Battery diaphragm, secondary battery, battery pack and energy storage system

Abstract

The invention provides a battery diaphragm, a secondary battery, a battery pack and an energy storage system, the battery diaphragm comprises a base membrane and a functional layer coating at least one surface of the base membrane, the functional layer comprises ceramic particles, oxygen atoms on the surfaces of the ceramic particles are grafted with ion conductive groups containing M, and M is selected from at least one of B, S, Si, C and N. Compared with ceramic particles, the ionic conductive group can be combined with alkali metal ions in electrolyte more easily, so that the Lewis acid-base action between the ceramic particles and the alkali metal ions in the electrolyte can be inhibited, the ion mobility of the battery diaphragm is improved, and the charge-discharge rate performance of the secondary battery is improved; and the ionic conductive group can improve the wettability of the battery diaphragm and an electrolyte and reduce the polarization phenomenon of the secondary battery, so that the charge-discharge capacity of the secondary battery can be improved, and the performance of the secondary battery is improved.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and in particular, to a battery separator, a secondary battery, a battery pack, and an energy storage system. Background Art

[0002] Secondary batteries generally include: sodium ion batteries, lithium ion batteries, or potassium ion batteries. Taking sodium ion batteries as an example, sodium ion batteries generally include: a positive electrode, a negative electrode, a battery separator, and an electrolyte. The battery separator is disposed between the positive electrode and the negative electrode, and the electrolyte infiltrates the positive electrode, the battery separator, and the negative electrode; when the sodium ion battery is charged, sodium ions are removed from the positive electrode, pass through the battery separator, and are embedded in the negative electrode; when the sodium ion battery is discharged, sodium ions are removed from the negative electrode, pass through the battery separator, and are embedded in the positive electrode. Therefore, the electron insulation of the battery separator affects the isolation effect between the positive electrode and the negative electrode, and the ionic conductivity of the battery separator affects the passing efficiency of sodium ions, thereby affecting the internal resistance, rate charge and discharge, cycle life, and safety of the sodium ion battery. Therefore, the performance of the battery separator affects the performance of the sodium ion battery. Summary of the Invention

[0003] The present application provides a battery separator, a secondary battery, a battery pack, and an energy storage system to improve the performance of the secondary battery.

[0004] In a first aspect, an embodiment of the present application provides a secondary battery, which includes a battery separator. The battery separator includes: a base film, and a functional layer coated on at least one surface of the base film. The functional layer includes ceramic particles, and an ion conductive group containing M is grafted onto the oxygen atoms on the surface of the ceramic particles. M is selected from at least one of B, S, Si, C, and N. Compared with the ceramic particles, the ion conductive group is more likely to combine with alkali metal ions in the electrolyte. Therefore, the Lewis acid-base interaction between the ceramic particles and the alkali metal ions in the electrolyte can be inhibited, and the ionic mobility of the battery separator can be improved, thereby improving the rate charge and discharge performance of the secondary battery; and since the ion conductive group can provide solvation sites, the presence of the ion conductive group can improve the wettability of the battery separator with the electrolyte, so that the alkali metal ions can better contact the surface of the battery separator, and further the amount of alkali metal ions passing through the battery separator can be increased, the polarization phenomenon of the secondary battery can be reduced, and thus the charge and discharge capacity of the secondary battery can be improved, and the performance of the secondary battery can be improved.

[0005] Optionally, in the ion conductive group, M has a negative valence, so that the ion conductive group has a negative charge center. When the battery separator is immersed in the electrolyte, the ion conductive group is more likely to combine with alkali metal ions in the electrolyte, thereby achieving the effects of increasing the wettability of the battery separator with the electrolyte and improving the ionic mobility of the battery separator.

[0006] Further, the ionic conductive group can be selected from any one of the following structures:

[0007]

[0008] Among them, R1 is selected from F or CF3, and R2 and R3 are each independently selected from: C2-C15 saturated hydrocarbons, or C2-C15 unsaturated hydrocarbons. Further, R2 and R3 are each independently selected from: C2-C6 saturated hydrocarbons, or C2-C6 unsaturated hydrocarbons, such as but not limited to: ethyl, vinyl, propyl, isopropyl, propenyl, isopropenyl, butyl, butenyl, pentyl, pentenyl, hexyl, hexenyl, phenyl and other groups, and the groups selected by R2 and R3 can be the same or different, and can be specifically selected according to actual needs, and are not limited herein. A is selected from any one of Li, Na, and K, and * represents the connection site of the ionic conductive group to the oxygen atom. Thus, when the battery separator is immersed in the electrolyte, the ionic conductivity group can dissociate in the electrolyte, making the generated negative charge center more likely to combine with the alkali metal ions in the electrolyte, thereby further achieving the effect of increasing the wettability between the battery separator and the electrolyte and improving the ionic mobility of the battery separator.

[0009] It should be understood that the surface of the ceramic particles has hydroxyl bonds, and the compound containing the ionic conductive group has a leaving group. After the hydrogen in the hydroxyl bond and the leaving group leave, the residue in the compound except the leaving group forms a covalent bond with the oxygen in the hydroxyl bond, thereby realizing the grafting of the ionic conductive group on the surface of the ceramic particles.

[0010] Of course, in addition to being selected from B, S, Si, C, and N, M can also be selected from at least one of the following: other elements in the third main group that can be negatively charged and complex or coordinate with alkali metal ions except B, other elements in the fourth main group that can be negatively charged and complex or coordinate with alkali metal ions except C and Si, other elements in the fifth main group that can be negatively charged and complex or coordinate with alkali metal ions except N, and other elements in the sixth main group that can be negatively charged and complex or coordinate with alkali metal ions except S, and can be specifically selected according to the actual situation, and are not limited herein.

[0011] Optionally, the mass ratio of the ion-conductive group to the ceramic particles can be from 0.005 to 0.1, and further can be set to 0.04 - 0.1, such as but not limited to: 0.04, 0.06, 0.08, 0.1 and other values. In this way, the proportion of ceramic particles is relatively large and the proportion of ion-conductive groups is relatively small, which can avoid reducing the thermal stability and safety of the battery separator when the proportion of ceramic particles is small, and can also avoid increasing the grafting difficulty and grafting effect when the proportion of ion-conductive groups is large. Therefore, limiting the mass ratio of the ion-conductive group to the ceramic particles within a suitable range can not only make the battery separator have good thermal stability and safety, but also improve the wettability and ion mobility of the battery separator, as well as reduce the grafting difficulty and improve the grafting effect, thereby improving the performance of the secondary battery.

[0012] Optionally, the number of ion-conductive groups grafted on the surface of each ceramic particle can be from 1 to 8, such as but not limited to: 1, 2, 3, 4, 5, 6, 7, 8 and other values. In this way, a certain number of ion-conductive groups can be grafted on the surface of each ceramic particle, and it can also avoid the complexity of the grafting process when the number of grafted ion-conductive groups is large, thereby avoiding the increase in manufacturing cost, and avoiding the difficulty of achieving the purpose of improving the wettability and ion mobility of the battery separator when the number of grafted ion-conductive groups is small.

[0013] Among them, the ceramic particles can be selected from any one of the following: aluminum oxide, hydroxyaluminum oxide, silicon dioxide, silicon monoxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, carbon, zinc oxide, zirconium dioxide, zirconium hydroxide, barium oxide, niobium pentoxide, Li 1+x Al x Ge 2-x (PO 4 )3(0 ≤ x ≤ 0.65), Li 1+x Al x Ti 2-x (PO4)3(0 ≤ x ≤ 0.5), Li 7-x La3Zr 2-x Ta x O 12 (0 ≤ x ≤ 2), Na 1+x Zr2Si x P 3-x O 12 (0 ≤ x ≤ 3) and other types of ceramic particles, which can be specifically selected according to actual needs and are not limited here.

[0014] Moreover, the particle size of the ceramic particles can be set to 0.2 μm to 5 μm, and further can be set to 0.5 μm to 2 μm. For example but not limited to: 0.5 μm, 1.5 μm, 2 μm and other sizes. In this way, it is possible to avoid the weak bonding strength between particles caused by too large particle size of the ceramic particles, thereby avoiding the problem of ceramic particle shedding. It is also possible to avoid the high manufacturing cost and large manufacturing difficulty caused by the large grafting difficulty when the particle size of the ceramic particles is too small. Thus, on the basis of improving the stability of the battery separator, the manufacturing simplicity can also be improved.

[0015] In addition, in the ceramic particles, the difference between D50 and D90 can be set to 0.1 μm to 2 μm. For example but not limited to: 0.1 μm, 0.5 μm, 1.5 μm, 2 μm and other values, so as to reduce the particle size difference of the ceramic particles and improve the uniformity of the particle size of the ceramic particles. It should be understood that D50 can be understood as: the particle size corresponding to when the cumulative particle size distribution percentage reaches 50%, and D90 can be understood as: the particle size corresponding to when the cumulative particle size distribution number reaches 90%.

[0016] Optionally, the functional layer may further include a binder. The ceramic particles grafted with ionic conductive groups are bonded to the base film through the binder, thereby improving the bonding effect between the ceramic particles and the base film, avoiding the shedding of ceramic particles during use, and further avoiding the reduction of the performance of the battery separator. Among them, the ceramic particles grafted with ionic conductive groups can be called modified ceramic particles. At this time, the mass ratio of the modified ceramic particles to the binder can be set to 0.5 to 0.95, and further can be set to 0.7 - 0.9. For example but not limited to 0.7, 0.75, 0.8, 0.85, 0.9 and other values. In this way, the proportion of the modified ceramic particles is relatively large and the proportion of the binder is relatively small. This can avoid the reduction of the thermal stability, safety, wettability and ion mobility of the battery separator due to the relatively small proportion of the modified ceramic particles, and can also avoid the influence on the ion penetration efficiency in the battery separator when the proportion of the binder is relatively large. Therefore, limiting the mass ratio of the modified ceramic particles and the binder within a suitable range can not only improve the thermal stability, safety, wettability and ion mobility of the battery separator, but also improve the ion penetration efficiency in the battery separator, thereby improving the performance of the secondary battery.

[0017] Among them, the binder can be selected from at least one of the following: polyacrylate, polyvinylidene fluoride, polyvinylidene difluoride, polyvinylidene difluoride - co - hexafluoropropylene, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, polyethylene - co - vinyl acetate, polyimide, poly(ethylene oxide) and styrene - butadiene latex and other materials with bonding effects. Specifically, it can be selected according to actual needs and is not limited here.

[0018] Moreover, the thickness of the functional layer can be set to be from 2 μm to 10 μm, and further can be set to be from 2 μm to 5 μm, such as but not limited to: 2 μm, 3 μm, 4 μm, 5 μm and other thicknesses. In this way, it is possible to avoid affecting the ion passing efficiency when the functional layer is too thick, and it is also possible to avoid failing to achieve a good insulation effect when the functional layer is too thin. Therefore, setting the thickness of the functional layer within a suitable range can not only improve the ion passing efficiency, but also improve the insulation effect on the positive electrode and the negative electrode.

[0019] Optionally, the battery separator may further include an adhesive layer, which is disposed on the functional layer or on the surface of the base film without the functional layer. For example, the base film includes a first surface and a second surface opposite to each other. When the functional layer is disposed on the first surface, the adhesive layer may be disposed on the second surface and on the functional layer; or, when the functional layer is disposed on the first surface and the second surface, an adhesive layer is disposed on each functional layer. In this way, the adhesive layer can increase the stability of the functional layer on the surface of the base film, avoid the functional layer falling off or separating from the surface of the base film, and can also increase the firmness of the functional layer and avoid the functional layer from being damaged, thereby improving the reliability and stability of the battery separator. Among them, the thickness of the adhesive layer can be set to 0 - 5 μm, and further can be set to 0.5 μm - 2 μm, such as but not limited to: 0.5 μm, 1 μm, 1.5 μm, 2 μm and other thicknesses. This can avoid the adverse effect of too thick adhesive layer on improving the wettability and ion mobility of the functional layer, and can also avoid the inability to effectively protect the functional layer when the adhesive layer is too thin. Therefore, setting the adhesive layer within a suitable range can improve the reliability and stability of the battery separator. Moreover, the material for making the adhesive layer can be an inorganic material or an organic material, which can be specifically selected according to actual needs and is not limited herein.

[0020] In a second aspect, the embodiments of the present application further provide a battery separator, which may include: a base film, and a functional layer coated on at least one surface of the base film. The functional layer includes ceramic particles, and an ion conductive group is grafted onto the oxygen atoms on the surface of the ceramic particles, and M is selected from at least one of B, S, Si, C, and N. Compared with the ceramic particles, the ion conductive group is more likely to combine with the alkali metal ions in the electrolyte. Therefore, the Lewis acid-base interaction between the ceramic particles and the alkali metal ions in the electrolyte can be inhibited, and the ion mobility of the battery separator can be improved, thereby improving the charge and discharge rate performance of the secondary battery; and since the ion conductive group can provide solvation sites, the presence of the ion conductive group can improve the wettability of the battery separator with the electrolyte, so that the alkali metal ions can better contact the surface of the battery separator, and further the amount of alkali metal ions passing through the battery separator can be increased, the polarization phenomenon of the secondary battery can be reduced, and thus the charge and discharge capacity of the secondary battery can be improved, and the performance of the secondary battery can be improved.

[0021] It should be understood that since the principle of solving problems by this battery separator is similar to that of the aforementioned secondary battery, the implementation and technical effects of this battery separator can be referred to those of the aforementioned secondary battery, and the repeated parts will not be elaborated.

[0022] In a third aspect, an embodiment of the present application further provides a method for manufacturing a battery separator. This manufacturing method is used to manufacture the battery separator as described in any embodiment of the first aspect and the first aspect above or the battery separator introduced in the second aspect. This manufacturing method may include: mixing ceramic particles grafted with ion-conducting groups and a dispersant to obtain a slurry; coating the obtained slurry on at least one surface of a base film, and after treatment, the slurry forms a functional layer, thereby obtaining a battery separator. Thus, since the ceramic particles are grafted with ion-conducting groups on their surfaces, the ion mobility of the battery separator and its wettability with the electrolyte can be improved, thereby improving the performance of the secondary battery.

[0023] Optionally, the method for manufacturing ceramic particles grafted with ion-conducting groups includes: performing a condensation reaction or a substitution reaction on the ceramic particles and a compound containing an ion-conducting group and a leaving group, so that the hydrogen in the hydroxyl bond on the surface of the ceramic particles and the leaving group in the compound both leave, and then the ion-conducting group in the compound forms a bond with the oxygen in the hydroxyl bond, obtaining ceramic particles grafted with ion-conducting groups. Thus, ion-conducting groups can be grafted on the surface of the ceramic particles, thereby improving the wettability and ion mobility of the battery separator.

[0024] It should be understood that since the principle of solving problems by the battery separator manufactured by this manufacturing method is similar to that of the aforementioned battery separator, the implementation and technical effects of this manufacturing method can be referred to those of the aforementioned battery separator, and the repeated parts will not be elaborated.

[0025] In a fourth aspect, an embodiment of the present application further provides a battery pack. The battery pack may include: a box body and a plurality of secondary batteries. Each secondary battery is disposed in the box body, and the secondary battery is the secondary battery as described in any embodiment of the first aspect and the first aspect above. Thus, on the basis of improving the performance of the secondary battery, the performance of the battery pack will also be improved.

[0026] It should be understood that since the principle of solving problems by this battery pack is similar to that of the aforementioned secondary battery, the implementation and technical effects of this battery pack can be referred to those of the aforementioned secondary battery, and the repeated parts will not be elaborated.

[0027] Fifth aspect, the embodiments of the present application further provide an energy storage system, which includes a battery pack and a power converter as introduced in the fourth aspect above. The power converter is used to convert the alternating current output by an external AC power supply into direct current and output it to the battery pack, and / or, the power converter is used to convert the direct current output by the battery pack into alternating current and output it to a load or the power grid. In this way, on the basis of improving the performance of the battery pack, the performance of the energy storage system will also be improved.

[0028] It should be understood that since the principle of the energy storage system to solve problems is similar to that of the aforementioned battery pack, the implementation and technical effects of this energy storage system can refer to the implementation and technical effects of the aforementioned battery pack, and the repeated parts will not be elaborated. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic structural diagram of the energy storage system provided by the embodiments of the present application;

[0030] Figure 2 is a schematic structural diagram of the battery pack provided by the embodiments of the present application;

[0031] Figure 3 is a schematic structural diagram of the secondary battery provided by the embodiments of the present application;

[0032] Figure 4 is a schematic structural diagram of the battery separator provided by the embodiments of the present application;

[0033] Figure 5 is a scanning electron microscope image of the battery separator provided by the embodiments of the present application;

[0034] Figure 6 is an infrared spectrum diagram of the battery separator provided by the embodiments of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings.

[0036] It should be noted that the same reference numerals in the drawings of the present application represent the same or similar structures, and thus the repeated descriptions thereof will be omitted. The words expressing positions and directions in the present application are all described with reference to the drawings as examples, but can be changed according to needs, and all the changes made are included in the protection scope of the present application. The drawings of the present application are only used to illustrate the relative position relationship and do not represent the true proportion.

[0037] To facilitate the understanding of the technical solutions provided by the embodiments of the present application, the application scenarios thereof will be described first below.

[0038] The technical solution provided by the embodiments of the present application can be widely applied in an energy storage system, which can be applied to, but not limited to, scenarios such as household energy storage, site energy, intelligent photovoltaic, and data center energy, etc., for storing electric energy and supplying electric energy outward. Refer to Figure 1 the schematic structural diagram of the energy storage system shown in, the energy storage system may include: a battery cluster and a power converter 200. The battery cluster includes a plurality of battery packs 100 connected in series. Figure 1 Only one battery pack 100 is shown as an example. The power converter 200 can convert the alternating current output by an external alternating current power supply (such as the power grid 300) into direct current and output it to the battery pack 100 in the battery cluster to charge the battery pack 100, and can also convert the direct current output by the battery pack 100 in the battery cluster into alternating current and output it to the load 400 or the power grid 300 to discharge the battery pack 100.

[0039] Refer to Figure 2 the schematic structural diagram of the battery pack 100 shown in. The battery pack 100 may include: a box body 101 and a plurality of secondary batteries 102. Each secondary battery 102 is disposed in the box body 101. Each secondary battery 102 can be connected in series, in parallel, or in a combination of series and parallel connections, so that the battery pack 100 has a higher capacity and a higher voltage, and thus can be applicable to various application scenarios. Among them, for each secondary battery 102, as Figure 3 the schematic structural diagram of the secondary battery 102 shown in, the secondary battery 102 may include: a positive electrode 11, a negative electrode 12, a battery separator 13, and an electrolyte 14. The battery separator 13 is disposed between the positive electrode 11 and the negative electrode 12, and the electrolyte 14 infiltrates the positive electrode 11, the battery separator 13, and the negative electrode 12. And, the secondary battery can be, but not limited to: sodium ion battery, lithium ion battery, potassium ion battery or other types of secondary batteries. Taking the sodium ion battery as an example, when the sodium ion battery is charged, sodium ions are removed from the positive electrode 11, pass through the battery separator 13, and are embedded in the negative electrode 12; when the sodium ion battery is discharged, sodium ions are removed from the negative electrode 12, pass through the battery separator 13, and are embedded in the positive electrode 11; therefore, the amount of sodium ions embedded in the negative electrode 12 during charging affects the charging capacity of the sodium ion battery 102, and the amount of sodium ions embedded in the positive electrode 11 during discharging affects the discharging capacity of the sodium ion battery 102. Thus, the charging capacity and discharging capacity can be improved by improving the structures and manufacturing materials of the positive electrode 11 and the negative electrode 12; of course, the electronic insulation of the battery separator affects the isolation effect between the positive electrode and the negative electrode, and the ionic conductivity of the battery separator affects the passing efficiency of sodium ions, thereby affecting the internal resistance, rate charge and discharge, cycle life and safety of the sodium ion battery. Therefore, the performance of the battery separator also affects the performance of the sodium ion battery.

[0040] Based on this, the embodiments of the present application provide a battery separator, as Figure 4As shown, the battery separator may include: a base film, and a functional layer coated on at least one surface of the base film. The functional layer includes ceramic particles, and an M-containing ion-conducting group is grafted onto the oxygen atoms on the surface of the ceramic particles. M is selected from at least one of B, S, Si, C, and N. The ion-conducting group is such as Figure 4 -R in - A + As shown, R - contains M. Among them, compared with the ceramic particles, the ion-conducting group is more likely to combine with the alkali metal ions in the electrolyte. Therefore, the Lewis acid-base interaction between the ceramic particles and the alkali metal ions in the electrolyte can be inhibited, and the ion mobility of the battery separator can be improved, thereby improving the charge-discharge rate performance of the secondary battery. And because the ion-conducting group can provide solvation sites, the presence of the ion-conducting group can improve the wettability of the battery separator with the electrolyte, so that the alkali metal ions can better contact the surface of the battery separator, and then the amount of alkali metal ions passing through the battery separator can be increased, reducing the polarization phenomenon of the secondary battery, thereby improving the charge-discharge capacity of the secondary battery and improving the performance of the secondary battery.

[0041] In the ion-conducting group, M has a negative valence, so that there is a negative charge center in the ion-conducting group. When the battery separator is immersed in the electrolyte, the ion-conducting group is more likely to combine with the alkali metal ions in the electrolyte, so as to achieve the effect of increasing the wettability of the battery separator with the electrolyte and improving the ion mobility of the battery separator.

[0042] Furthermore, the ion-conducting group may be selected from any one of the following structures:

[0043]

[0044] Among them, R1 is selected from F or CF3, and R2 and R3 are each independently selected from: C2-C15 saturated hydrocarbons, or C2-C15 unsaturated hydrocarbons. Further, R2 and R3 are each independently selected from: C2-C6 saturated hydrocarbons, or C2-C6 unsaturated hydrocarbons, such as but not limited to: ethyl, vinyl, propyl, isopropyl, propenyl, isopropenyl, butyl, butenyl, pentyl, pentenyl, hexyl, hexenyl, phenyl and other groups, and the groups selected by R2 and R3 may be the same or different, and can be specifically selected according to actual needs, and are not limited herein. A is selected from any one of Li, Na, and K, and * represents the connection site of the ion-conducting group to the oxygen atom. Thus, when the battery separator is immersed in the electrolyte, the ion-conducting group can dissociate in the electrolyte, making the generated negative charge center more likely to combine with the alkali metal ions in the electrolyte, so as to further achieve the effect of increasing the wettability of the battery separator with the electrolyte and improving the ion mobility of the battery separator.

[0045] In the functional layer, the mass ratio of the ion-conductive group to the ceramic particles can be from 0.005 to 0.1, and further can be set to 0.04 - 0.1, such as but not limited to: 0.04, 0.06, 0.08, 0.1 and other values. In this way, the proportion of ceramic particles is relatively large and the proportion of ion-conductive groups is relatively small, which can avoid reducing the thermal stability and safety of the battery separator when the proportion of ceramic particles is small, and can also avoid increasing the grafting difficulty and grafting effect when the proportion of ion-conductive groups is large. Therefore, limiting the mass ratio of the ion-conductive group to the ceramic particles within a suitable range can not only make the battery separator have good thermal stability and safety, but also improve the wettability and ion mobility of the battery separator, as well as reduce the grafting difficulty and improve the grafting effect, thereby improving the performance of the secondary battery.

[0046] When grafting the ion-conductive group, the number of ion-conductive groups grafted on the surface of each ceramic particle can be from 1 to 8, such as but not limited to: 1, 2, 3, 4, 5, 6, 7, 8 and other values. In this way, a certain number of ion-conductive groups can be grafted on the surface of each ceramic particle, and it can also avoid the grafting process becoming more complex when the number of grafted ion-conductive groups is large, thereby avoiding an increase in manufacturing cost, and avoiding the difficulty of achieving the purpose of improving the wettability and ion mobility of the battery separator when the number of grafted ion-conductive groups is small.

[0047] Among them, the ceramic particles can be selected from any one of the following: aluminum oxide, hydroxyaluminum oxide, silicon dioxide, silicon monoxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, carbon, zinc oxide, zirconium dioxide, zirconium hydroxide, barium oxide, niobium pentoxide, Li 1+x Al x Ge 2-x (PO 4 )3(0 ≤ x ≤ 0.65), Li 1+x Al x Ti 2-x (PO4)3(0 ≤ x ≤ 0.5), Li 7-x La3Zr 2-x Ta x O 12 (0 ≤ x ≤ 2), Na 1+x Zr2Si x P 3-x O 12 (0 ≤ x ≤ 3) and other types of ceramic particles, and can be specifically selected according to actual needs, which is not limited here.

[0048] Moreover, the particle size of the ceramic particles can be set to 0.2 μm to 5 μm, and further can be set to 0.5 μm to 2 μm. For example, but not limited to: 0.5 μm, 1.5 μm, 2 μm and other sizes. In this way, it can be avoided that when the particle size of the ceramic particles is too large, the bonding strength between the particles is weak, thereby avoiding the problem of ceramic particle shedding. It can also avoid the high manufacturing cost and difficulty caused by the large grafting difficulty when the particle size of the ceramic particles is too small. Thus, on the basis of improving the stability of the battery separator, the manufacturing simplicity can also be improved.

[0049] In addition, in the ceramic particles, the difference between D50 and D90 can be set to 0.1 μm to 2 μm. For example, but not limited to: 0.1 μm, 0.5 μm, 1.5 μm, 2 μm and other values, so as to reduce the particle size difference of the ceramic particles and improve the uniformity of the particle size of the ceramic particles.

[0050] In addition to the ceramic particles, the functional layer can also include a binder. The ceramic particles grafted with ionic conductive groups are bonded to the base film through the binder, so as to improve the bonding effect between the ceramic particles and the base film, avoid the shedding of the ceramic particles during use, and further avoid the reduction of the performance of the battery separator. Among them, the ceramic particles grafted with ionic conductive groups can be called modified ceramic particles. At this time, the mass ratio of the modified ceramic particles to the binder can be set to 0.5 to 0.95, and further can be set to 0.7 - 0.9. For example, but not limited to 0.7, 0.75, 0.8, 0.85, 0.9 and other values. In this way, the proportion of the modified ceramic particles is relatively large and the proportion of the binder is relatively small. This can avoid the reduction of the thermal stability, safety, wettability and ion mobility of the battery separator due to the relatively small proportion of the modified ceramic particles, and can also avoid the influence on the ion passing efficiency in the battery separator when the proportion of the binder is relatively large. Therefore, limiting the mass ratio of the modified ceramic particles and the binder within a suitable range can not only improve the thermal stability, safety, wettability and ion mobility of the battery separator, but also improve the ion passing efficiency in the battery separator, thereby improving the performance of the secondary battery.

[0051] Among them, the binder can be selected from at least one of the following: polyacrylate, polyvinylidene fluoride, polyvinylidene difluoride, polyvinylidene difluoride - co - hexafluoropropylene, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, polyethylene - co - vinyl acetate, polyimide, poly(ethylene oxide) and styrene - butadiene latex and other materials with bonding effects. Specifically, it can be selected according to actual needs and is not limited here.

[0052] Moreover, the thickness of the functional layer can be set to 2 μm to 10 μm, and further can be set to 2 μm to 5 μm, such as but not limited to: 2 μm, 3 μm, 4 μm, 5 μm and other thicknesses. In this way, it is possible to avoid affecting the ion passing efficiency when the functional layer is too thick, and it is also possible to avoid the inability to achieve a good insulation effect when the functional layer is too thin. Therefore, setting the thickness of the functional layer within a suitable range can not only improve the ion passing efficiency, but also improve the insulation effect on the positive and negative electrodes.

[0053] The material for making the base film can be selected from polyolefin materials, such as but not limited to: polyethylene, polypropylene, and a composite of polypropylene / polyethylene / polypropylene, and the thickness of the base film can be set to 5 μm - 15 μm, and further can be set to 6 μm - 9 μm, such as but not limited to: 6 μm, 7 μm, 8 μm, 9 μm and other thicknesses. In this way, setting the thickness of the base film within a suitable range can avoid the too large thickness of the battery separator, thereby avoiding the too large size of the secondary battery, and can also avoid the easy damage of the battery separator when the base film is too thin, thereby avoiding the reduction of the stability of the battery separator. Moreover, the base film can have micropores, and ions can pass through the base film through the micropores, so as to achieve the purpose of ions passing through the battery separator and isolating electrons.

[0054] In addition to the base film and the functional layer, the battery separator can also include an adhesive layer, and the adhesive layer is provided on the functional layer or on the surface of the base film without the functional layer. For example, when the base film includes a first surface and a second surface opposite to each other, when the functional layer is provided on the first surface, the adhesive layer can be provided on the second surface and on the functional layer; or, when the functional layer is provided on the first surface and the second surface, an adhesive layer is provided on each functional layer. In this way, the stability of the functional layer on the surface of the base film can be increased through the adhesive layer, avoiding the functional layer from falling off or separating from the surface of the base film, and the firmness of the functional layer can also be increased, avoiding the functional layer from being damaged, thereby improving the reliability and stability of the battery separator. Among them, the thickness of the adhesive layer can be set to 0 - 5 μm, and further can be set to 0.5 μm - 2 μm, such as but not limited to: 0.5 μm, 1 μm, 1.5 μm, 2 μm and other thicknesses, which can avoid the adverse effects of too thick adhesive layer on improving the wettability and ion mobility of the functional layer, and can also avoid the inability to effectively protect the functional layer when the adhesive layer is too thin. Therefore, setting the adhesive layer within a suitable range can improve the reliability and stability of the battery separator. And the material for making the adhesive layer can be an inorganic material or an organic material, which can be specifically selected according to actual needs and is not limited here.

[0055] Next, the performance of the secondary battery is tested.

[0056] Fabrication of the secondary battery.

[0057] Example 1: The secondary battery is a lithium-ion battery. The ionic conductive group in the battery separator is -C6H4SO3Li, the positive electrode active material is LiNi 0.5 Mn 0.3 Co 0.2 O2, the negative electrode active material is graphite, and the lithium salt in the electrolyte is LiPF6.

[0058] The production process of the positive electrode includes: weighing the positive electrode active material, Super C, and polyvinylidene fluoride according to a certain mass ratio, and dispersing them in N-methyl-2-pyrrolidone as a dispersant to obtain a positive electrode slurry; uniformly coating the positive electrode slurry on both sides of the current collector, drying, calendaring, and vacuum drying, and welding the tab to obtain the positive electrode. Among them, Super C is a conductive agent, and polyvinylidene fluoride is an adhesive.

[0059] The production process of the negative electrode includes: weighing the negative electrode active material, Super C, sodium carboxymethyl cellulose, and styrene-butadiene rubber according to a certain mass ratio, and dispersing them in deionized water to obtain a negative electrode slurry; coating the negative electrode slurry on both sides of the current collector, drying, calendaring, and vacuum drying, and welding the tab to obtain the negative electrode. Among them, Super C is a conductive agent, and sodium carboxymethyl cellulose and styrene-butadiene rubber are adhesives.

[0060] The production process of the modified ceramic particles: weighing AlOOH, ClC6H4SO3Li, and an organic solvent according to a certain mass ratio, mixing them, and then carrying out a condensation reaction or a substitution reaction. After washing, purifying, filtering, and drying the reaction product, a powder is obtained. This powder is AlOOH grafted with -C6H4SO3Li, that is, the modified ceramic particles.

[0061] The production process of the battery separator includes: weighing the modified ceramic particles and the adhesive according to a certain mass ratio, mixing the two to form a slurry, coating it on both surfaces of the base film, drying, calendaring, and vacuum drying to form a functional layer; then coating a glue layer on the surface of the functional layer and drying again to obtain the battery separator.

[0062] The preparation and formation process of the battery cell includes: placing a battery separator with a certain thickness between the positive electrode and the negative electrode, then winding or laminating the sandwich structure composed of the positive electrode, the negative electrode, and the battery separator to prepare the battery cell, and then putting the wound core into a packaging bag, vacuum baking at a suitable temperature to obtain a dry battery cell to be filled with electrolyte; subsequently, in a drying room, injecting the electrolyte into the battery cell, vacuum packaging, leaving it at a suitable temperature for a certain period of time, and then carrying out formation and constant volume to obtain the sodium-ion battery.

[0063] Comparative Example 1: The secondary battery is a lithium-ion battery. No ceramic particles are provided in the battery separator, and the positive electrode active material is LiNi 0.5 Mn 0.3 Co0.2 The cathode active material is graphite, and the lithium salt in the electrolyte is LiPF6.

[0064] In Comparative Example 1, the manufacturing processes of the cathode and anode, as well as the preparation and formation processes of the battery cell, are the same as those in Example 1. For specific details, please refer to the relevant descriptions in Example 1 above, and the repeated parts will not be elaborated again. Also, since the ceramic particles are not provided on the battery separator in Comparative Example 1, the base film is used as the battery separator.

[0065] Example 2: The secondary battery is a sodium-ion battery. The ionic conductive group in the battery separator is -C6H4SO3Na, the cathode active material is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, the anode active material is hard carbon, and the sodium salt in the electrolyte is NaPF6.

[0066] In this Example 2, the manufacturing processes of the cathode, anode, modified ceramic particles, battery separator, as well as the preparation and formation processes of the battery cell are basically the same as those in Example 1. For specific details, please refer to the relevant descriptions in Example 1 above, and the repeated parts will not be elaborated again.

[0067] Example 3: The secondary battery is a sodium-ion battery. The ionic conductive group in the battery separator is -C6H4COONa, the cathode active material is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, the anode active material is hard carbon, and the sodium salt in the electrolyte is NaPF6.

[0068] In this Example 3, the manufacturing processes of the cathode, anode, modified ceramic particles, battery separator, as well as the preparation and formation processes of the battery cell are basically the same as those in Example 1. For specific details, please refer to the relevant descriptions in Example 1 above, and the repeated parts will not be elaborated again.

[0069] Comparative Example 2: The secondary battery is a sodium-ion battery. Ceramic particles are provided in the battery separator, but no ionic conductive group is grafted on the surface of the ceramic particles. The cathode active material is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, the anode active material is hard carbon, and the sodium salt in the electrolyte is NaPF6.

[0070] In Comparative Example 2, the manufacturing processes of the positive electrode, negative electrode, the manufacturing process of the battery separator, and the preparation and formation processes of the battery cell are substantially the same as the relevant content in Example 1, except that the ceramic particles added to the battery separator are unmodified ceramic particles, and the others are the same. For specific details, reference can be made to the relevant introduction in the aforementioned Example 1, and the repeated parts will not be elaborated here.

[0071] Characterization of the battery separator:

[0072] The battery separator produced in Example 2 was characterized by scanning electron microscopy, as Figure 5 shown. It can be seen from Figure 5 that the surface morphology of the battery separator is relatively complete and effectively covers the base film. Moreover, the battery separator in Example 2 was tested by infrared spectroscopy, and the test results are as Figure 6 shown. It was found from Figure 6 that the transmission peak appearing at 1300 - 1320 cm -1 corresponds to the sulfonic group, and the transmission peak appearing at 480 cm -1 corresponds to O=Al-OH. This indicates that the battery separator contains ceramic particles and ion conductive groups, and washing and purification treatments were carried out during the production of the modified ceramic particles, so the un-grafted ion conductive groups have basically been washed away. The remaining ion conductive groups can be considered to have been grafted onto the surface of the ceramic particles. Therefore, when the sulfonic group is detected, it can be determined that the ion conductive groups are grafted onto the oxygen atoms on the surface of the ceramic particles, thus indicating that the ceramic particles in the battery separator are modified ceramic particles.

[0073] Performance test:

[0074] By performing capacity tests and rate performance tests on Examples 1 to 3, as well as Comparative Example 1 and Comparative Example 2, the test results shown in Table 1 below can be obtained. Among them, the MacMullin value refers to the ratio of the ionic conductivity of the electrolyte without a battery separator to the ionic conductivity of the electrolyte with a battery separator, and the larger the MacMullin value, the worse the ion mobility, and the smaller the MacMullin value, the higher the ion mobility; the Gurley value refers to the time required for a certain amount of air to pass through a battery separator with a specific area under a specific pressure, and the larger the Gurley value, the worse the air permeability of the battery separator, and the smaller the Gurley value, the better the penetrability of the battery separator; the thermal shrinkage rate refers to the ratio of the dimensional change value of the battery separator in a certain direction after being placed at 130 °C for 1 h to the original value (i.e., the value in the same direction of the just-made battery separator), and the smaller this ratio, the smaller the shrinkage degree of the battery separator in a certain direction at high temperature, and the larger this ratio, the larger the shrinkage degree of the battery separator in a certain direction at high temperature; MD and TD represent two mutually perpendicular directions; the cycle capacity retention rate at room temperature refers to: at room temperature, such as but not limited to 25 °C, the discharge capacity retention rate of the secondary battery after 1000 cycles of charge and discharge, and the cycle capacity retention rate at high temperature refers to: at high temperature, such as but not limited to 45 °C, the discharge capacity retention rate of the secondary battery after 1000 cycles of charge and discharge.

[0075] Table 1

[0076]

[0077] From the test results shown in Table 1 above, it can be found that:

[0078] (1) From the test results of the contact angle, the contact angles of Examples 1 to 3 are all 0°, while the contact angles of Comparative Example 1 and Comparative Example 2 are both greater than 0°. This shows that when modified ceramic particles are provided in the battery separator, the contact angle of the battery separator can be effectively reduced, and the wettability of the battery separator in the electrolyte can be improved.

[0079] (2) From the test results of the MacMullin values, the MacMullin values of Examples 1 to 3 are 3.5 to 4.3, while the MacMullin values of Comparative Examples 1 and 2 are at least 8.9. Therefore, the MacMullin values of Examples 1 to 3 are smaller, indicating that when modified ceramic particles are provided in the battery separator, the ion mobility of the battery separator can be effectively improved. Moreover, the MacMullin value of Example 3 is greater than that of Example 2 because the binding strength between the carboxylate ion in -C6H4COONa and the alkali metal ion is greater than the binding strength between the sulfite ion in -C6H4SO3Na and the alkali metal ion. Therefore, the dissociation degree of -C6H4COONa in the electrolyte is smaller, and thus the amount of carboxylate ions in the electrolyte is smaller, and then the amount of alkali metal ions that can be bound in the electrolyte is also smaller, ultimately resulting in a worse ion mobility in Example 3 than in Example 2.

[0080] (3) From the test results of the Gurley values, the Gurley values of Examples 1 to 3 and Comparative Example 2 are 230 - 260, while the Gurley value of Comparative Example 1 is 220. Although the Gurley value of Comparative Example 1 is smaller, the difference from the Gurley values of Examples 1 to 3 and Comparative Example 2 is not very large, indicating that when ceramic particles are provided in the battery separator, the air permeability of the battery separator can be reduced, but the degree of reduction is limited and will not have too much impact on the air permeability of the battery separator. Moreover, the Gurley values of Examples 1 to 3 and Comparative Example 2 are relatively close, indicating that the influence of modified ceramic particles and unmodified ceramic particles on the air permeability of the battery separator is not very different, and the influence of different ion conductive groups on the air permeability of the battery separator is not very different.

[0081] (4) From the test results of the thermal shrinkage rate, compared with Comparative Example 1, the thermal shrinkage rates of Examples 1 to 3 and Comparative Example 2 are smaller, indicating that the shrinkage degree of the battery separators in Examples 1 to 3 and Comparative Example 2 at high temperature is smaller. This is because the ceramic particles can inhibit the shrinkage of the battery separator, so the presence of the ceramic particles can reduce the shrinkage of the battery separator at high temperature, making the battery separator have better stability. Moreover, the thermal shrinkage rates of Examples 1 to 3 and Comparative Example 2 are close or even the same, indicating that the shrinkage degrees of the battery separators in Examples 1 to 3 and Comparative Example 2 at high temperature are similar. Furthermore, it shows that compared with unmodified ceramic particles, the influence of modified ceramic particles on the shrinkage degree is less different, and the influence of different ion conductive groups on the shrinkage degree is also less different.

[0082] (5) Both Example 1 and Comparative Example 1 are lithium-ion batteries. Comparing the test results of the two, whether at room temperature or at high temperature, the cycle capacity retention rate of the lithium-ion battery in Example 1 is higher than that in Comparative Example 1. This shows that when ceramic particles are provided in the battery separator and ionic conductive groups are grafted on the surface of the ceramic particles, the wettability of the battery separator in the electrolyte and the ion mobility can be improved, thereby improving the penetration efficiency of lithium ions in the battery separator, increasing the amount of lithium ions embedded and extracted, and thus improving the capacity retention rate of the lithium-ion battery.

[0083] (6) Both Example 2, Example 3 and Comparative Example 2 are sodium-ion batteries. Comparing the test results of the three, whether at room temperature or at high temperature, the cycle capacity retention rates of the lithium-ion batteries in Example 2 and Example 3 are higher than that in Comparative Example 2. This shows that when modified ceramic particles are provided in the battery separator, the wettability of the battery separator in the electrolyte and the ion mobility can be improved, thereby improving the penetration efficiency of lithium ions in the battery separator, increasing the amount of lithium ions embedded and extracted, and thus improving the capacity retention rate of the lithium-ion battery.

[0084] (7) Whether at room temperature or at high temperature, the capacity retention rate of Example 2 is slightly higher than that of Example 3. This is because the stability of -C6H4SO3Na is higher than that of -C6H4COONa. Therefore, the ceramic particles grafted with -C6H4SO3Na are more stable, making the battery separator more stable, and further making the performance of the secondary battery more stable, thereby improving the capacity retention rate.

[0085] Obviously, those skilled in the art can make various changes and modifications to the embodiments of the present application without departing from the spirit and scope of the embodiments of the present application. Thus, if these modifications and variations of the embodiments of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these changes and modifications.

Claims

1. A secondary battery, characterized in that, It includes a battery separator, and the battery separator includes: a base film, and a functional layer coated on at least one surface of the base film. The functional layer includes ceramic particles, and an ion-conductive group containing M is grafted onto the oxygen atoms on the surface of the ceramic particles. M is selected from at least one of B, S, Si, C, and N.

2. The secondary battery according to claim 1, characterized in that, The M is negatively charged.

3. The secondary battery according to claim 1 or 2, characterized in that, The ion-conductive group is selected from any one of the following structures: Wherein, R1 is selected from F or CF3, R2 and R3 are each independently selected from: C2-C15 saturated hydrocarbons, or C2-C15 unsaturated hydrocarbons, A is selected from: any one of Li, Na, and K, and * represents the connection site of the ion-conductive group to the oxygen atom.

4. The secondary battery according to any one of claims 1-3, characterized in that, The mass ratio of the ion-conductive group to the ceramic particles is 0.005 to 0.

1.

5. The secondary battery according to any one of claims 1-4, characterized in that, The number of the ion-conductive groups grafted on the surface of each ceramic particle is 1 to 8.

6. The secondary battery according to any one of claims 1-5, characterized in that, The ceramic particles are selected from any one of the following: aluminum oxide, hydroxyaluminum oxide, silicon dioxide, silicon monoxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, carbon, zinc oxide, zirconium dioxide, zirconium hydroxide, barium oxide, niobium pentoxide, Li 1+x Al x Ge 2-x (PO 4 )3(0 ≤ x ≤ 0.65), Li 1+ x Al x Ti 2-x (PO4)3(0 ≤ x ≤ 0.5), Li 7-x La3Zr 2-x Ta x O 12 (0 ≤ x ≤ 2), Na 1+x Zr2Si x P 3-x O 12 (0 ≤ x ≤ 3).

7. The secondary battery according to any one of claims 1-6, characterized in that, The functional layer further includes a binder, and the ceramic particles grafted with the ion-conductive groups are bonded to the base film through the binder. The mass ratio of the ceramic particles grafted with the ion-conductive groups to the binder is 0.5 to 0.

95.

8. The secondary battery according to claim 7, characterized in that, The binder is selected from at least one of the following: polyacrylate, polyvinylidene fluoride, polyvinylidene difluoride, polyvinylidene difluoride-co-hexafluoropropylene, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, polyethylene-co-vinyl acetate, polyimide, poly(ethylene oxide), and styrene-butadiene latex.

9. The secondary battery according to any one of claims 1-8, characterized in that, The battery separator further includes an adhesive layer, and the adhesive layer is disposed on the functional layer or on the surface of the base film without the functional layer.

10. A battery separator, characterized in that, It includes: A base film, and a functional layer coated on at least one surface of the base film. The functional layer includes ceramic particles, and an ion-conductive group is grafted onto the oxygen atoms on the surface of the ceramic particles. M is selected from at least one of B, S, Si, C, and N.

11. A battery pack, characterized in that, It includes: A box body, and a plurality of secondary batteries as described in any one of claims 1-9, and each of the secondary batteries is disposed in the box body.

12. An energy storage system, characterized in that, The energy storage system includes the battery pack as described in claim 11 above and a power converter. The power converter is used to convert the alternating current output by an external alternating current power supply into direct current and output it to the battery pack, and / or, the power converter is used to convert the direct current output by the battery pack into alternating current and output it to a load or the power grid.

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