Battery diaphragm as well as preparation method and application thereof

Abstract

The invention discloses a battery diaphragm as well as a preparation method and application thereof, and belongs to the technical field of energy storage. The battery diaphragm comprises a base membrane and a modification layer which are laminated, the modification layer comprises a solid electrolyte and a binder; the modification layer is also modified with an oxygen-containing functional group and / or a nitrogen-containing functional group; the modification layer has a gradient pore structure of which the pore diameter is gradually reduced from a bonding interface of the modification layer and the base membrane to the surface of the modification layer. The oxygen-containing functional group and / or the nitrogen-containing functional group are / is introduced into the modification layer, the oxygen-containing functional group and / or the nitrogen-containing functional group and solvent molecules in an electrolyte can form a stable structure, electrolyte volatilization is inhibited, and the good infiltration performance between the diaphragm and the electrolyte can be achieved; and the gradient pore structure of the modification layer is beneficial to optimization of an ion transmission path, formation of capillary action, promotion of uniform distribution of the electrolyte and reduction of local evaporation. The battery diaphragm disclosed by the invention is beneficial to preparation of batteries with good performance, especially lithium ion batteries.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of energy storage, and particularly relates to a battery separator, a preparation method and application thereof. BACKGROUND

[0002] Traditional lithium ion battery separators are mostly polyolefin porous membranes (such as polyethylene PE, polypropylene PP, etc.), but their surface is inert, leading to poor adhesion with electrodes and high interface impedance. In the prior art, lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP), lithium lanthanum zirconium oxide (LLZO) and the like are often used as fast ion conductors to improve lithium ion transmission, but their interface compatibility with polyolefin-based membranes is poor, direct coating is easy to block pores, and electrolyte diffusion is limited. Uneven electrolyte infiltration can easily cause local polarization and exacerbate lithium dendrite growth, especially at the corners of the battery, which is prone to lithium precipitation, and there is a safety hazard. SUMMARY

[0003] In order to overcome at least one of the problems existing in the prior art, one of the purposes of the present application is to provide a battery separator, which has high adhesion strength with electrodes, optimized lithium ion transmission path and effectively inhibited lithium precipitation phenomenon through interface modification and gradient pore structure design.

[0004] The second purpose of the present application is to provide a preparation method of the above-mentioned battery separator.

[0005] The third purpose of the present application is to provide a battery.

[0006] In order to achieve the above-mentioned purposes, the technical solution adopted by the present application is: The first aspect of the present application provides a battery separator, comprising a base film and a modification layer arranged in layers; the modification layer comprises a solid-state electrolyte and a binder; the modification layer is further modified with oxygen-containing functional groups and / or nitrogen-containing functional groups; the modification layer has a gradient pore structure, and the gradient pore structure is that the pore size gradually decreases along the interface between the modification layer and the base film to the surface of the modification layer.

[0007] Preferably, the pore size of the interface between the modification layer and the base film is 100-300 nm; for example, it can be any value or a range value between any two values selected from 100 nm, 150 nm, 200 nm, 250 nm or 300 nm.

[0008] Preferably, the pore size of the surface of the modification layer is 10-50 nm; for example, it can be any value or a range value between any two values selected from 10 nm, 20 nm, 30 nm, 40 nm or 50 nm.

[0009] Preferably, the pore size (D max ) of the interface between the modification layer and the base film is smaller than the pore size (D minThe ratio of (D) max / D min The value is 4 to 30; for example, it can be any value or a range between any two of 4, 5, 6, 7, 8, 10, 15, 20, 25 or 30; more preferably, it is 5 to 15.

[0010] Preferably, the pore size (D) at the interface between the modified layer and the base film is... max ) and the pore size (D) of the surface of the modified layer min The difference (D) max -D min The wavelength range is 70~290nm; for example, it can be any value or a range between any two of 70nm, 80nm, 100nm, 150nm, 180nm, 200nm, 220nm, 250nm, 280nm or 290nm; more preferably, it is 100~250nm.

[0011] The gradient pore structure of this invention can guide the uniform and orderly transport of lithium ions, effectively suppressing dendrite growth. The aforementioned limitation of the pore size ratio or pore size difference is beneficial for improving the ion transport gradient; if the ratio or difference is too small, the gradient effect is not obvious, and the optimization of the ion transport path is minimal; if the ratio or difference is too large, it may lead to a decrease in the mechanical strength of the dense surface layer or an increase in the difficulty of the fabrication process. Furthermore, the combined limitation of the aforementioned pore size ratio or pore size difference is beneficial for more effectively improving the ion transport gradient.

[0012] Preferably, the thickness of the modification layer is 1~5μm; for example, it can be any value of 1μm, 2μm, 3μm, 4μm or 5μm or a range between any two.

[0013] Preferably, the oxygen content in the modified layer is 5-15% by mass; for example, it can be any value of 5%, 8%, 10%, 12% or 15% or a range between any two.

[0014] Preferably, the nitrogen content in the modified layer is 1-5% by mass; for example, it can be any value of 1%, 2%, 3%, 4% or 5% or a range between any two.

[0015] By introducing oxygen- and nitrogen-containing functional groups, a stable structure can be formed with solvent molecules in the electrolyte, inhibiting electrolyte volatilization. Simultaneously, the ion transport pathway is optimized, promoting uniform electrolyte distribution and reducing localized evaporation. Furthermore, the synergistic effect between oxygen and nitrogen content and pore size gradient can further improve the membrane's capacity retention.

[0016] Preferably, the mass ratio of oxygen element to nitrogen element (O / N) in the modification layer is (0.75-15):1; for example, it can be any one of 0.75:1, 1:1, 2:1, 3:1, 5:1, 8:1, 10:1, 12:1 or 15:1 or a range value between any two of them; further preferably, it is (1-10):1.

[0017] Controlling the suitable mass ratio of oxygen element to nitrogen element is conducive to the synergistic effect of oxygen-containing and nitrogen-containing functional groups, and the formation of more stable and more diverse hydrogen bonds or coordination bond interactions with various solvent molecules (such as EC, DEC, etc.) in the electrolyte, thereby more effectively inhibiting the volatilization of the electrolyte, achieving more excellent wetting performance, higher bonding strength and better interface stability.

[0018] Preferably, the oxygen-containing functional group includes a hydroxyl group, a carboxyl group or a combination thereof; further preferably, the oxygen-containing functional group includes a hydroxyl group and a carboxyl group.

[0019] Preferably, the nitrogen-containing functional group includes an amino group.

[0020] Preferably, the mass ratio of the solid-state electrolyte to the binder is (3-15):1; further preferably, it is (4-12):1; and more further preferably, it is (5-10):1.

[0021] Controlling the suitable mass ratio of the solid-state electrolyte to the binder ensures the uniformity and mechanical strength of the modification layer.

[0022] Preferably, the solid-state electrolyte includes at least one of lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP) or lithium lanthanum zirconium oxide (LLZO).

[0023] Preferably, the binder includes at least one of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyethylene oxide (PEO), sodium alginate (Alginate), polytetrafluoroethylene (PTFE), polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN) or polyvinyl alcohol (PVA); further preferably, the binder includes at least one of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polyethylene oxide (PEO) or polytetrafluoroethylene (PTFE); and more further preferably, the binder includes polyvinylidene fluoride (PVDF), polyacrylic acid (PAA) or a combination thereof.

[0024] In some embodiments of the present application, the pore size of the base film is uniformly distributed.

[0025] Preferably, the pore size of the base film is 0.1-1 μm; for example, it can be any one of 0.1 μm, 0.3 μm, 0.5 μm, 0.8 μm or 1 μm or a range value between any two of them.

[0026] Preferably, the material of the base film is selected from polyolefins; further preferably, the polyolefins include polyethylene (PE), polypropylene (PP) or a combination thereof.

[0027] Preferably, the battery separator is a solid-state electrolyte battery separator.

[0028] The second aspect of the present application provides a method for preparing a battery separator, comprising the following steps: dispersing a solid-state electrolyte and a binder in a solvent to form a slurry; introducing an active functional group into the slurry to form a modified slurry, the active functional group including an oxygen-containing functional group, a nitrogen-containing functional group or a combination thereof; applying the modified slurry to the surface of a base film, drying, and roll forming to obtain a battery separator as described in the first aspect of the present application.

[0029] Preferably, the introduction of the active functional group includes plasma treatment, chemical grafting treatment or a combination thereof.

[0030] Preferably, the plasma treatment specifically includes the following steps: plasma treating the slurry to form a modified slurry.

[0031] Preferably, the treatment gas of the plasma treatment includes oxygen, nitrogen or a combination thereof; further preferably, the treatment gas of the plasma treatment includes oxygen and nitrogen; the volume ratio of oxygen and nitrogen can be 1: (0.5-2), for example, 1:0.5, 1:1, 1:1.5, 1:2, etc.

[0032] Preferably, the treatment power of the plasma treatment is 100-200 W; for example, it can be any one of 100 W, 120 W, 150 W, 180 W or 200 W or a range value between any two of them.

[0033] Preferably, the treatment time of the plasma treatment is 1-10 min; for example, it can be any one of 1 min, 3 min, 5 min, 7 min or 10 min or a range value between any two of them.

[0034] Preferably, the treatment reagent of the chemical grafting treatment includes a coupling agent.

[0035] Preferably, the chemical grafting treatment specifically includes the following steps: mixing the slurry with a coupling agent for chemical grafting treatment to form a modified slurry.

[0036] Preferably, the coupling agent comprises an amino coupling agent; further preferably, the amino coupling agent comprises 3-aminopropyltrimethoxysilane (APTMS), 3-aminopropyltriethoxysilane (APTES), or a combination thereof; still further preferably, the amino coupling agent is selected from 3-aminopropyltriethoxysilane (APTES).

[0037] Preferably, the treatment temperature of the chemical grafting treatment is 50-70℃; for example, it can be any one of 50℃, 55℃, 60℃, 65℃, or 70℃, or a range value between any two of them.

[0038] Preferably, the treatment time of the chemical grafting treatment is 1-3h; for example, it can be any one of 1h, 2h, or 3h, or a range value between any two of them.

[0039] Preferably, the solvent comprises an organic solvent, water, or a combination thereof; further preferably, the organic solvent comprises at least one of N-methylpyrrolidone (NMP), acetone, toluene, isopropyl alcohol, or ethyl acetate.

[0040] Preferably, the way of applying the modified slurry to the surface of the base film is selected from coating; further preferably, the speed of the coating is 0.1-1m / min; for example, it can be any one of 0.1m / min, 0.3m / min, 0.5m / min, 0.7m / min, or 1m / min, or a range value between any two of them.

[0041] Preferably, the temperature of the drying is 50-100℃; for example, it can be any one of 50℃, 60℃, 70℃, 80℃, 90℃, or 100℃, or a range value between any two of them.

[0042] The third aspect of the present application provides a battery comprising the battery separator according to the first aspect of the present application.

[0043] Preferably, the battery further comprises an electrolyte; the solvent of the electrolyte comprises at least one of ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or propylene carbonate (PC); further preferably, the solvent of the electrolyte comprises ethylene carbonate (EC), diethyl carbonate (DEC), or a combination thereof.

[0044] The battery separator provided by the present application can form stable combination with the solvent molecules (such as EC, DEC, etc.) in the electrolyte, thereby inhibiting the evaporation of the electrolyte and achieving good wettability, and the obtained battery has lower interface impedance and higher capacity retention rate.

[0045] Preferably, the battery is a solid electrolyte battery.

[0046] Preferably, the battery is a lithium ion battery.

[0047] The gradient pore structure of the modification layer in the battery separator of the present application is beneficial to optimizing the transmission path of lithium ions, inhibiting lithium precipitation, and obtaining a lithium ion battery with good safety performance.

[0048] The beneficial effects of the present application are: the present application introduces oxygen-containing functional groups and / or nitrogen-containing functional groups into the modification layer, which can form a stable structure with solvent molecules in the electrolyte, inhibit electrolyte evaporation, and also achieve good wettability between the separator and the electrolyte; the gradient pore structure of the modification layer is beneficial to optimizing the ion transmission path and also beneficial to forming capillary action, promoting uniform distribution of the electrolyte and reducing local evaporation; further, the gradient pore structure and the functional groups can play a synergistic role to jointly optimize the wettability of the electrolyte, significantly reduce the evaporation rate of the electrolyte, reduce the interfacial impedance, reduce the capacity decay caused by electrolyte loss, and improve the adhesion strength of the separator and the electrode. The battery separator provided by the present application is beneficial to preparing a battery with good electrical performance, especially a lithium ion battery. The battery separator of the present application is beneficial to preparing a battery with good performance, especially a lithium ion battery. DETAILED DESCRIPTION

[0049] The content of the present application will be further described in detail through specific examples. It should also be understood that the following examples are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Some non-essential improvements and adjustments made by those skilled in the art based on the principles described in the present application are within the scope of protection of the present application. The following examples of specific process parameters are only one example in the appropriate range, i.e. those skilled in the art can make appropriate choices within the scope of the present application, and are not limited to the specific data of the following examples. The raw materials, reagents or devices used in the following examples and comparative examples are commercially available or can be obtained by known methods unless otherwise specified.

[0050] In the following examples and comparative examples, the chemical formula of lithium aluminum titanium phosphate (LATP) is Li 1.3 Al 0.3 Ti 1.7 (PO4)3; the chemical formula of lithium aluminum germanium phosphate (LAGP) is Li 1.5 Al 0.5 Ge 1.5 (PO4)3.

[0051] Example 1 A battery separator, the preparation steps are as follows: 1) Slurry preparation: LATP powder (particle size 200 nm) and polyvinylidene fluoride (PVDF) binder with a mass ratio of 8:1 were dispersed in NMP solvent, stirred for 1.5 hours to form a uniform slurry.

[0052] 2) Plasma treatment: The slurry was treated by plasma, the treatment gas was O2 / N2 mixed gas (volume ratio 1:1), the treatment power was 150 W, and the treatment time was 5 minutes, so as to introduce oxygen (-OH, -COOH) functional groups and form a modified slurry.

[0053] 3) Coating and roll forming: The modified slurry was coated on the surface of the PE base film (pore size 200 nm) at a coating speed of 0.5 m / min, dried at 80°C; then roll forming was carried out to form a modification layer; the thickness of the modification layer was 2 μm, the modification layer had a gradient distribution of pore size structure, the pore size gradually decreased from the interface of the modification layer and the base film to the surface of the modification layer, the pore size D max at the interface of the modification layer and the base film was 200 nm, the pore size D min at the surface of the modification layer was 30 nm, the pore size ratio D max / D min was 6.67; the O / N mass ratio of the modification layer was 5:1. The specific gradient pore structure was realized by controlling the coating speed, drying temperature and time, roll pressure and layered design.

[0054] Example 2 A battery separator, the preparation steps are as follows: 1) Slurry preparation: LATP powder (particle size 300 nm) and polyacrylic acid (PAA) binder with a mass ratio of 6:1 were dispersed in deionized water, stirred for 1.5 hours to form a uniform slurry.

[0055] 2) Chemical grafting treatment: 3-aminopropyltriethoxysilane (APTES) was added as a coupling agent in the slurry to react, the reaction temperature was 60°C, and the reaction time was 2 hours, so as to introduce amino (-NH2) functional groups and form a modified slurry.

[0056] 3) Coating and roll forming: The modified slurry was coated on the surface of the PP base film (pore size 150 nm) at a coating speed of 0.3 m / min, dried at 70°C; then roll forming was carried out to form a modification layer; the thickness of the modification layer was 3 μm, the modification layer had a gradient distribution of pore size structure, the pore size gradually decreased from the interface of the modification layer and the base film to the surface of the modification layer, the pore size D max at the interface of the modification layer and the base film was 150 nm, the pore size D min at the surface of the modification layer was 20 nm, the pore size ratio D max / D minThe O / N mass ratio of the modification layer is 0.75:1. The specific gradient pore structure is realized by controlling the coating speed, drying temperature and time, rolling pressure and layered design.

[0057] Example 3 A battery separator, the preparation steps are as follows: 1) Slurry preparation: take the LATP powder (particle size 200 nm) and polyethylene oxide (PEO) binder with a mass ratio of 10:1, disperse in NMP solvent, stir for 1.5 hours to form a uniform slurry.

[0058] 2) Plasma treatment: the slurry is treated by plasma, the treatment gas is O2, the treatment power is 200 W, and the treatment time is 10 minutes, so as to introduce oxygen (-OH, -COOH) functional groups and form a modified slurry.

[0059] 3) Coating and rolling forming: the modified slurry is coated on the surface of the PP base film (pore size 200 nm) at a coating speed of 0.3 m / min, dried at 70°C; then rolling forming is carried out to form a modification layer; the thickness of the modification layer is 3 μm, the modification layer has a gradient distribution of pore size, the pore size gradually decreases from the interface between the modification layer and the base film to the surface of the modification layer, the pore size D max of the interface between the modification layer and the base film is 280 nm, the pore size D min of the surface of the modification layer is 20 nm, and the pore size ratio D max / D min is 14; the O / N mass ratio of the modification layer is 15:1. The specific gradient pore structure is realized by controlling the coating speed, drying temperature and time, rolling pressure and layered design.

[0060] Example 4 A battery separator, which is different from example 1 in that the solid content of the slurry and the rolling process parameters are adjusted, so that the pore size D max of the interface between the modification layer and the base film is 300 nm, the pore size D min of the surface of the modification layer is 10 nm, and the pore size ratio D max / D min is 30; other raw materials and preparation conditions are the same as example 1.

[0061] Example 5 A battery separator, which is different from example 1 in that the solid content of the slurry and the rolling process parameters are adjusted, so that the pore size D max of the interface between the modification layer and the base film is 120 nm, the pore size D min of the surface of the modification layer is 30 nm, and the pore size ratio D max / D min is 4; other raw materials and preparation conditions are the same as example 1.

[0062] Example 6 A battery separator, which is different from Example 1 in that the LATP powder in this example is replaced by an equal amount of LAGP powder; other raw materials and preparation conditions are the same as those in Example 1.

[0063] Comparative Example 1 A battery separator (without functional group modification, with gradient pore structure), which is different from Example 1 in that step 2) is omitted in this example; the slurry formed in step 1) is directly used for coating and roll forming in step 3), and the modification layer has a gradient distribution of pore size structure, which is the same as that in Example 1; other raw materials and preparation conditions are the same as those in Example 1.

[0064] Comparative Example 2 A battery separator (without functional group modification, without gradient pore structure), which is different from Example 1 in that step 2) is omitted in this example; the slurry formed in step 1) is directly used for coating and roll forming in step 3), and the roll forming process in step 3) is adjusted, and the modification layer has a uniform distribution of pore size structure, with a pore size of 50 nm; other raw materials and preparation conditions are the same as those in Example 1.

[0065] Comparative Example 3 A battery separator (with functional group modification, without gradient pore structure), the preparation steps are as follows: 1) Slurry preparation: LATP powder (particle size 200 nm) and polyvinylidene fluoride (PVDF) binder with a mass ratio of 8:1 are dispersed in NMP solvent, and stirred for 1.5 hours to form a uniform slurry.

[0066] 2) Plasma treatment: the slurry is subjected to plasma treatment, the treatment gas is O2 / N2 mixed gas (volume ratio 1:1), the treatment power is 150 W, and the treatment time is 5 minutes, so as to introduce oxygen-containing (-OH, -COOH) functional groups and form a modified slurry.

[0067] 3) Coating and roll forming: the modified slurry is coated on the surface of the PE-based film (pore size 200 nm) at a coating speed of 0.5 m / min, and dried at 80°C; then roll forming is carried out to form a modification layer; the thickness of the modification layer is 2 μm, and the modification layer has a uniform distribution of pore size structure by roll forming process in this example, and the pore size of the modification layer is 50 nm.

[0068] The comparison of the schemes of Examples 1-5 and Comparative Examples 1-3 is shown in Table 1.

[0069] Table 1 Comparison of schemes of Examples 1-5 and Comparative Examples 1-3

[0070] Performance test 1) Adhesion strength: peel test was performed on the separators of examples and comparative examples according to ASTM D903-98 (2025) standard.

[0071] 2) Immersion time: electrolyte was added dropwise to the surface of the separators of examples and comparative examples, and the complete immersion time was recorded.

[0072] 3) Lithium precipitation inhibition rate: the separators of examples and comparative examples were assembled into batteries, and after the battery working cycle, the battery was disassembled, and the area ratio of lithium precipitation in the corner of the battery was observed by scanning electron microscope (SEM).

[0073] 4) Cycle capacity retention rate: the separators of examples and comparative examples were assembled into batteries, and the cycle capacity retention rate of the batteries was tested at 0.5C.

[0074] 5) Electrolyte retention rate: the separators of examples and comparative examples were assembled into batteries, and the full charge battery after charging was stored at 60°C high temperature environment for 30 days, and the electrolyte mass loss and electrolyte retention rate were calculated by weighing method.

[0075] 6) Comprehensive performance index P: a comprehensive index for quantifying the adhesion performance and ion transmission efficiency of the separator, which needs to meet P≥8.0. The calculation formula of comprehensive performance index P is as follows:

[0076] Wherein, k1=0.8, k2=0.5; α, β are weight coefficients, α=0.6, β=0.4; D max and D min are the maximum pore size and the minimum pore size of the separator modification layer respectively; [O%] and [N%] are the mass content of oxygen element and the mass content of nitrogen element in the separator modification layer respectively. The effective threshold value is P≥8.0, when P≥8.0, the adhesion strength, immersion speed and lithium precipitation inhibition capacity of the separator reach the state of synergistic optimization, which meets the demand of high performance battery.

[0077] In examples 1~6, [O%] is 5%~15%, [N%] is 1%~5%.

[0078] The performance test results are shown in Table 2.

[0079] Table 2 Performance test results of the separators of examples 1~6 and comparative examples 1~3

[0080] As can be seen from Table 2, the battery separator of the present application examples 1-6 is modified by functional groups and cooperates with the gradient pore structure, the comprehensive performance index P is significantly higher than that of the scheme in the comparative example (P of examples 1-6 is greater than or equal to 8.7, P of comparative examples 1-3 is less than or equal to 7.5), the bonding strength is greater than or equal to 14 N / m, the infiltration time is less than or equal to 130 s, the corner lithium precipitation inhibition rate is greater than or equal to 92%, the capacity retention rate after 500 cycles is greater than or equal to 91%, and the electrolyte retention rate is increased to more than 90%, effectively solving the problems of poor adhesion, high risk of lithium precipitation, cycle performance decay and electrolyte evaporation of the existing lithium ion battery separator.

[0081] In the comparative example 1, the functional group modification is not used, the bonding force between the modification layer and the base film is weak, the bonding strength of the battery separator is only 6.5 N / m, the interface adhesion between the modification layer and the base film is insufficient, and the adhesion performance of the battery separator cannot be met; and the comparative example 1 cannot play the synergistic effect of the specific oxygen and nitrogen element content and the pore size gradient, the cycle capacity retention rate is low, only 78.4%; at the same time, the gradient pore structure is not combined with the functional group modification, resulting in fast electrolyte evaporation rate, low electrolyte retention rate after cycling (72.3%), long infiltration time (300 s) and low lithium precipitation inhibition rate (70%).

[0082] In the comparative example 2, the gradient pore structure is not set but a uniform pore size structure is used, which blocks the diffusion of electrolyte, prolongs the infiltration time to 180 s, and also has poor effect on inhibiting lithium precipitation, with lithium precipitation inhibition rate of only 80%; the gradient pore structure is not combined with the functional group modification, resulting in low cycle capacity retention rate (83.0%) and low electrolyte retention rate after cycling (78.0%).

[0083] In the comparative example 3, the functional group modification is used but the gradient pore structure is not set, the cycle capacity retention rate (89.0%) and the electrolyte retention rate (76.8%) are poor, and it is difficult to meet the use requirements of the battery separator.

[0084] In summary, the present application introduces oxygen-containing functional groups and / or nitrogen-containing functional groups into the modification layer, which can form a stable structure with the solvent molecules in the electrolyte, inhibit the evaporation of the electrolyte, and also achieve good infiltration performance between the separator and the electrolyte; the gradient pore structure of the modification layer is beneficial to optimizing the ion transmission path and also beneficial to forming capillary action, promoting the uniform distribution of the electrolyte and reducing local evaporation; further, the gradient pore structure and the functional groups can play a synergistic effect, together optimize the infiltration path of the electrolyte, significantly reduce the evaporation rate of the electrolyte, reduce the interface impedance, reduce the capacity decay caused by the loss of electrolyte, and improve the adhesion strength of the separator and the electrode. The battery separator of the present application is beneficial to preparing a battery with good performance, especially a lithium ion battery.

Claims

1. A battery separator, characterized by, The battery separator comprises a base film and a modification layer stacked together; the modification layer comprises a solid-state electrolyte and a binder; the modification layer is further modified with oxygen-containing functional groups and / or nitrogen-containing functional groups; the modification layer has a gradient pore structure with a pore size gradually decreasing from the interface between the modification layer and the base film to the surface of the modification layer.

2. The battery separator of claim 1, wherein, The pore size at the interface between the modification layer and the base film is 100-300 nm; and / or, the pore size at the surface of the modification layer is 10-50 nm; and / or, the ratio of the pore size at the interface between the modification layer and the base film to the pore size at the surface of the modification layer is 4-30; and / or, the difference between the pore size at the interface between the modification layer and the base film and the pore size at the surface of the modification layer is 70-290 nm; and / or, the thickness of the modification layer is 1-5 μm.

3. The battery separator of claim 1, wherein, The mass content of oxygen in the modification layer is 5-15%; and / or, the mass content of nitrogen in the modification layer is 1-5%; and / or, the mass ratio of oxygen to nitrogen in the modification layer is (0.75-15):

1.

4. The battery separator of claim 1, wherein, The oxygen-containing functional groups include hydroxyl groups, carboxyl groups, or a combination thereof; and / or, the nitrogen-containing functional groups include amino groups.

5. The battery separator of claim 1, wherein, The mass ratio of the solid-state electrolyte to the binder is (5-10):1; and / or, the solid-state electrolyte comprises at least one of lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, or lithium lanthanum zirconium oxide; and / or, the binder comprises at least one of polyvinylidene fluoride, polyacrylic acid, butadiene-styrene rubber, carboxymethyl cellulose, polyethylene oxide, sodium alginate, polytetrafluoroethylene, polyvinylpyrrolidone, polyacrylonitrile, or polyvinyl alcohol.

6. The battery separator of claim 1, wherein, The pore size of the base film is 0.1-1 μm; and / or, the material of the base film is selected from polyolefins.

7. A method of producing a battery separator, characterized by, The method comprises the following steps: dispersing a solid-state electrolyte and a binder in a solvent to form a slurry; introducing active functional groups into the slurry to form a modified slurry, the active functional groups including oxygen-containing functional groups, nitrogen-containing functional groups, or a combination thereof; applying the modified slurry to the surface of a base film, drying, and roll forming to obtain the battery separator of any one of claims 1-6.

8. The preparation method according to claim 7, characterized in that, The active functional groups are introduced by plasma treatment, chemical grafting treatment, or a combination thereof.

9. The production method according to claim 8, characterized by, The treatment gas for the plasma treatment comprises oxygen, nitrogen, or a combination thereof; and / or, the treatment power for the plasma treatment is 100-200 W; and / or, the treatment time for the plasma treatment is 1-10 min; and / or, the treatment reagent for the chemical grafting treatment comprises a coupling agent; and / or, the treatment temperature for the chemical grafting treatment is 50-70 °C; and / or, the treatment time for the chemical grafting treatment is 1-3 h.

10. A battery, characterized by The battery comprises the battery separator of any one of claims 1-6.

Images