Battery diaphragm and high-capacity battery

Abstract

The battery diaphragm comprises a base membrane and a porous layer arranged on one side or two sides of the base membrane, and a thick electrode is arranged on one side, far away from the base membrane, of the porous layer, so that an exclusive channel can be created for electrolyte, and the electrolyte retention performance of the battery diaphragm is improved; therefore, the wettability of the thick electrode can be improved, the electrical performance of the battery is improved, the technical problem of poor electrolyte wettability is solved, in addition, the porous layer can increase the electrolyte retention capacity of the battery, and meanwhile, a certain buffer space can be provided for the expansive force of the battery in the circulation process, so that the battery performance can be greatly improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a battery separator and a large-capacity battery. Background Art

[0002] In related technologies, in order to improve the energy density of lithium-ion batteries, thick electrode technology can be used, that is, increasing the coating surface density to increase the capacity of a single cell, thereby increasing the energy density of a single cell and improving product competitiveness. However, as the electrode becomes thicker, the problem of poor electrolyte wetting becomes more prominent, the transmission of ions and electrons is blocked, and the electronic and ionic conductivity are reduced, which seriously affects the electrical performance of the battery. Summary of the invention

[0003] In response to the deficiencies in the prior art, the present application provides a battery separator and a large-capacity battery, which can solve the technical problem of poor electrolyte infiltration in thick electrode technology, and can also provide a certain buffer space for the expansion force of the battery during the cycle process, thereby greatly improving the battery performance.

[0004] In a first aspect, the present application provides a battery separator, which includes a base membrane and a porous layer arranged on one side or both sides of the base membrane, wherein a thick electrode is arranged on a side of the porous layer away from the base membrane.

[0005] Furthermore, in the battery separator provided in the present application, the thickness between the porous layer and the base film satisfies: b=xa; wherein, 0≤x≤1, a is the thickness of the porous layer, and b is the thickness of the base film.

[0006] Furthermore, in the battery separator provided in the present application, x satisfies: 0.2≤x≤0.5.

[0007] Furthermore, in the battery separator provided in the present application, the pore size of the porous layer is larger than the pore size of the base membrane.

[0008] Furthermore, in the battery separator provided in the present application, the positive electrode and the negative electrode on both sides of the base film are thick electrodes, and the coating surface density of the positive electrode is m1 The coating surface density of the negative electrode is m2 Satisfy between: Among them, N is the ratio of the positive electrode capacity to the negative electrode capacity per unit area, A is the gram capacity of the positive electrode active material, B is the gram capacity of the negative electrode active material, w1 is the mass ratio of the positive electrode active material at the positive electrode, and w2 is the mass ratio of the negative electrode active material at the negative electrode.

[0009] Furthermore, in the battery separator provided in the present application, a porous layer is provided on one side of the base film, and the coating surface density of the positive electrode is m1 Satisfy: ρ m1 ≤230g / m 2 .

[0010] Furthermore, in the battery separator provided in the present application, a porous layer is provided on both sides of the base film, and the coating surface density of the positive electrode is m1 Meet: 230g / m 2 ≤ρ m1 ≤320g / m 2 .

[0011] Furthermore, in the battery separator provided in the present application, N satisfies: 0 <N<1。

[0012] Furthermore, in the battery separator provided in the present application, an electrolyte is provided between the battery separator and the thick electrode; or / and,

[0013] The porous layer includes one or more of a porous layer made of nano-aluminum oxide, a porous layer made of boehmite, a porous layer made of polyvinylidene fluoride, a porous layer made of polytetrafluoroethylene, a porous layer made of polyimide, a porous layer made of polyacrylic acid, a porous layer made of polyethylene, and a porous layer made of polypropylene.

[0014] In a second aspect, the present application further provides a large-capacity battery, which includes thick electrodes and the battery separator provided in the first aspect, wherein the thick electrodes are respectively arranged on both sides of the battery separator, and an electrolyte is arranged between the thick electrodes and the battery separator.

[0015] The battery separator provided in the present application includes a base membrane and a porous layer arranged on one or both sides of the base membrane. A thick electrode is arranged on the side of the porous layer away from the base membrane, thereby creating an exclusive channel for the electrolyte and increasing the liquid retention performance of the battery separator. This can improve the wettability of the thick electrode, thereby improving the electrical performance of the battery and solving the technical problem of poor electrolyte infiltration. In addition, the porous layer can increase the liquid retention capacity of the battery, and can also provide a certain buffer space for the expansion force of the battery during the cycle, thereby greatly improving the battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 A schematic diagram of the first structure of a battery separator provided in an embodiment of the present application;

[0018] Figure 2 A second structural schematic diagram of a battery separator provided in an embodiment of the present application;

[0019] Figure 3This is an interface diagram of a battery cell without a porous layer provided in an embodiment of the present application being converted into a fully charged negative electrode sheet;

[0020] Figure 4 This is an interface diagram of a battery cell with a porous layer provided in an embodiment of the present application being converted into a fully charged negative electrode sheet;

[0021] Figure 5 This is a battery cell cycle trend diagram provided in an embodiment of the present application. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0023] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0024] It should also be understood that the terms used in this application specification are only for the purpose of describing specific embodiments and are not intended to limit the application. As used in this application specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0025] It should be further understood that the term “and / or” used in the specification and appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0026] In addition, in this application, unless otherwise clearly specified or limited in the embodiments, the terms "installed", "connected", "connected" and "fixed" etc. appearing in the embodiments should be understood in a broad sense. For example, the connection can be a fixed connection, a detachable connection, or an integrated connection. It can be understood that it can also be a mechanical connection, an electrical connection, etc.; of course, it can also be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal connection of two elements, or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific implementation situation.

[0027] Thick electrode is a widely used design strategy in lithium-ion batteries, which refers to electrodes with greater thickness in the battery, aiming to increase the energy density of the battery by increasing the active material content in the electrode. One of the main advantages of thick electrode design is that it can reduce the use of inactive materials, thereby increasing the energy density of the battery and reducing costs.

[0028] However, as the thickness of the electrode increases, the transmission path of lithium ions and electrons becomes longer, resulting in a decrease in the ion diffusion and electron conduction rates inside the electrode, which in turn affects the rate performance and cycle life of the battery.

[0029] To this end, the present application provides a battery separator and a battery, wherein the battery separator includes a base membrane and a porous layer arranged on one or both sides of the base membrane, and a thick electrode is provided on the side of the porous layer away from the base membrane, thereby creating an exclusive channel for the electrolyte and increasing the liquid retention performance of the battery separator, thereby improving the wettability of the thick electrode, thereby improving the electrical performance of the battery and solving the technical problem of poor electrolyte infiltration. In addition, the porous layer can increase the liquid retention capacity of the battery, and can also provide a certain buffer space for the expansion force of the battery during the cycle, thereby greatly improving the battery performance.

[0030] See also Figure 1 and Figure 2 , Figure 1 A schematic diagram of the first structure of a battery separator provided in an embodiment of the present application; Figure 2 This is a second structural schematic diagram of the battery separator provided in an embodiment of the present application.

[0031] like Figure 1 and Figure 2 As shown, the present application provides a battery separator, which includes a base film 110 and a porous layer 120 arranged on one side or both sides of the base film 110 , and a thick electrode is arranged on the side of the porous layer 120 away from the base film 110 .

[0032] In this embodiment, the porous layer 120 is similar to the porous layer 120 of the sponge structure, which can be arranged on one side of the base membrane 110, or on both sides of the base membrane 110. The porous layer 120 has good affinity with the electrolyte. At the same time, the porous layer 120 has a capillary effect, which can provide an exclusive channel for the electrolyte between the battery separator and the thick electrode, so as to increase the liquid retention performance of the battery separator, thereby improving the wettability of the thick electrode, improving the transmission performance of ions and electrons, avoiding the decrease in the conductivity of electrons and ions, and avoiding the decrease in the electrical performance of the battery.

[0033] Among them, the base film 110 has excellent mechanical properties, chemical stability and other characteristics, and can be a microporous film made of polyolefin materials, such as polyethylene (PE) and polypropylene (PP). At the same time, the main function of the base film 110 is to serve as a flexible support to fix and load other functional materials such as ceramic powder particles.

[0034] The thickness of the base film 110 is generally between 3 μm and 50 μm, the porosity is 30% to 60%, and the average pore size is generally between 0.01 μm and 10 μm. At the same time, the performance indicators of the base film 110 can be adjusted by a wet biaxial stretching process to meet the needs of different application scenarios. In addition, the base film 110 can also be improved by coating technology to improve its thermal stability, resistance to organic solvents, and electrolyte wettability.

[0035] The battery separator provided in the present application includes a base film 110, and a porous layer 120 arranged on one side or both sides of the base film 110. A thick electrode is provided on the side of the porous layer 120 away from the base film 110, thereby creating an exclusive channel for the electrolyte and increasing the liquid retention performance of the battery separator. This can improve the wettability of the thick electrode, thereby improving the electrical performance of the battery and solving the technical problem of poor electrolyte infiltration. In addition, the porous layer 120 can increase the liquid retention capacity of the battery, and can also provide a certain buffer space for the expansion force of the battery during the cycle, thereby greatly improving the battery performance.

[0036] In some embodiments, the thickness between the porous layer 120 and the base film 110 satisfies: b=xa; wherein 0≤x≤1, a is the thickness of the porous layer 120 , and b is the thickness of the base film 110 .

[0037] In this embodiment, the thickness between the porous layer 120 and the base film 110 satisfies: b=xa, that is, the thickness of the porous layer 120 must be smaller than the thickness of the base film 110. The thicker the porous layer 120 is, the more likely it is that the load characteristics of the battery will decrease and the energy density will decrease.

[0038] Furthermore, in some embodiments, x satisfies: 0.2≤x≤0.5.

[0039] In this embodiment, under the premise of ensuring that the energy density of the battery is not reduced and improving the wettability of the thick electrode, the thickness relationship between the porous layer 120 and the base film 110 must satisfy 0.2≤x≤0.5, that is, the ratio between the thickness of the porous layer 120 and the base film 110 must be between 0.2 and 0.5.

[0040] In some embodiments, the pore size of the porous layer 120 is larger than the pore size of the base film 110 .

[0041] Specifically, in order to make the porous layer 120 have a capillary effect and increase the liquid retention capacity of the battery, the pore size of the porous layer 120 is larger than the pore size of the base film 110, thereby increasing the liquid retention performance of the battery separator, thereby improving the wettability of the thick electrode, thereby improving the electrical performance of the battery.

[0042] In some embodiments, the positive electrode and the negative electrode on both sides of the base film are thick electrodes, and the coating surface density of the positive electrode is m1 The coating surface density of the negative electrode is m2 Satisfy between: Among them, N is the ratio of the positive electrode capacity to the negative electrode capacity per unit area, A is the gram capacity of the positive electrode active material, B is the gram capacity of the negative electrode active material, w1 is the mass ratio of the positive electrode active material at the positive electrode, and w2 is the mass ratio of the negative electrode active material at the negative electrode.

[0043] In this embodiment, the positive electrode capacity per unit area can be obtained by multiplying the coating surface density of the positive electrode, the mass ratio of the positive electrode active material, and the gram capacity of the positive electrode active material, and the negative electrode capacity per unit area can be obtained by multiplying the coating surface density of the negative electrode, the mass ratio of the negative electrode active material, and the gram capacity of the negative electrode active material. Wherein, N can be a constant that satisfies 0 <N<1。

[0044] In some embodiments, a porous layer 120 is provided on one side of the base film 110, and the coating surface density of the positive electrode is m1 Satisfy: ρ m1 ≤230g / m 2 .

[0045] In this embodiment, the porous layer 120 is arranged on one side of the base film 110. The positive electrode and the negative electrode on both sides of the base film 110 are thick electrodes. The porous layer 120 can be located on the side of the base film 110 close to the negative electrode to ensure the wettability of the thick electrode.

[0046] It should be noted that when the coating surface density of the positive electrode is less than 230 g / m 2 When the porous layer 120 is disposed on the side of the base film 110 close to the positive electrode, the effect of ensuring the wettability of the thick electrode can also be achieved.

[0047] In some embodiments, porous layers 120 are provided on both sides of the base film 110, and the coating surface density of the positive electrode is m1 Meet: 230g / m 2 ≤ρ m1 ≤320g / m 2 .

[0048] In this embodiment, when the coating surface density of the positive electrode is m1 Meet 230g / m 2≤ρ m1 ≤320g / m 2 When the porous layer 120 is provided on both sides of the base film 110, the wettability of the thick electrode can be improved, thereby improving the electrical performance of the battery.

[0049] It should be noted that the thick electrode mentioned in the present application can be formed by coating both sides of the battery electrode.

[0050] In some embodiments, the porous layer 120 on both sides of the base film 110 is provided with thick electrodes.

[0051] In this embodiment, porous layers 120 are provided on both sides of the base membrane 110, and thick electrodes are provided on the side away from the base membrane 110 of the porous layers 120 on both sides, that is, the positive electrode and the negative electrode on both sides of the battery separator are thick electrodes, which can improve the wettability of the thick electrode and increase the energy density of the battery, thereby improving the electrical performance of the battery.

[0052] It should be noted that when the coating surface density of the positive electrode is m1 More than 320g / m 2 When the porous layer 120 is merely provided on both sides of the base film 110, the technical problem of poor electrolyte infiltration in the thick electrode technology cannot be solved.

[0053] Specifically, when the coating surface density of the positive electrode is m1 Satisfy ρ m1 ≤230g / m 2 When the coating surface density of the positive electrode is ρ m1 Meet 230g / m 2 ≤ρ m1 ≤320g / m 2 When the porous layer 120 is provided on both sides of the base film 110 .

[0054] In some embodiments, the porous layer 120 includes one or more of a porous layer of nano-aluminum oxide material, a porous layer of boehmite material, a porous layer of polyvinylidene fluoride material, a porous layer of polytetrafluoroethylene material, a porous layer of polyimide material, a porous layer of polyacrylic acid material, a porous layer of polyethylene material, and a porous layer of polypropylene material.

[0055] In this embodiment, the material of the porous layer 120 can be one or more of nano-aluminum oxide, boehmite, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyacrylic acid, polyethylene, polypropylene, etc., and thus a porous layer 120 with a sponge structure can be formed, thereby ensuring the affinity between the porous layer 120 and the electrolyte, and providing an exclusive channel for the electrolyte between the battery separator and the thick electrode to increase the liquid retention performance of the battery separator, thereby improving the wettability of the thick electrode, improving the transmission performance of ions and electrons, avoiding the decrease in the conductivity of electrons and ions, and avoiding the decrease in the electrical performance of the battery.

[0056] In some embodiments, the present application also provides a large-capacity battery, which includes thick electrodes and a battery separator provided in the present application, the thick electrodes are respectively arranged on both sides of the battery separator, and an electrolyte is provided between the thick electrodes and the battery separator.

[0057] In this embodiment, the large-capacity battery can be a thick electrode battery, and the thick electrodes are respectively arranged on both sides of the battery separator, and an electrolyte is arranged between the thick electrode and the battery separator, and the electrolyte can be composed of a solvent, a lithium salt and an additive. The electrolyte plays the role of transmitting lithium ions in the battery, ensuring that the battery can efficiently store and release energy. Lithium battery electrolytes usually use high-purity organic solvents, which have good solubility and ion conductivity, and can effectively support the transmission of lithium ions. Organic solvents include carbonate compounds, such as ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC).

[0058] Lithium salt is one of the key components in the electrolyte. Commonly used lithium salts include lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4) and lithium tetrafluoroborate (LiBF4). Among them, lithium hexafluorophosphate (LiPF6) is the most commonly used lithium salt. It is an irreplaceable electrolyte salt in lithium-ion batteries because of its high conductivity, electrochemical stability and low internal resistance.

[0059] In order to improve the performance of the electrolyte, some functional additives are usually added, such as film-forming additives (such as vinylene carbonate, VC), flame retardant additives, etc. Additives can improve the electrochemical stability of the electrolyte, improve the safety and cycle life of the battery.

[0060] The beneficial effects of the present application are further illustrated below in conjunction with the embodiments.

[0061] Comparative Example 1:

[0062] The battery cell 1 can be composed of a positive electrode, a negative electrode, an electrolyte and a battery separator. The battery separator adopts a base film 110 + a common glue-coated separator without other special structures. It is based on thick electrode technology (the coating surface density of the positive electrode is 300g / m 2), and the nominal capacity of cell 1 is 350 ampere hours.

[0063] Embodiment 1:

[0064] The battery cell 2 may be composed of a positive electrode, a negative electrode, an electrolyte and a battery separator. The battery separator adopts a "sponge-like" porous layer 120 separator. The porous layer 120 may be composed of boehmite and an aqueous glue. The "sponge-like" porous layer 120 is located on both sides of the base film 110. The thick electrode technology (coating surface density of the positive electrode is 300g / m 2 ), the nominal capacity of cell 2 is 350 ampere hours.

[0065] Test Example 1:

[0066] The positive and negative electrodes, electrolytes and total thickness of the separators of cell 1 and cell 2 are the same. The interface of the fully charged cell 1 can be referred to as Figure 3 and Figure 4 , Figure 3 This is a diagram of the interface of the fully charged negative electrode sheet of the battery cell 1 without the porous layer 120. Figure 4 It is a diagram of the interface of the negative electrode sheet of the battery cell 2 provided with the porous layer 120 after being fully charged.

[0067] from Figure 3 and Figure 4 It can be seen that due to poor electrolyte infiltration, black spots appear in the middle of the fully charged negative electrode interface of cell 1 after formation, while the fully charged negative electrode interface of cell 2 is good after formation.

[0068] Test Example 2:

[0069] Table 1

[0070] Serial number Number of cycles Expansion force(kgf) Capacity retention rate Battery 1 1000 1800 89.3％ Battery 2 1000 430 92.5％

[0071] Cell 1 and cell 2 are charged and discharged for 1000 cycles respectively. Figure 5 As shown in Table 1, after 1000 cycles of charge and discharge, the expansion force of battery cell 1 is 1800kgf, and the cycle capacity retention rate is 89.3%; after 1000 cycles of charge and discharge using the "sponge-like" porous layer 120 separator, the expansion force of battery cell 2 is 430kgf, and the cycle capacity retention rate is 92.5%.

[0072] At the same time, the capacity of battery cell 1 and battery cell 2 is 350 ampere-hours. Under full operating conditions during the entire life cycle, the expansion force of battery cell 1 is ≤6500kgf, and under full operating conditions during the entire life cycle, the expansion force of battery cell 2 is ≤3500kgf. Therefore, it can be fully proved that the "sponge-like" porous layer 120 diaphragm can effectively improve the performance of batteries with thick electrodes and can provide a certain buffering effect on the expansion force during the cycle process.

[0073] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A battery separator, characterized in that: The invention comprises a base film and a porous layer arranged on one side or both sides of the base film, wherein a thick electrode is arranged on a side of the porous layer away from the base film.

2. The battery separator according to claim 1, characterized in that: The thickness between the porous layer and the base film satisfies: b=xa; wherein 0≤x≤1, a is the thickness of the porous layer, and b is the thickness of the base film.

3. The battery separator according to claim 2, characterized in that: x satisfies: 0.2≤x≤0.

5.

4. The battery separator according to claim 1, characterized in that: The pore size of the porous layer is larger than the pore size of the base film.

5. The battery separator according to claim 1, characterized in that: The positive electrode and the negative electrode on both sides of the base film are the thick electrodes, and the coating surface density of the positive electrode is m1 The coating surface density of the negative electrode is m2 Satisfy between: Among them, N is the ratio of the positive electrode capacity to the negative electrode capacity per unit area, A is the gram capacity of the positive electrode active material, B is the gram capacity of the negative electrode active material, w1 is the mass ratio of the positive electrode active material at the positive electrode, and w2 is the mass ratio of the negative electrode active material at the negative electrode.

6. The battery separator according to claim 5, characterized in that: The porous layer is provided on one side of the base film, and the coating surface density of the positive electrode is m1 Satisfy: ρ m1 ≤230g / m 2 .

7. The battery separator according to claim 5, characterized in that The porous layer is provided on both sides of the base film, and the coating surface density of the positive electrode is m1 Meet: 230g / m 2 ≤ρ m1 ≤320g / m 2 .

8. The battery separator according to claim 5, characterized in that: N satisfies: 0 <N<1。 9. The battery separator according to any one of claims 1 to 8, characterized in that An electrolyte is provided between the battery separator and the thick electrode; or / and, The porous layer includes one or more of a porous layer made of nano-aluminum oxide, a porous layer made of boehmite, a porous layer made of polyvinylidene fluoride, a porous layer made of polytetrafluoroethylene, a porous layer made of polyimide, a porous layer made of polyacrylic acid, a porous layer made of polyethylene, and a porous layer made of polypropylene.

10. A large capacity battery, characterized in that: It comprises a thick electrode and a battery separator according to any one of claims 1 to 9, wherein the thick electrodes are respectively arranged on both sides of the battery separator, and an electrolyte is arranged between the thick electrode and the battery separator.

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