coating layer has a thickness of 15 nm to 42 nm.

4. The negative electrode sheet according to any one of claims 1 to 3, wherein: The mass ratio of the modified nanometer negative electrode material to the reduced graphene oxide is 1:2 to 1:

1.

5. The negative electrode sheet according to any one of claims 1 to 3, wherein: The tensile modulus of the negative electrode plate is 175 GPa to 700 GPa.

6. The negative electrode sheet according to any one of claims 1 to 3, wherein: The tensile strength of the negative electrode plate is 3.4 MPa to 9.3 MPa.

7. A method for preparing a negative electrode sheet, wherein: The process comprises the following steps (1) to (3): Step (1): homogenizing the core material and dopamine in a tris buffer, wherein the mass ratio of the core material to the dopamine is 2:1 to 1:3; Step (2): dispersing the product of step (1) in a graphene oxide solution, reducing it at a first temperature and then performing vacuum filtration, pre-freezing the obtained filter membrane at a second temperature, and freeze-drying the pre-frozen material at a third temperature to obtain a porous film; Step (3): calcining the thin film obtained in step (2) under an inert and / or reducing atmosphere to obtain the negative electrode sheet.

8. The method for preparing a negative electrode sheet according to claim 7, wherein: In the step (1), the homogenization treatment is carried out by ultrasonication and stirring for 6 hours to 24 hours.

9. The method for preparing a negative electrode sheet according to claim 8, wherein: In the step (2), the first temperature is 80° C. to 100° C., and the reduction time is 2 min to 30 min.

10. The method for preparing a negative electrode sheet according to any one of claims 7 to 9, wherein: In the step (2), the second temperature is -200°C to -80°C, the third temperature is -30°C to -50°C, and the freeze-drying time is 16h to 48h.

11. The method for preparing a negative electrode sheet according to any one of claims 7 to 9, wherein: In the step (3), calcination is performed at 100° C. to 550° C. for 0.5 h to 5 h.

12. A secondary battery, wherein: The secondary battery comprises the negative electrode sheet according to any one of claims 1 to 6 or the negative electrode sheet prepared by the preparation method according to any one of claims 7 to 11.

13. A battery module, wherein: The battery module includes the secondary battery according to claim 12.

14. A battery pack, wherein: The battery pack includes the battery module according to claim 13.

15. An electrical device, wherein: The electric device includes at least one selected from the group consisting of the secondary battery of claim 12 , the battery module of claim 13 , and the battery pack of claim 14 .

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