Battery diaphragm as well as preparation method and application thereof

Abstract

The invention provides a battery diaphragm and a preparation method and application thereof, the battery diaphragm comprises a base membrane and an organic polymer coating loaded on at least one side of the base membrane, the parameter Y of the organic polymer coating is below 0.8, the calculation formula of the Y is as shown in formula 1, Y = (Rq * P) / H formula 1, in the formula 1, Rq is the root-mean-square height of the organic polymer coating, and H is the root-mean-square height of the organic polymer coating. The unit is [mu] m, P is the porosity of the organic polymer coating and the unit is%, and H is the thickness of the battery diaphragm and the unit is [mu] m. The diaphragm disclosed by the invention has good pole piece bonding force and electrolyte wettability, so that the deformation resistance and ion transmission capacity of a battery cell are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and particularly relates to a battery separator, a preparation method thereof, and an application thereof. Background Art

[0002] As an important component of a battery (such as a lithium-ion battery), the separator plays a key role in improving the safety performance of the battery during use and cycling. In the entire battery cell system, the separator not only needs to have good electrochemical properties, such as electrochemical stability and lithium-ion conductivity, but also needs to have excellent non-electrochemical properties, such as adhesiveness, a relatively high porosity with high thermal stability, and a uniform pore size distribution, etc.

[0003] To meet the performance requirements of the battery cell for the separator, the mainstream solution is to coat and modify the separator. Among them, the coating of inorganic ceramic particles such as alumina and boehmite can enhance the heat resistance of the separator, while the coating of organic polymer materials such as PVDF (polyvinylidene fluoride) can improve the adhesiveness to the electrode sheet. The current main separator coating processes include microgravure coating, extrusion coating, knife coating, and immersion coating. In the prior art, the coating process of organic polymers such as PVDF still has deficiencies such as uneven pore size distribution of the coating, which is extremely likely to induce an uneven deposition / dissolution process of lithium ions, seriously affecting the long cycle life of the battery.

[0004] There is a need to develop a coated separator that ensures the adhesiveness between the separator and the electrode sheet and the wettability of the electrolyte, and at the same time takes into account improving the anti-deformation ability and ion transport ability of the battery cell. Summary of the Invention

[0005] The present invention provides a battery separator, a preparation method thereof, and an application thereof. The separator has good adhesiveness to the electrode sheet and electrolyte wettability to improve the anti-deformation ability and ion transport ability of the battery cell.

[0006] The present invention provides a battery separator, the battery separator includes a base film, and an organic polymer coating loaded on at least one side of the base film, and the parameter Y of the organic polymer coating is 8 or less. The calculation formula of Y is as shown in Formula 1:

[0007] Y = (R q × P) / H Formula 1

[0008] In Formula 1, R q is the root mean square height of the organic polymer coating, with the unit of μm, P is the porosity of the organic polymer coating, with the unit of %, and H is the thickness of the battery separator, with the unit of μm.

[0009] Optionally, the root mean square height R q of the organic polymer coating is greater than 0 and less than or equal to 0.5 μm.

[0010] Optionally, the maximum height R of the organic polymer coating z is greater than 0 and less than or equal to 3 μm.

[0011] Optionally, the porosity of the organic polymer coating is 40% to 50%; and / or, the thickness of the organic polymer coating is 0.5 to 5 μm; and / or, the average pore size of the organic polymer coating is 34 to 50 nm.

[0012] Optionally, the organic polymer coating comprises a fluoropolymer.

[0013] Optionally, the weight-average molecular weight of the fluoropolymer is 600,000 to 1,000,000 g / mol; and / or, the fluoropolymer comprises at least one of polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-tetrafluoroethylene, polyvinylidene fluoride-co-trifluoroethylene, polyvinylidene fluoride-co-trichlorofluoroethylene, polyvinylidene fluoride-co-vinyl fluoride, and polyvinylidene fluoride-co-trichloroethylene.

[0014] Optionally, the thickness of the battery separator is 4 to 25 μm; and / or, the adhesion of the battery separator is 20 gf / 25 mm or more; and / or, the ionic conductivity of the battery separator is 0.75 mS / cm to 1 mS / cm; and / or, the air permeability value of the battery separator is 100 to 500 Sec / 100 ml.

[0015] The present invention also provides a method for preparing a battery separator as described above, comprising: mixing a raw material system comprising an organic polymer and a first organic solvent to obtain a coating slurry; coating the coating slurry on at least one surface of a base film, then placing it in a coagulation bath, and then taking it out for drying to obtain the battery separator; wherein, the coagulation bath comprises a phase separation agent, an inorganic salt, and a second organic solvent, and in the coagulation bath, the mass fraction of the phase separation agent is 50% to 100%, the mass fraction of the inorganic salt is 0.1% to 10%, and the mass fraction of the second organic solvent is 0 to 49.9%.

[0016] Optionally, it further includes: coating the coating slurry on at least one surface of the base film, then performing pre-treatment at 20-60°C, then placing it in the coagulation bath, and then taking it out for drying to obtain the battery separator; and / or, the mass fraction of the organic polymer in the coating slurry is 7%-15%; and / or, the first organic solvent includes at least one of N-methylpyrrolidone, dimethylacetamide, and dimethylformamide; and / or, the second organic solvent respectively includes at least one of N-methylpyrrolidone, dimethylacetamide, and dimethylformamide; and / or, the phase separation agent includes at least one of water, methanol, ethanol, propanol, butanol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol; and / or, the inorganic salt includes at least one of sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, lithium oxalate, lithium hexafluorophosphate, and lithium tetrafluoroborate.

[0017] The present invention also provides a battery, which includes the battery separator as described above or the battery separator obtained according to the preparation method as described above.

[0018] The present invention provides a battery separator, its preparation method and application. The battery separator (coated separator or coated and modified separator) has good adhesion to the electrode sheet. The good adhesion effect can effectively improve the stiffness of the bare battery cell and enhance the anti-deformation ability of the battery cell. The strong adhesion between the separator and the electrode sheet can also inhibit the separator-electrode sheet separation phenomenon during the battery cycling process and improve the cycle life of the battery. The above battery separator also has good wettability with the electrolyte, which not only improves the liquid injection speed during the battery cell preparation process but also endows the separator with good lithium ion transmission ability. More importantly, the above battery separator takes into account the performance of a narrow width of the coating pore size distribution range, that is, the organic coating also has the characteristics of being uniform and having a narrow pore size distribution range, making the lithium ion deposition and dissolution processes more uniform, effectively improving the long cycle life of the battery and effectively solving the defects in the prior art. Description of the Drawings

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0020] Figure 1 It is the scanning electron microscope image of the microscopic morphology of the polyethylene porous base film in each example and comparative example (magnification is 20K);

[0021] Figure 2 It is the scanning electron microscope image of the microscopic morphology of the battery separator (coating side) in Example 4 (magnification is 20K);

[0022] Figure 3 Scanning electron microscope image (magnification: 20K) of the microscopic morphology of the battery separator (coated side) of Example 19;

[0023] Figure 4 Scanning electron microscope image (magnification: 20K) of the microscopic morphology of the battery separator (coated side) of Example 22;

[0024] Figure 5 Surface roughness morphology map of the polyethylene porous base film in each example and comparative example;

[0025] Figure 6 Surface roughness morphology map of the battery separator (coated side) of Example 4;

[0026] Figure 7 Surface roughness morphology map of the battery separator (coated side) of Example 19. Detailed Description of the Invention

[0027] To enable those skilled in the art to better understand the solution of the present invention, the present invention will be further described in detail below. The following specific embodiments are only used to describe the principles and features of the present invention, and the examples given are only used to explain the present invention, not to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0028] In the prior art, organic polymer coating processes such as polyvinylidene fluoride coating still have deficiencies such as uneven pore size distribution of the coating, which can easily induce an uneven deposition / dissolution process of lithium ions and seriously affect the long cycle life of the battery.

[0029] To overcome the defects in the prior art, an embodiment of the present invention provides a battery separator, which includes a base film and an organic polymer coating loaded on at least one side of the base film. The parameter Y of the organic polymer coating is 8 or less, and the calculation formula of Y is shown in Formula 1:

[0030] Y = (R q × P) / H Formula 1

[0031] In Formula 1, R q is the root mean square height of the organic polymer coating, with the unit of μm, P is the porosity of the organic polymer coating, with the unit of %, and H is the thickness of the battery separator, with the unit of μm.

[0032] According to research and analysis: By synergistically controlling the overall height deviation, porosity, and thickness in the battery separator of the organic polymer coating to meet the parameter Y of 8 or less, it helps to improve the adhesion between the organic polymer coating of the above battery separator and the electrode sheet. A good adhesion effect can effectively enhance the stiffness of the battery cell and the ability of the battery cell to resist deformation. The strong adhesion between the separator and the electrode sheet can also inhibit the separator-electrode sheet separation phenomenon that occurs during the battery cycle, improving the cycle life of the battery. Moreover, the above battery separator has good electrolyte wettability, which not only improves the liquid injection speed during the battery cell preparation process but also endows the separator with good lithium-ion transmission ability. It is speculated that this may be because when the battery separator meets the parameter Y of 8 or less, the surface tension of the organic polymer coating film is significantly reduced, and its thickness ratio in the battery separator can not only achieve an improvement in ionic conductivity but also achieve good adhesion and provide good stiffness for the battery cell.

[0033] In some embodiments, the root mean square height R of the above organic polymer coating q is greater than 0 and less than or equal to 0.5 μm. Exemplarily, the root mean square height R of the organic polymer coating q can be 0.1, 0.2, 0.3, 0.4, 0.5 μm or a range composed of any two of them. By controlling the root mean square height of the organic polymer coating to meet the above range, it helps to make the overall fluctuation amplitude of the coating surface more appropriate, which is beneficial to further balance the sufficient contact area and roughness between the coating and the electrode sheet, thereby improving the adhesion between the solid electrolyte separator and the electrode sheet and the electrolyte wetting performance, and further improving the battery cell's ability to resist deformation and ionic transmission ability.

[0034] R z is the maximum height value of the organic polymer coating, with the unit of μm.

[0035] In some embodiments, the maximum height R of the organic polymer coating z is greater than 0 and less than or equal to 3 μm. By controlling the maximum height of the organic polymer coating to meet the above range, the extreme peaks and valleys on the coating surface are in a good fluctuation range, which helps to further improve the adhesion between the solid electrolyte separator and the electrode sheet and provide a certain electrolyte absorption and retention point, and further improve the battery cell's ability to resist deformation and ionic transmission ability.

[0036] Exemplarily, the maximum height R of the organic polymer coating z can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0 μm or a range composed of any two of them.

[0037] In some embodiments of the present invention, R q and R z can be tested according to the provisions of the standard ISO25178-2:2012. Specifically, a 3D laser confocal microscope (LEXT OLS5100) can be used for measurement. For example, a 100× objective lens can be used for measurement.

[0038] It can be understood that the above-mentioned organic polymer coating is a porous membrane with a uniformly distributed pore structure.

[0039] In some embodiments, the porosity of the above-mentioned organic polymer coating is 40% to 50%. By controlling the porosity of the organic polymer coating to meet the above range, it helps to ensure that the coating has a suitable bonding part and void part, and cooperate with the surface roughness of the coating to further improve the adhesion between the solid electrolyte separator and the electrode sheet and the electrolyte wetting performance, and further improve the anti-deformation ability and ion transport ability of the battery cell.

[0040] Exemplarily, the porosity of the organic polymer coating can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50% or a range composed of any two of them.

[0041] In some embodiments, the average pore diameter of the organic polymer coating is 34 to 50 nm. By controlling the pore size distribution of the organic polymer coating to meet the above range, a suitable pore diameter helps to further improve the liquid absorption and retention performance, further enhance the electrolyte wetting performance, and further improve the ion transport ability.

[0042] Exemplarily, the average pore diameter of the organic polymer coating can be 34, 35, 40, 45, 50 nm or a range composed of any two of them.

[0043] In some embodiments, the thickness of the above-mentioned organic polymer coating is 0.5 to 5 μm. By controlling the thickness of the organic polymer coating to meet the above range, it helps to further ensure sufficient electrolyte wettability and adhesiveness while reducing the internal resistance, and further improve the ion transport ability.

[0044] Exemplarily, the thickness of the organic polymer coating can be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.5, 4.0, 4.5, 5 μm or a range composed of any two of them.

[0045] In some embodiments, the areal density of the organic polymer coating is not particularly limited and can be selected from organic polymer coatings with any areal density. For example, considering the battery impedance and ion transport ability, it is preferably 0.5 to 5 g / m 2 .

[0046] Exemplarily, the areal density of the organic polymer coating can be 0.5, 1, 2, 3, 4, 5 g / m 2 or the range composed of any two of them.

[0047] In some embodiments, the above-mentioned organic coating includes a fluoropolymer.

[0048] In the organic coating formed by the fluoropolymer, the polymer exists in a network form, and part of the polymer accumulates to form convex granular shapes and are interconnected through the network structure. This organic coating in the form of particle accumulation can maintain a strong bonding effect with the electrode sheet, and also helps to improve the wettability of the battery separator and the electrolyte, and enhance the electrochemical performance.

[0049] The weight-average molecular weight of the above-mentioned fluoropolymer can be 600,000 to 1,000,000 g / mol, such as 600,000 g / mol, 700,000 g / mol, 800,000 g / mol, 900,000 g / mol, 1,000,000 g / mol or the range composed of any two of them. It helps to further improve the adhesion between the solid electrolyte separator and the electrode sheet and the wettability of the electrolyte, and further improve the anti-deformation ability and ion transport ability of the battery cell.

[0050] In some embodiments, the weight-average molecular weight of the fluoropolymer can be obtained by analyzing gel permeation chromatography (GPC) tests.

[0051] Specifically, the above-mentioned fluoropolymer can include at least one of polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-tetrafluoroethylene, polyvinylidene fluoride-co-trifluoroethylene, polyvinylidene fluoride-co-trifluorochloroethylene, polyvinylidene fluoride-co-vinyl fluoride, and polyvinylidene fluoride-co-trichloroethylene.

[0052] In the embodiments of the present invention, the above-mentioned fluoropolymer can be obtained by conventional methods, such as commercially available or self-made by conventional methods. When self-making the above-mentioned fluoropolymer, the molecular weight can be regulated by conventional methods, and no special limitation is made thereto.

[0053] Compared with polyolefin materials, the fluoropolymer has good affinity and wettability for the electrolyte. This not only improves the liquid injection speed during the preparation of the battery cell, but also endows the separator with good lithium ion transport ability. In addition, it helps to increase the bonding strength between the separator and the electrode sheet.

[0054] The embodiments of the present invention effectively solve the problem of uneven pore size distribution in the coating of fluoropolymer separators in the prior art.

[0055] In some embodiments, the thickness of the above battery separator is 4-25 μm. This helps to further improve the adhesion between the solid electrolyte separator and the electrode and the electrolyte wetting performance, and further improve the anti-deformation ability and ion transport ability of the battery cell.

[0056] Exemplarily, the thickness of the battery separator can be 4, 5, 10, 15, 20, 25 μm or any range composed of any two of them.

[0057] In some embodiments, the adhesion of the battery separator is above 20 gf / 25 mm.

[0058] In some embodiments, the ionic conductivity of the battery separator is 0.75 mS / cm - 1 mS / cm.

[0059] In some embodiments, the air permeability value of the battery separator is 100 - 500 Sec / 100 ml.

[0060] The ionic conductivity and air permeability value of the battery separator can be obtained by existing test methods. Specifically, it can be tested with reference to the standard GB-T 36363-2018 "Polyolefin Separators for Lithium-Ion Batteries".

[0061] In the embodiments of the present invention, the base film can be a conventional porous separator material in the art. For example, the base film can include one or more of polymer porous membranes, fiber porous membranes, and non-woven fabrics, etc. The polymer porous membrane can include one or more of polyolefin porous membranes, polyimide porous membranes, polyvinylidene fluoride porous membranes, polyethylene terephthalate (PET) porous membranes, etc. The polyolefin porous membrane includes, for example, polyethylene porous membrane and / or polypropylene porous membrane.

[0062] It can be understood that the above base film is a porous membrane with a uniformly distributed pore structure. The porosity, pore size, and thickness of the base film are not particularly limited. For example, the average pore size can be 5 - 100 nm, the porosity is 20% - 80%, and the base film thickness can be 1 - 50 μm

[0063] For the consideration of ensuring higher ionic conductivity and mechanical strength, preferably, the average pore size of the base film can be 25 nm - 50 nm, and the porosity of the base film can be 30% - 60%.

[0064] In some embodiments, for the consideration of lower battery impedance and mechanical strength, preferably, the thickness of the above base film can be selected from 3 - 20 μm.

[0065] In some embodiments, the average pore size, porosity, and thickness of the base film can be obtained by existing testing methods. Specifically, the porosity and thickness can be obtained by referring to the standard GB-T 36363-2018 "Polyolefin Separator for Lithium-Ion Batteries" for testing; the average pore size can be calculated from the pore size distribution measured using a capillary flow porometer (CFP method). For example, first, wet the separator to be measured with a wetting agent such as galwick solution, and then gradually increase the air pressure on one surface of the substrate. At this time, when the applied air pressure becomes greater than the capillary attraction of the wetting agent present in the pores, the wetting agent blocking the pores is pushed out, and the pore size and distribution are measured based on the pressure and flow rate at the time of being pushed out, thereby enabling confirmation of the average pore size.

[0066] An embodiment of the present invention further provides a method for preparing the above battery separator, including: mixing a raw material system including an organic polymer and a first organic solvent to obtain a coating slurry; coating the coating slurry on at least one surface of the base film, and then placing it (such as immersing it) in a coagulation bath for phase inversion and drying to obtain a battery separator; wherein, the coagulation bath includes a phase separation agent, an inorganic salt, and a second organic solvent. In the coagulation bath, the mass fraction of the phase separation agent accounts for 50% to 100%, the mass fraction of the inorganic salt accounts for 0.1% to 10%, and the mass fraction of the second organic solvent accounts for 0 to 49.9%.

[0067] According to research and analysis, the above coagulation bath acts on the coated coating slurry, which helps to form a composite separator with parameter Y of 8 or less, and then obtain the battery separator of the embodiment of the present invention.

[0068] It can be understood that the mass fraction of the phase separation agent in the coagulation bath is 50% to 100%, the mass fraction of the inorganic salt is 0.1% to 10%, and the mass fraction of the second organic solvent is 0 to 49.9%, which means that the mass percentage content of the phase separation agent in the coagulation bath is 50% to 100%, the mass percentage content of the inorganic salt in the coagulation bath is 0.1% to 10%, and the mass percentage content of the second organic solvent in the coagulation bath is 0, 1%, 5%, 10%, 20%, 30%, 40%, 45%, 49%, 49.9% or any range composed of any two of them.

[0069] Exemplarily, in the coagulation bath, the mass fraction of the phase separation agent is 50%, 60%, 70%, 80%, 90%, 100% or any range composed of any two of them, and the mass fraction of the inorganic salt is 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any range composed of any two of them.

[0070] The inorganic salts may include sodium salts, potassium salts, and lithium salts. For example, the inorganic salts may include at least one of sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, lithium oxalate, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), etc.

[0071] Preferably, the inorganic salts include lithium salts (i.e., inorganic salts containing lithium ions), such as at least one of lithium oxalate, lithium hexafluorophosphate (LiPF6), and lithium tetrafluoroborate (LiBF4). Thus, the remaining inorganic salts can replenish lithium for the battery, which is beneficial to further improving the lithium ion transport performance.

[0072] As described above, in the above coagulation bath, the mass fraction of the second organic solvent is less than 50 wt%.

[0073] In some embodiments, the mass fraction of the organic polymer in the coating slurry is 7% - 15%, that is, the mass fraction of the organic polymer in the raw material system is 7% - 15%.

[0074] Exemplarily, the mass fraction of the organic polymer in the coating slurry is 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or a range composed of any two of them.

[0075] Both the first organic solvent and the second organic solvent can be independently selected from good solvents that can dissolve fluoropolymers.

[0076] In some embodiments, the first organic solvent includes at least one of N-methylpyrrolidone, dimethylacetamide, and dimethylformamide.

[0077] In some embodiments, the second organic solvent includes at least one of N-methylpyrrolidone, dimethylacetamide, and dimethylformamide.

[0078] In some embodiments, the phase separation agent includes at least one of water, methanol, ethanol, propanol, butanol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol. Preferably, the phase separation agent includes water.

[0079] In some embodiments, the above coating method may include one or more of microgravure coating, extrusion coating, knife coating, and immersion coating.

[0080] The embodiments of the present invention do not particularly limit the temperature of the above coagulation bath or the temperature for the phase inversion process of placing the base film coated with the coating slurry in the coagulation bath. For example, it can be selected from 25 - 50°C.

[0081] The embodiments of the present invention do not particularly limit the phase inversion time in the above coagulation bath, as long as the coating slurry can be phase-separated and cured.

[0082] In the embodiments of the present invention, there is no special limitation on the drying temperature, as long as the liquid remaining on the surface of the separator removed from the coagulation bath can be volatilized sufficiently. For example, the drying temperature can be 50 to 80 °C, such as 50, 60, 70, 80 °C or the range composed of any two of them.

[0083] In order to further improve the effect of the coagulation bath, before placing the base film coated with the coating slurry into the coagulation bath, it can be pretreated.

[0084] In some embodiments, the method for preparing the battery separator further includes: coating the coating slurry on at least one surface of the base film, then performing pretreatment at 20 to 60 °C, then placing it into the coagulation bath, and then taking it out for drying to obtain the battery separator.

[0085] In some embodiments, the pretreatment temperature can be 20 to 60 °C, such as 20, 30, 40, 50, 55, 60 °C or the range composed of any two of them. There is no special limitation on the pretreatment time in the embodiments of the present invention. For example, it can be 2 to 180 seconds.

[0086] Performing pretreatment before the coated separator enters the coagulation bath is more conducive to jointly controlling the surface roughness and pore structure of the coating in cooperation with the inorganic salt content in the coagulation bath, and obtaining a composite separator that meets the above requirements.

[0087] Generally, the above drying process and pretreatment can be operated in an oven.

[0088] The embodiments of the present invention also provide a battery, which includes the above battery separator or the battery separator obtained according to the above preparation method.

[0089] This battery has the corresponding advantages as the above battery separator, which will not be elaborated here.

[0090] Specifically, the above battery can be a liquid battery, a gel battery or a semi-solid battery.

[0091] Generally, a battery includes an electric core and a housing for encapsulating the electric core. The electric core includes a positive electrode sheet, a separator and a negative electrode sheet. The separator is located between the positive electrode sheet and the negative electrode sheet, used to separate the positive electrode sheet and the negative electrode sheet to prevent them from contacting and short-circuiting. At the same time, the separator is also used to allow active ions such as lithium ions to pass through, so that the active ions such as lithium ions can be inserted and extracted between the positive and negative electrodes to realize the charge and discharge process of the battery.

[0092] In the embodiments of the present invention, the electric core can be encapsulated with conventional housing materials in the art. The housing includes soft packaging materials such as aluminum-plastic films, but is not limited thereto.

[0093] Generally, the positive electrode sheet includes a positive electrode current collector and a positive electrode coating on at least one surface of the positive electrode current collector. Specifically, the positive electrode coating can be provided on one surface of the positive electrode current collector, or on the opposite surfaces in the thickness direction of the positive electrode current collector (i.e., the front and back surfaces of the positive electrode current collector).

[0094] Specifically, the positive electrode coating (positive electrode active material layer) includes materials such as positive electrode active substances, conductive agents, and binders. In addition, the positive electrode coating can also include a solid electrolyte. These materials in the positive electrode coating can all be conventional materials in the art. For example, the positive electrode active substances can include one or more of lithium cobaltate, lithium iron phosphate, and ternary materials. The ternary materials can include nickel-cobalt-manganese ternary materials and / or nickel-cobalt-aluminum ternary materials; the conductive agent can include conductive carbon, specifically, it can include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; the binder can include one or more of polyvinylidene fluoride (PVDF), polyvinylidene difluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polymers containing ethylene oxide, polyvinylpyrrolidone, and polyurethane.

[0095] Among them, when the positive electrode coating can also include a solid electrolyte, the solid electrolyte in the positive electrode coating and the solid electrolyte material in the separator can be the same or different.

[0096] In some embodiments, in the positive electrode coating, the mass percentage content of the positive electrode active substance can be 75% - 90%, the mass percentage content of the solid electrolyte can be 10% - 25%, the mass percentage content of the conductive agent can be 0.2% - 1.0%, and the mass percentage content of the binder can be 0.5% - 1.5%.

[0097] Embodiments of the present invention can use conventional positive electrode current collectors in the art. For example, the positive electrode current collector includes aluminum foil.

[0098] In embodiments of the present invention, the positive electrode sheet can be prepared by a conventional coating method in the art. Specifically, components for forming the positive electrode coating such as positive electrode active substances, solid electrolytes, conductive agents, and binders can be dispersed in a third solvent. The third solvent includes, for example, N-methylpyrrolidone (NMP) to prepare a positive electrode slurry; the positive electrode slurry is coated on the surface of the positive electrode current collector, and after processes such as drying and rolling, the positive electrode sheet is obtained. Among them, the involved coating, drying, rolling and other processes are conventional operations for preparing the positive electrode sheet by the coating method, and no special limitations are made thereto.

[0099] In addition, the negative electrode sheet includes a negative electrode current collector and a negative electrode coating on at least one surface of the negative electrode current collector. Specifically, the negative electrode coating can be provided on one surface of the negative electrode current collector, or on the opposite surfaces in the thickness direction of the negative electrode current collector are respectively provided with negative electrode coatings.

[0100] Specifically, the negative electrode coating may include materials such as negative electrode active materials, conductive agents, and binders. These materials can be conventional materials in the art. For example, the negative electrode active materials may include one or more of silicon-based materials, silicon oxy-based materials, silicon-carbon-based materials, graphite, metallic lithium, lithium-indium alloy materials, etc.; the conductive agents may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, carbon fibers; the binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polyamideimide, polyvinyl alcohol, sodium polyacrylate.

[0101] The embodiments of the present invention may use a conventional negative electrode current collector in the art. For example, the negative electrode current collector includes copper foil.

[0102] In the embodiments of the present invention, the negative electrode sheet can be prepared by a conventional method in the art. For example, it can be prepared by a coating method. Specifically, components for forming the negative electrode coating such as negative electrode active materials, conductive agents, and binders can be dispersed in a fourth solvent. The fourth solvent includes, for example, water (specifically deionized water) to prepare a negative electrode slurry, and then it is coated on the surface of the negative electrode current collector. After processes such as drying and rolling, the negative electrode sheet is obtained.

[0103] Generally, when the battery is a semi-solid battery, the battery further includes an electrolyte. The embodiments of the present invention may use a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which specifically may include organic solvents and electrolyte salts. The organic solvents may include one or more of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), vinylene carbonate (VC), and propylene carbonate (PC). The electrolyte salts may include lithium salts, and the lithium salts may include, for example, lithium hexafluorophosphate (LiPF6), etc., but are not limited thereto.

[0104] In the embodiments of the present invention, the battery can be prepared by a conventional method in the art. For example, taking the preparation process of a semi-solid battery as an example, its preparation process may include: assembling a positive electrode sheet, a separator, and a negative electrode sheet into an electric core, then encapsulating it with a housing, and after processes such as liquid injection (injecting the electrolyte into the housing) and formation, a semi-solid battery is obtained. The processes involved are all conventional preparation processes for semi-solid batteries, and no special restrictions are imposed thereon. Among them, in the case where an organic polymer coating is coated on one side of the battery separator, the side of the battery separator provided with the organic polymer coating can face the negative electrode.

[0105] The present invention will be further described below through specific examples and comparative examples. Unless otherwise specified, the reagents, materials, and instruments used below are all conventional reagents, conventional materials, and conventional instruments, which can be obtained commercially, and the reagents and materials involved can also be synthesized by conventional synthesis methods.

[0106] Example 1

[0107] The battery of this example is prepared by a method including the following steps:

[0108] 1) Preparation of battery separator

[0109] Mix NaCl salt and deionized water to obtain an aqueous NaCl solution; mix the aqueous NaCl solution and N-methylpyrrolidone to obtain a coagulation bath. The mass percentage of water in the coagulation bath is 95%, and the mass fraction of NaCl salt is 2%;

[0110] Mix polyvinylidene fluoride (PVDF) and N-methylpyrrolidone with a mass ratio of 1:9, stir well at 30 °C until completely dissolved, and then wait for it to cool to room temperature to obtain a coating slurry; among them, the weight-average molecular weight of PVDF is 1,000,000 g / mol;

[0111] Coat the coating slurry on both side surfaces of a base film with a thickness of 9 μm (polyolefin porous base film, Xingyuan Material, SW509C+), and the single-sided coating thickness is 3 μm; transfer the base film coated with the coating slurry to an oven at 25 °C for a pretreatment for 2 seconds, then immerse it completely in the above-mentioned coagulation bath, carry out a phase inversion process at 25 °C for 1 min, and then dry it at 65 °C for 2 min to obtain a battery separator (PVDF-coated separator) with organic polymer coatings loaded on both side surfaces.

[0112] 2) Preparation of battery

[0113] Stack the positive electrode sheet, battery separator, and negative electrode sheet to obtain an electrolytic assembly, place the electrode assembly in an aluminum-plastic film, and seal it to obtain a battery;

[0114] Among them, the positive electrode sheet includes an aluminum foil and a positive electrode active layer provided on the surface of the aluminum foil. The positive electrode active layer includes lithium cobaltate, conductive agent Super P, and binder PVDF. The mass ratio of lithium cobaltate, conductive agent, and binder is 96:2:2; the negative electrode sheet includes a copper foil and a negative electrode active layer provided on the surface of the copper foil. The negative electrode active layer includes silicon-doped graphite, conductive agent Super P, and binder PAA. The mass ratio of silicon-doped graphite, conductive agent, and binder is 95:2:3; the electrolyte includes lithium hexafluorophosphate (LiPF6), EC, DEC, and DMC. In the electrolyte, the concentration of lithium hexafluorophosphate (LiPF6) is 1M, and the volume ratio of EC, DEC, and DMC is 1:1:1.

[0115] Referring to Example 1, the batteries of Examples 2 to 25 and Comparative Examples 1 to 2 were prepared. Among them, the types of fluoropolymers, the weight-average molecular weights of fluoropolymers, the mass percentages of fluoropolymers in the coating slurry, the mass percentage of water in the coagulation bath, the addition amount of salt in the coagulation bath, the phase inversion temperature, the pretreatment temperature, the coating position, etc. of each example and comparative example are summarized in Table 1. The thickness of the base film, the average pore diameter of the base film, the porosity of the base film, Y value, Rq, Rz, the porosity of the organic polymer coating, the thickness of the battery separator, the single-sided thickness of the organic coating, the average pore diameter of the organic polymer coating, the single-sided surface density of the organic polymer coating, etc. of each example and comparative example were calculated or tested and summarized in Table 2: The differences between Examples 2 to 25 and Comparative Examples 1 to 2 and Example 1 are shown in Tables 1 and 2. Except for the differences shown in Tables 1 and 2, the remaining conditions are the same as those in Example 1.

[0116] Table 1

[0117]

[0118]

[0119] Note: In the case of single-sided coating, the side of the battery separator with the organic polymer coating faces the negative electrode.

[0120] Table 2

[0121]

[0122]

[0123] Test Example

[0124] The following parameters of each example and comparative example were tested respectively:

[0125] 1) Test of the adhesion force (adhesion performance) of the battery separator

[0126] The adhesion of the battery separator can be tested by the following method: cut the battery separator into test strips with a width of 25 mm and a length of 60 mm, and cut the negative electrode sheet into test strips with a width of 25 mm and a length of 40 mm; use 3M tape to bond the coated side of the cut separator test strip and the electrode sheet, and then sandwich them between two white paper strips (the size of the white paper strips is larger than the size of the separator test strip), and pressurize (hot press) at 60°C and 1MPa for 1 min, and then naturally cool at room temperature, peel off the separator test strip and the electrode sheet to form a clamping part, and put the hot-pressed separator strip and the negative electrode sheet into the clamp of the stretching machine for a 180° peeling test, with a test speed of 300mm / min and a gauge length of 100mm.

[0127] 2) Ionic conductivity test

[0128] It can be obtained by testing with reference to the standard GB-T 36363-2018 "Polyolefin separator for lithium-ion batteries". The composition of the electrolyte used includes a lithium salt LiPF6 concentration of 1 mol / L, and the solution includes EC, DMC, and DEC in a volume ratio of 1:1:1 (Vol%).

[0129] 3) 80-cycle capacity retention rate

[0130] The test was carried out according to the test method specified in the national standard GB / T 31467-2023 "Electrical Performance Test Methods for Lithium-ion Power Battery Packs and Systems for Electric Vehicles". The charge and discharge rate selected by the present invention was 1C and the battery cycle temperature was 25°C.

[0131] 4) Air permeability of battery separator: It can be obtained by testing in accordance with the standard GB-T 36363-2018 "Polyolefin separator for lithium-ion batteries".

[0132] 5) Micromorphology characterization: The morphology of the diaphragm is characterized by scanning electron microscopy (SEM). The specific method is tested in accordance with the industry standard JY / T 0584-2020 "General Rules for Scanning Electron Microscope Analysis Methods".

[0133] Figure 1 is a scanning electron microscope (SEM) image of the microscopic morphology of the polyethylene (PE) porous base membrane used in the examples and comparative examples of the present invention, showing the microscopic morphology of the surface of the polyethylene (PE) porous base membrane; Figure 2 , Figure 3 , Figure 4 The microscopic morphology scanning electron microscope images of the battery separators (coating side) of Examples 4, 19 and 22 are shown in FIG. Figures 2 to 4 It can be seen that the surfaces of the battery separators in Examples 4, 19 and 22 of the present invention have organic polymer coatings with different pore structures.Figure 2 It can be seen that the organic polymer coating of Example 4 of the present invention has a more evenly distributed pore structure.

[0134] 6) Surface roughness morphology characterization: A 3D laser confocal microscope (LEXT OLS5100) was used for testing according to the provisions of standard ISO25178-2:2012, and the objective lens magnification was 100 times.

[0135] Figure 5 、 Figure 6 、 Figure 7 are the surface roughness morphology diagrams of the PE-based film used in the examples and comparative examples of the present invention, and the battery separators (coated side) of Example 4 and Example 19, respectively. It can be seen that the battery separators of Example 4 and Example 19 of the present invention have a roughness morphology different from that of the PE-based film surface. Among them, the roughness morphology distribution of the battery separator of Example 4 is more uniform.

[0136] Table 3 Detection results

[0137]

[0138]

[0139] It can be seen from the data of the examples and comparative examples that when the parameter Y is below 8, it helps to improve the adhesion between the organic polymer coating of the above battery separator and the electrode sheet. A good adhesion effect can effectively improve the stiffness of the battery core and enhance the ability of the battery core to resist deformation. The strong adhesion between the battery separator and the electrode sheet can also inhibit the battery separator-electrode sheet separation phenomenon that occurs during the battery cycle, improving the cycle life of the battery. Moreover, the above battery separator has good electrolyte wettability, which not only improves the liquid injection speed during the battery core preparation process but also endows the battery separator with good lithium ion transmission ability.

[0140] It can be seen from Example 4-5 and Example 25 that the root mean square height Rq of the organic polymer coating is greater than 0 and less than or equal to 0.5 μm, and the porosity of the organic polymer coating is 40% - 50%, which helps to further improve the adhesion between the organic polymer coating of the above battery separator and the electrode sheet, ionic conductivity, and capacity retention rate.

[0141] It can be seen from Examples 15-18 that the thickness of the organic polymer coating is 0.5 - 5 μm, which also has a certain improvement on its adhesion, ionic conductivity, capacity retention rate, etc.

[0142] It can be seen from Examples 19-22 that the weight average molecular weight of the fluoropolymer is 600,000 - 1,000,000 g / mol, which is beneficial to further improving the adhesion, ionic conductivity, capacity retention rate, etc.

[0143] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery separator, characterized in that, The battery separator includes a base film and an organic polymer coating loaded on at least one side of the base film. The parameter Y of the organic polymer coating is 8 or less, and the calculation formula of Y is shown in Formula 1. Y = (R q × P) / H Equation 1 In Equation 1, R q is the root mean square height of the organic polymer coating in μm, P is the porosity of the organic polymer coating in %, and H is the thickness of the battery separator in μm.

2. The battery separator according to claim 1, wherein The root mean square height R of the organic polymer coating q is greater than 0 and less than or equal to 0.5 μm.

3. The battery separator according to claim 1, wherein The maximum height R of the organic polymer coating z is greater than 0 and less than or equal to 3 μm.

4. The battery separator according to claim 1, characterized in that, The porosity of the organic polymer coating is 40% to 50%. And / or, the thickness of the organic polymer coating is 0.5 to 5 μm. And / or, the average pore size of the organic polymer coating is 34 to 50 nm.

5. The battery separator according to claim 1, wherein The organic polymer coating includes a fluoropolymer.

6. The battery separator according to claim 5, characterized in that, The weight-average molecular weight of the fluoropolymer is 600,000 to 1,000,000 g / mol. And / or, the fluoropolymer includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-tetrafluoroethylene, polyvinylidene fluoride-co-trifluoroethylene, polyvinylidene fluoride-co-trichlorofluoroethylene, polyvinylidene fluoride-co-vinyl fluoride, and polyvinylidene fluoride-co-trichloroethylene.

7. The battery separator according to claim 1, characterized in that, The thickness of the battery separator is 4 to 25 μm. And / or, the adhesion of the battery separator is 20 gf / 25 mm or more. And / or, the ionic conductivity of the battery separator is 0.75 mS / cm to 1 mS / cm. And / or, the air permeability value of the battery separator is 100 to 500 Sec / 100 ml.

8. A method for preparing the battery separator according to any one of claims 1-7, characterized in that, Comprising: Mixing a raw material system including an organic polymer and a first organic solvent to obtain a coating slurry. Coating the coating slurry on at least one side surface of the base film, then placing it in a coagulation bath, and then taking it out for drying to obtain the battery separator. Wherein, the coagulation bath includes a phase separation agent, an inorganic salt, and a second organic solvent. In the coagulation bath, the mass fraction of the phase separation agent accounts for 50% to 100%, the mass fraction of the inorganic salt accounts for 0.1% to 10%, and the mass fraction of the second organic solvent accounts for 0 to 49.9%.

9. The preparation method according to claim 8, wherein Further comprising: Coating the coating slurry on at least one side surface of the base film, then performing pretreatment at 20 to 60 °C, then placing it in the coagulation bath, and then taking it out for drying to obtain the battery separator. And / or, the mass fraction of the organic polymer in the coating slurry accounts for 7% to 15%. And / or, the first organic solvent includes at least one of N-methylpyrrolidone, dimethylacetamide, and dimethylformamide. And / or, the second organic solvent respectively includes at least one of N-methylpyrrolidone, dimethylacetamide, and dimethylformamide. And / or, the phase separation agent includes at least one of water, methanol, ethanol, propanol, butanol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol. And / or, the inorganic salt includes at least one of sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, lithium oxalate, lithium hexafluorophosphate, and lithium tetrafluoroborate.

10. A battery, characterized in that, The battery includes the battery separator according to any one of claims 1-7 or the battery separator obtained by the preparation method according to claim 8 or 9.

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