Secondary battery and electric device

Abstract

A secondary battery and an electric device. The secondary battery comprises a composite separator and an electrolyte. The composite separator comprises a base membrane and a functional resin layer arranged on the surface of the base membrane. The functional resin layer comprises a functional polymer. The functional polymer contains an iminodiacetate group. Cations of the iminodiacetate group include at least one of Li+, Na+, and K+. At 25°C, the conductivity of the electrolyte is greater than or equal to 5 mS / cm.

Description

Secondary batteries and electrical devices

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202311493719.9, filed on November 9, 2023, entitled “Secondary Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a secondary battery and an electrical device. Background Art

[0004] Secondary batteries, such as lithium-ion batteries, are gaining increasing popularity due to their clean and renewable nature. They have been widely applied in consumer electronics, electric vehicles, and energy storage, among other fields. These batteries rely primarily on the movement of ions between the positive and negative electrodes. A separator membrane is placed between the positive and negative electrodes to isolate them, preventing short circuits within the battery. As the application of secondary batteries continues to expand, the membrane is wetted by the electrolyte, forming a channel for ion migration.

[0005] As the application scope of secondary batteries continues to expand, performance requirements for them are becoming increasingly stringent, such as the pursuit of higher energy density. Consequently, the use of high-voltage cathode materials to achieve higher energy density has become a trend. However, when batteries are operated at high voltages, the cathode material structure tends to become unstable and prone to structural collapse, directly leading to the dissolution of large amounts of transition metal ions. These dissolved transition metal ions may deposit at the anode or catalyze the decomposition of the anode interface film and electrolyte components. There is also the risk of dendrite growth, which could pierce the separator and cause cell failure. This significantly limits the cycle performance and storage stability of secondary batteries.

[0006] Therefore, the traditional technology needs to be further improved.

[0007] Summary of the Invention

[0008] According to various embodiments of the present application, the present application provides a secondary battery and an electrical device, aiming to improve the cycle performance and storage stability of the secondary battery.

[0009] This application is achieved through the following technical solutions.

[0010] In a first aspect of the present application, a secondary battery is provided, comprising a composite separator and an electrolyte;

[0011] The composite isolation membrane includes a base membrane and a functional resin layer provided on the surface of the base membrane, wherein the functional resin layer includes a functional polymer, the functional polymer contains an iminodiacetate group, and the cation of the iminodiacetate group includes Li + 、Na + and K + At least one of;

[0012] At 25° C., the conductivity of the electrolyte is greater than or equal to 5 mS / cm.

[0013] In the above-mentioned secondary battery, on the one hand, a composite separator with a specific structure is used, and the functional resin layer of the composite separator contains iminodiacetate groups that can directional capture transition metal ions, wherein the iminodiacetate groups are fixed on the surface of the composite separator through the functional resin layer, and the Li contained in the iminodiacetate groups + 、Na + , K + Cations such as cations exchange with transition metal ions, thereby fixing transition metal ions in the electrolyte on the surface of the composite separator, reducing their chance of being trapped at the electrode or dispersed in the electrolyte. Furthermore, during the ion exchange process between the cations in the iminodiacetate groups in the functional resin layer and the transition metal ions in the electrolyte, the iminodiacetate groups dissociate into cations, becoming electronegative. This repels the anions of the electrolyte salt in the electrolyte while simultaneously attracting active ions such as lithium ions. This inhibits the transport of anions and cations between the positive and negative electrodes during charge and discharge, increasing polarization. Therefore, by simultaneously controlling the conductivity of the electrolyte, the dissociation ability of the electrolyte solvent towards the electrolyte salt is enhanced, promoting the transport of anions and cations in the electrolyte. In this way, these two aspects work together to achieve targeted capture of transition metal ions while maintaining a good ion transport rate, effectively improving the cycling performance and storage stability of the secondary battery.

[0014] In some embodiments, the iminodiacetate group is represented by formula (1):

[0015] Among them, X + and Y + are independently selected from H + 、Li + 、Na + , K + Any one of the above, and X + and Y + Not H at the same time + ;

[0016] * is the connection site.

[0017] In some embodiments, the side chains of the functional polymer are grafted with the iminodiacetate groups.

[0018] By grafting iminodiacetate groups on the side chains, the iminodiacetate groups are introduced into the functional polymer, so that the iminodiacetate groups form a chemical bond with the polymer, so that the iminodiacetate groups are more stably fixed on the functional resin layer, reducing the chance of them dissociating and dispersing into the electrolyte.

[0019] In some embodiments, the functional polymer has a volume distribution particle size Dv50 of 100 nm to 1200 nm;

[0020] Optionally, the volume distribution particle size Dv50 of the functional polymer is 100 nm to 1000 nm;

[0021] Further optionally, the volume distribution particle size Dv50 of the functional polymer is 200 nm to 600 nm.

[0022] By regulating the volume distribution particle size of the functional polymer, on the one hand, the polymer maintains a larger specific surface area and increases the sites of the iminodiacetic acid salt groups exposed on the surface of the functional resin, thereby improving the capture efficiency of the functional resin layer for transition metal ions in the electrolyte. On the other hand, the functional polymers in the functional resin layer still form a certain gap after accumulation, which is equivalent to the functional resin layer retaining a certain porosity, thereby improving the ion migration efficiency formed after the composite isolation membrane is wetted by the electrolyte, thereby further improving the cycle performance of the secondary battery.

[0023] In some embodiments, the functional polymer satisfies at least one of the following conditions (1) to (3):

[0024] (1) The raw materials for preparing the main chain of the functional polymer include at least one of an acrylic monomer and styrene;

[0025] Acrylic acid polymer chains or styrene polymer chains have the advantages of many pores and large specific surface area, and have strong adsorption energy for electrolytes, which can enable the iminodiacetic acid salt groups to fully contact the electrolyte, quickly capture transition metal ions, and reduce the probability of transition metals migrating too quickly and depositing on the negative electrode. At the same time, they also have good acid and alkali resistance, strong redox stability and small expansion and contraction, which can improve the stability of the composite separator and further improve the performance of the secondary battery.

[0026] (2) The functional polymer is a cross-linked polymer;

[0027] The cross-linked polymer has better mechanical strength and can further improve the stability of the composite isolation membrane.

[0028] (3) In the functional resin layer, the mass proportion of the functional polymer is 80% to 95%.

[0029] In some embodiments, the mass content of hydrofluoric acid in the electrolyte is less than or equal to 300 ppm.

[0030] Hydrofluoric acid itself is corrosive and can negatively impact the performance of secondary batteries. Furthermore, hydrofluoric acid dissociates into hydrogen ions in the electrolyte, which then exchange with iminodiacetate groups to form stable iminodiacetic acid groups, which are detrimental to the capture of transition metal ions. Therefore, further controlling the hydrofluoric acid content in the electrolyte can improve the efficiency of the composite separator in capturing transition metal ions.

[0031] In some embodiments, the components of the electrolyte include an electrolyte salt and a solvent, the solvent includes a cyclic carbonate, and the mass proportion of the cyclic carbonate in the solvent is less than 50%;

[0032] Optionally, the mass proportion of the cyclic carbonate in the solvent is 5% to 46%;

[0033] On the one hand, the type of solvent in the electrolyte is adjusted. The cyclic carbonate has an excellent ability to promote the dissociation of the electrolyte salt, which is beneficial to improving the conductivity of the electrolyte. At the same time, its content is controlled to reduce the viscosity of the electrolyte, further promote the dissociation of the electrolyte salt, and improve the wettability of the electrolyte to the composite isolation membrane, thereby improving the capture efficiency of the composite isolation membrane for transition metal ions.

[0034] Further optionally, the cyclic carbonate includes at least one of ethylene carbonate, vinylene carbonate, propylene carbonate, butylene carbonate and fluoroethylene carbonate.

[0035] In some embodiments, the electrolyte satisfies at least one of the following conditions (1) to (2):

[0036] (1) The solvent also includes a chain ester solvent;

[0037] Chain ester solvents are beneficial for reducing the viscosity of the electrolyte and further improving the ion conductivity of the electrolyte.

[0038] Optionally, the chain ester solvent includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate and propyl propionate;

[0039] (2) The concentration of the electrolyte salt is 0.5 mol / L to 2 mol / L.

[0040] In some embodiments, the components of the electrolyte further include functional additives;

[0041] Optionally, the mass of the functional additive accounts for 2% to 15% of the total mass of the electrolyte.

[0042] In some embodiments, the functional additive includes at least one of a film-forming additive and a complexing additive;

[0043] Optionally, the film-forming additive includes at least one of a sulfate film-forming additive, a sulfite film-forming additive, a sultone film-forming additive, a disulfonic acid film-forming additive, an aromatic film-forming additive, an isocyanate film-forming additive, a phosphite film-forming additive, a phosphate film-forming additive, and a borate film-forming additive;

[0044] Optionally, the complexing additive includes at least one of a nitrile complexing additive, a crown ether complexing additive, and an oxime complexing additive.

[0045] Film-forming additives can form a protective layer at the interface of the electrode sheet, reducing the corrosion of the electrolyte; complexing additives can complex with the transition metals on the surface of the active material, improve the stability of the active material surface during the charge and discharge process, and reduce the dissolution of transition metals caused by surface structure degradation.

[0046] In some embodiments, the functional resin layer satisfies at least one of the following conditions (1) to (2):

[0047] (1) 1 g of the functional resin layer contains 0.2 mg to 5 mg of the cation;

[0048] (2) The thickness of the functional resin layer is 1 μm to 50 μm;

[0049] Optionally, the thickness of the functional resin layer is 2 μm to 30 μm;

[0050] Further optionally, the thickness of the functional resin layer is 5 μm to 20 μm.

[0051] In some embodiments, the secondary battery further includes a positive electrode sheet and a negative electrode sheet, the composite isolation membrane is arranged between the positive electrode sheet and the negative electrode sheet, and in the composite isolation membrane, the functional resin layer is provided on at least the surface of the side of the base membrane closer to the positive electrode sheet.

[0052] During the charge and discharge process of a secondary battery, the negative electrode is at a lower potential than the positive electrode. At this low potential, transition metal ions captured by the iminodiacetate groups are easily attracted by the electric field, causing a small amount of desorption and deposition at the negative electrode, reducing the composite separator's adsorption efficiency for transition metal ions. Therefore, a functional resin layer is provided on at least one side of the base film closer to the positive electrode to enhance the composite separator's adsorption efficiency for transition metal ions.

[0053] According to a second aspect of the present application, there is provided an electric device, comprising the secondary battery according to the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive work. In the drawings:

[0055] FIG1 is a schematic diagram of an embodiment of a battery cell;

[0056] Figure 2 is an exploded view of Figure 1;

[0057] FIG3 is a schematic diagram of an embodiment of a battery pack;

[0058] FIG4 is an exploded view of FIG3 ;

[0059] FIG. 5 is a schematic diagram of an embodiment of an electric device using a battery as a power source.

[0060] Explanation of the accompanying reference numerals: 1. battery pack; 2. upper box; 3. lower box; 4. battery cell; 41. shell; 42. electrode assembly; 43. cover plate; 5. electrical device. DETAILED DESCRIPTION

[0061] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0062] In the description of the embodiments of the present application, “multiple” means two or more, unless otherwise clearly and specifically defined.

[0063] In this application, "room temperature" generally refers to 4°C to 30°C, preferably 20±5°C.

[0064] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0065] As mentioned in the background art, transition metal ions released during the charge and discharge process of secondary batteries severely limit the improvement of the cycle storage performance of secondary batteries. Conventional technologies attempt to introduce chelating functional groups such as iminodiacetate groups that can adsorb transition metal ions into the separator.

[0066] Chelating functional groups typically chelate transition metal ions by dissociating into alkali metal cations and exchanging ions with transition metal ions. However, research has found that during the process of chelating and capturing transition metal ions, the chelating functional groups dissociate into cations that become electronegative. This repel the anions of the electrolyte salt in the electrolyte while attracting active ions such as lithium ions. This inhibits the transport of anions and cations between the positive and negative electrodes during charge and discharge, increases polarization, and in turn deteriorates the performance of the secondary battery.

[0067] Therefore, one embodiment of the present application provides a secondary battery, which includes a composite separator and an electrolyte.

[0068] The composite isolation membrane comprises a base membrane and a functional resin layer provided on the surface of the base membrane, wherein the functional resin layer comprises a functional polymer, the functional polymer comprises an iminodiacetate group, and the cation of the iminodiacetate group comprises Li + 、Na + and K + At least one of .

[0069] At 25° C., the conductivity of the electrolyte is greater than or equal to 5 mS / cm.

[0070] In the above-mentioned secondary battery, on the one hand, a composite separator with a specific structure is used, and the functional resin layer of the composite separator contains iminodiacetate groups that can directional capture transition metal ions, wherein the iminodiacetate groups are fixed on the surface of the composite separator through the functional resin layer, and the Li contained in the iminodiacetate groups + 、Na + , K +Cations such as cations exchange with transition metal ions, thereby fixing transition metal ions in the electrolyte on the surface of the composite separator, reducing their chance of being trapped at the electrode or dispersed in the electrolyte. Furthermore, during the ion exchange process between the cations in the iminodiacetate groups in the functional resin layer and the transition metal ions in the electrolyte, the iminodiacetate groups dissociate into cations, becoming electronegative. This repels the anions of the electrolyte salt in the electrolyte while simultaneously attracting active ions such as lithium ions. This inhibits the transport of anions and cations between the positive and negative electrodes during charge and discharge, increasing polarization. Therefore, by simultaneously controlling the conductivity of the electrolyte, the dissociation ability of the electrolyte solvent towards the electrolyte salt is enhanced, promoting the transport of anions and cations in the electrolyte. In this way, these two aspects work together to achieve targeted capture of transition metal ions while maintaining a good ion transport rate, effectively improving the cycling performance and storage stability of the secondary battery.

[0071] In some embodiments, at 25° C., the conductivity of the electrolyte is 5 mS / cm to 9 mS / cm.

[0072] In some embodiments, the iminodiacetate group is represented by formula (1):

[0073] Among them, X + and Y + are independently selected from H + 、Li + 、Na + , K + Any one of the above, and X + and Y + Not H at the same time + ;

[0074] * is the connection site.

[0075] In some embodiments, the side chains of the functional polymer are grafted with the iminodiacetate groups.

[0076] By grafting iminodiacetate groups on the side chains, the iminodiacetate groups are introduced into the functional polymer, so that the iminodiacetate groups form a chemical bond with the polymer, so that the iminodiacetate groups are more stably fixed on the functional resin layer, reducing the chance of them dissociating and dispersing into the electrolyte.

[0077] It can be understood that the functional polymer mainly includes a main molecular chain and side chains connected to the carbon atoms of the main chain, and the iminodiacetate groups are introduced into the functional polymer by grafting iminodiacetate groups on the side chains.

[0078] In some embodiments, the volume distribution particle size Dv50 of the functional polymer is 100 nm to 1200 nm.

[0079] In some embodiments, the volume distribution particle size Dv50 of the functional polymer is 100 nm to 1000 nm.

[0080] In some embodiments, the volume distribution particle size Dv50 of the functional polymer is 200 nm to 600 nm.

[0081] By regulating the volume distribution particle size of the functional polymer, on the one hand, the polymer maintains a larger specific surface area and increases the sites of the iminodiacetic acid salt groups exposed on the surface of the functional resin, thereby improving the efficiency of the functional resin layer in capturing transition metal ions in the electrolyte. On the other hand, the functional polymers in the functional resin layer are accumulated and aggregated to form a certain gap, which is equivalent to the functional resin layer retaining a certain porosity, thereby improving the ion migration efficiency formed after the composite isolation membrane is wetted by the electrolyte, thereby further improving the cycle performance of the secondary battery.

[0082] In the present application, the above-mentioned Dv50 is: the particle size corresponding to 50% volume distribution in the particle size-volume cumulative distribution curve, which can be obtained based on the volume cumulative distribution curve. As an example, it can be carried out with reference to the relevant standards of GB / T19077-2016 / ISO 13320:2009 and conveniently measured using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Co., Ltd. in the United Kingdom.

[0083] Refer to GB / T19077-2016 / ISO 13320:2009 standard process, the specific testing process is as follows:

[0084] Take an appropriate amount of the sample to be tested and add it to deionized water to ensure that the sample concentration is 8% to 12% shading. At the same time, ultrasonicate for 5 minutes to ensure that the sample is completely dispersed. Then, measure the sample according to GB / T19077-2016 / ISO13320:2009 standard.

[0085] The frequency of ultrasound is 53KHz and the power is 120W.

[0086] In the above “100nm~1000nm”, the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and the following point values: 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 850nm, 900nm, 950nm, 1000nm; or a range consisting of any two values, for example: 100nm~150nm, 100nm~250nm, 100nm~350nm, 100nm~450nm, 100nm~550nm, 100nm~650nm, 100nm~750nm, 100nm~850nm, 100nm~950nm m, 200nm~250nm, 200nm~350nm, 200nm~450nm, 200nm~550nm, 200nm~650nm, 200nm~750nm, 200n m~850nm, 200nm~950nm, 300nm~350nm, 300nm~450nm, 300nm~550nm, 300nm~650nm, 300nm~750nm , 300nm~850nm, 300nm~950nm, 400nm~450nm, 400nm~550nm, 400nm~650nm, 400nm~750nm, 400nm ~850nm, 400nm~950nm, 500nm~550nm, 500nm~650nm, 500nm~750nm, 500nm~850nm, 500nm~950nm.

[0087] In some embodiments, the raw materials for preparing the main chain of the functional polymer include at least one of acrylic monomers and styrene.

[0088] Acrylic acid polymer chains or styrene polymer chains have the advantages of many pores and large specific surface area, and have strong adsorption energy for electrolytes, which can enable the iminodiacetic acid salt groups to fully contact the electrolyte, quickly capture transition metal ions, and reduce the probability of transition metals migrating too quickly and depositing on the negative electrode. At the same time, they also have good acid and alkali resistance, strong redox stability and small expansion and contraction, which can improve the stability of the composite separator and further improve the performance of the secondary battery.

[0089] In some embodiments, the acrylic monomer includes at least one of acrylic acid, acrylic acid homologues, and acrylic acid ester compounds.

[0090] Furthermore, the acrylic monomer has the following structure:

[0091] Here, each R1 is independently selected from a chain alkyl group having 1 to 5 carbon atoms.

[0092] In some embodiments, each R1 is independently selected from a chain alkyl group having 1 to 3 carbon atoms.

[0093] In some embodiments, the acrylic monomer includes at least one of acrylic acid and methacrylic acid.

[0094] In some embodiments, the functional polymer is a cross-linked polymer.

[0095] The cross-linked polymer has better mechanical strength and can further improve the stability of the composite isolation membrane.

[0096] In some embodiments, in the functional resin layer, the weight percentage of the functional polymer is 80% to 95%.

[0097] In the above "80% to 95%", the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and the following point values: 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%; or a range consisting of any two values, for example: 80% to 95%, 83% to 95%, 85% to 95%, 90% to 95%.

[0098] In some embodiments, the component of the functional resin layer includes a binder.

[0099] The binder can further improve the stability of the composite separator.

[0100] The binder can be various types of binders commonly used in the art, including polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, hydrogenated nitrile rubber, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS) and at least one of fluorine-containing acrylate resins.

[0101] In some embodiments, the binder accounts for 5% to 20% by mass in the functional resin layer.

[0102] In the above-mentioned "5% to 20%", the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and the following point values: 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%; or a range consisting of any two values, for example: 5% to 20%, 10% to 20%, 15% to 20%, 5% to 15%.

[0103] In some embodiments, the mass content of hydrofluoric acid in the electrolyte is less than or equal to 300 ppm.

[0104] Hydrofluoric acid itself is corrosive and can negatively impact the performance of secondary batteries. Furthermore, hydrofluoric acid dissociates into hydrogen ions in the electrolyte, which then exchange with iminodiacetate groups to form stable iminodiacetic acid groups, which are detrimental to the capture of transition metal ions. Therefore, further controlling the hydrofluoric acid content in the electrolyte can improve the efficiency of the composite separator in capturing transition metal ions.

[0105] In some embodiments, the components of the electrolyte include an electrolyte salt and a solvent, the solvent includes a cyclic carbonate, and the mass proportion of the cyclic carbonate in the solvent is less than 50%.

[0106] In some embodiments, the mass proportion of the cyclic carbonate in the solvent is 5% to 46%.

[0107] On the one hand, the type of electrolyte solvent is adjusted. The ability of cyclic carbonate to promote the dissociation of electrolyte salt is excellent, which is beneficial to improve the conductivity of the electrolyte. At the same time, its content is controlled to reduce the viscosity of the electrolyte, further promote the dissociation of electrolyte salt, and improve the wettability of the electrolyte to the composite isolation membrane, thereby improving the capture efficiency of the composite isolation membrane for transition metal ions.

[0108] In the above “5% to 46%”, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and the following point values: 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, %, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 45.5%, 46%; or a range consisting of any two values, for example: 5% to 45%, 10% to 45%, 25% to 45%, 15% to 40%, 20% to 40%.

[0109] In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate, vinylene carbonate, propylene carbonate, butylene carbonate, and fluoroethylene carbonate.

[0110] In some embodiments, the solvent further comprises a chain ester solvent.

[0111] Chain ester solvents are beneficial for reducing the viscosity of the electrolyte and further improving the ion conductivity of the electrolyte.

[0112] In some embodiments, the chain ester solvent includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, and propyl propionate.

[0113] In some embodiments, the mass proportion of the cyclic carbonate in the solvent is 55% to 95%.

[0114] In some embodiments, the concentration of the electrolyte salt is 0.5 mol / L to 2 mol / L.

[0115] In some embodiments, the components of the electrolyte further include functional additives;

[0116] Optionally, the mass of the functional additive accounts for 2% to 15% of the total mass of the electrolyte.

[0117] In the above-mentioned "2% to 15%", the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and the following point values: 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%; or a range consisting of any two values, for example: 5% to 15%, 10% to 15%, 2% to 10%, 2% to 5%.

[0118] The functional additives in this application can be any electrolyte additives known in the art.

[0119] In some embodiments, the functional additives include at least one of a film-forming additive and a complexing additive.

[0120] Film-forming additives can form a protective layer at the interface of the electrode sheet, reducing the corrosion of the electrolyte; complexing additives can complex with the transition metals on the surface of the active material, improve the stability of the active material surface during the charge and discharge process, and reduce the dissolution of transition metals caused by surface structure degradation.

[0121] In some embodiments, the above-mentioned film-forming additives include at least one of sulfate film-forming additives, sulfite film-forming additives, sultone film-forming additives, disulfonic acid film-forming additives, aromatic film-forming additives, isocyanate film-forming additives, phosphite film-forming additives, phosphate film-forming additives and borate film-forming additives.

[0122] In some embodiments, the film-forming additive includes at least one of 1,3-propane sultone, vinyl sulfate, propylene sulfate, and vinyl sulfite.

[0123] In some embodiments, the complexing additive includes at least one of a nitrile complexing additive, a crown ether complexing additive, and an oxime complexing additive.

[0124] In some embodiments, the complexing additive includes 1,2,3-tris(2-cyanato)propane.

[0125] In some embodiments, the electrolyte salt may be selected from commonly used electrolyte salts in the art, such as lithium ion electrolyte salts, sodium ion electrolyte salts, and potassium ion electrolyte salts.

[0126] In some embodiments, the electrolyte salt includes a lithium ion electrolyte salt.

[0127] As an example, the lithium ion electrolyte salt includes, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0128] In some embodiments, 1 g of the functional resin layer contains 0.2 mg to 5 mg of cations.

[0129] In the above "0.2mg~5mg", the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and the following point values: 0.2mg, 0.5mg, 1mg, 1.2mg, 2mg, 3mg, 4mg, 5mg; or a range consisting of any two values, for example: 1mg~5mg, 2mg~5mg, 3mg~5mg, 2mg~3mg.

[0130] In some embodiments, the thickness of the functional resin layer is 1 μm to 50 μm.

[0131] In some embodiments, the thickness of the functional resin layer is 2 μm to 30 μm.

[0132] In some embodiments, the thickness of the functional resin layer is 5 μm to 20 μm.

[0133] In the above "1μm~50μm", the values ​​include the minimum and maximum values ​​of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and the following point values: 1μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm; or a range consisting of any two values, for example: 1μm~50μm, 5μm~50μm, 10μm~50μm, 20μm~50μm, 1μm~30μm, 5μm~30μm, 10μm~30μm, 15μm~30μm, 1μm~20μm, 5μm~20μm, 10μm~20μm, 15μm~20μm.

[0134] The thickness of the functional resin layer is further regulated to improve ion transport while maintaining the good transition metal ion capture efficiency of the composite isolation membrane, thereby further improving the cycle performance of the secondary battery.

[0135] The material of the base film in the present application can be any porous structure material known in the art with good chemical stability and mechanical stability.

[0136] In some embodiments, the material of the base film includes at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0137] Optionally, the base film has a thickness of 2 μm to 15 μm.

[0138] In some embodiments, the secondary battery further includes a positive electrode sheet and a negative electrode sheet, and a composite isolation membrane is arranged between the positive electrode sheet and the negative electrode sheet. In the composite isolation membrane, a functional resin layer is provided on at least one surface of the base membrane closer to the positive electrode sheet.

[0139] During the charge and discharge process of a secondary battery, the negative electrode is at a lower potential than the positive electrode. At this low potential, transition metal ions captured by the iminodiacetate groups are easily attracted by the electric field, causing a small amount of desorption and deposition at the negative electrode, reducing the composite separator's adsorption efficiency for transition metal ions. Therefore, a functional resin layer is provided on at least one side of the base film closer to the positive electrode to enhance the composite separator's adsorption efficiency for transition metal ions.

[0140] It can be understood that the base film has two opposite surfaces in its thickness direction, and at least the surface closer to the positive electrode sheet is provided with a functional resin layer.

[0141] The positive electrode sheet and the negative electrode sheet in the present application can adopt various commonly used positive electrode sheet and negative electrode sheet systems in the art. The polarity of the positive electrode sheet and the negative electrode sheet are illustrated below.

[0142] Positive electrode sheet: The positive electrode sheet includes a current collector and a positive electrode active layer loaded on the surface of the current collector.

[0143] The components of the positive electrode active layer include a positive electrode active material. The positive electrode active material can be selected from commonly used positive electrode active materials in the art, including but not limited to: positive electrode active materials for lithium ion batteries, positive electrode active materials for sodium ion batteries, and positive electrode active materials for potassium ion batteries.

[0144] The positive electrode active material of a lithium ion battery, the positive electrode active material of a sodium ion battery, and the positive electrode active material of a potassium ion battery are hereinafter referred to as lithium ion active material, sodium ion active material, and potassium ion active material, respectively.

[0145] Further, as an example, the lithium ion active material may include at least one of the following materials: lithium phosphates containing olivine structure, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries can also be used. These positive electrode active materials can be used alone or in combination of two or more. Examples of lithium transition metal oxides may include but are not limited to lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15Al 0.05 O2) and at least one of its modified compounds, etc.

[0146] Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4, abbreviated as LFP), lithium manganese phosphate (such as LiMnPO4), and lithium manganese iron phosphate. In any embodiment of the present application, the molecular formula of the lithium ion active material is: LiFe x Mn (1-x) PO4, x is any number from 0 to 1.

[0147] It can be understood that when x is 0, LiFe x Mn (1-x) PO4 is LiMnPO4 lithium manganese phosphate. When x is 1, LiFe x Mn (1-x) PO4 is LiFePO4 lithium iron phosphate (LFP).

[0148] It should be noted that the lithium content in the positive electrode material exemplified above refers to its content when it is not in use. During the use of the battery, it will be repeatedly used as a battery, and the Li in the positive electrode active material will change during the charge and discharge process. That is, the molar subscript of Li in the positive electrode active material in the battery product will not always remain at 1, but will change; further, the range of change can be (0 to 1.2).

[0149] For example, LiFe x Mn (1-x) PO4 can be further expressed as Li y Fe x Mn (1-x) PO4, y is 0~1.1.

[0150] For example, for the ternary material Li y (Ni a Co b Mn c ) 1-d M d O 2-x A x , y is 0.2~1.2, a+b+c=1, 0≤d≤1, 0≤x<2; M is one or more of Zr, Sr, B, Ti, Mg, Sn and Al, and A is one or more of S, N, F, Cl, Br and I.

[0151] The battery is accompanied by Li intercalation and deintercalation and consumption during the charge and discharge process. The molar content of Li varies when the battery is discharged to different states. The above definition of y includes the molar content of Li under different charge and discharge states of the battery. Furthermore, the battery voltage is usually between 2-5V.

[0152] As an example, the sodium ion active material may include at least one of the following materials: a sodium transition metal oxide, a polyanionic compound, and a Prussian blue compound. However, the present application is not limited to these materials, and other conventionally known materials that can be used as sodium ion battery positive electrode active materials may also be used.

[0153] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal includes at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Sodium transition metal oxide is, for example, Na x MO2, wherein M includes at least one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0154] As an optional technical solution of the present application, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. Transition metals include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y includes at least one of P, S, and Si; n represents (YO4) n- valence.

[0155] Polyanionic compounds can also be sodium ions, transition metal ions, tetrahedral (YO4) n- A class of compounds containing anion units and halogen anions. The transition metal includes at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y includes at least one of P, S, and Si, and n represents (YO4) n- valence state; the halogen may be at least one of F, Cl and Br.

[0156] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedron unit (ZO y ) m+ and an optional halogen anion. Y includes at least one of P, S and Si, and n represents (YO4) n- valence state; Z represents a transition metal, including at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, m represents (ZO y ) m+ valence state; the halogen may be at least one of F, Cl and Br.

[0157] Polyanionic compounds include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7)(NFPP), NaM1PO4F and Na3(VO y )2(PO4)2F (3-2y) At least one of .

[0158] M1 is at least one of V, Fe, Mn and Ni, and 0≤y≤1.

[0159] Prussian blue compounds can be sodium ions, transition metal ions and cyanide ions (CN - ). The transition metal includes at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Prussian blue compounds are, for example, Na a M2 b M3 c (CN)6, wherein M2 and M3 are each independently selected from at least one of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0160] In any embodiment of the present application, in the positive electrode active layer, the mass proportion of the positive electrode active material is 70% to 99.8%.

[0161] In any embodiment of the present application, the components of the positive electrode active layer further include a conductive agent and a binder.

[0162] The conductive agent may be any commonly used conductive agent in the art, including but not limited to at least one of graphite, carbon nanotubes, nanofibers, carbon black, and graphene. Specifically, the conductive agent may include at least one of conductive carbon black (super pll, SP), conductive graphite SFG-6, conductive graphite KS-6, acetylene black, branched superconducting carbon black Ketjen black (ECP), vapor grown carbon fiber (VGCF), carbon nanotubes (CNTs), graphene, and composite conductive agents thereof.

[0163] The binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, hydrogenated nitrile rubber, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS) and fluorine-containing acrylate resin.

[0164] In some embodiments, the conductive agent accounts for 1% to 20% by mass in the positive electrode active layer.

[0165] In some embodiments, in the positive electrode active layer, the binder accounts for 1% to 10% by mass.

[0166] In any embodiment of the present application, the current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material on a polymer substrate.

[0167] In some embodiments, the metal material is selected from any one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.

[0168] In some embodiments, the polymer material substrate includes at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0169] In any embodiment of the present application, the positive electrode sheet can be prepared by the following method: dispersing the above-mentioned components for preparing the positive electrode sheet in an organic solvent to form a positive electrode slurry; coating the positive electrode slurry on the current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0170] In some embodiments, the solid content of the positive electrode slurry is 40 wt % to 80 wt %, and the viscosity at 25° C. is adjusted to 5000 mPa·s to 25000 mPa·s.

[0171] In some embodiments, the organic solvent includes but is not limited to: N-methylpyrrolidone.

[0172] In some embodiments, the surface density of the positive electrode active material contained in the positive electrode sheet is 0.018 g / cm 2 ~0.05g / cm 2 .

[0173] Areal density of positive electrode active material = mass of positive electrode active material / area of ​​positive electrode sheet.

[0174] Negative electrode: The negative electrode may be any of the negative electrode systems commonly used in the art for secondary batteries. Examples of the negative electrode include lithium-ion secondary batteries and lithium metal secondary batteries, but are not limited to the following types.

[0175] In some embodiments, the secondary battery is a lithium metal secondary battery, and the negative electrode sheet can be a negative electrode sheet that can be used for a lithium metal battery and is well known in the art.

[0176] In some embodiments, the negative electrode sheet directly adopts a lithium-containing metal sheet.

[0177] In another embodiment, the negative electrode sheet includes a lithium-containing metal layer and a conductive layer stacked together.

[0178] Furthermore, the lithium-containing metal in the lithium-containing metal sheet and the lithium-containing metal layer can be lithium metal, or an alloy formed by lithium metal and other metal or non-metal elements.

[0179] Further, the other metals include at least one of tin (Sn), zinc (Zn), aluminum (Al), magnesium (Mg), silver (Ag), gold (Au), gallium (Ga), indium (In) and platinum (Pt); the non-metallic elements include at least one of boron (B), carbon (C) and silicon (Si).

[0180] In some embodiments, the conductive layer may be copper foil.

[0181] In any embodiment of the present application, the negative electrode sheet can be prepared by directly pressing a lithium-containing metal sheet to obtain the negative electrode sheet, or by stacking and pressing the lithium-containing metal layer and the conductive layer to obtain the negative electrode sheet.

[0182] In some embodiments, the secondary battery is a lithium-ion secondary battery, and the negative electrode sheet can be a negative electrode sheet that can be used for a lithium-ion secondary battery and is well known in the art.

[0183] In some embodiments, the negative electrode sheet includes a current collector and a negative electrode active layer supported on a surface of the current collector.

[0184] The components of the negative electrode active layer include a negative electrode active material.

[0185] The negative electrode active material may be any commonly used negative electrode active material in this application.

[0186] In any embodiment of the present application, the above-mentioned negative electrode active material includes at least one of mesocarbon microbeads, graphite, glassy carbon, carbon nanotubes, carbon-carbon composite materials, carbon fibers, hard carbon, soft carbon, silicon-based materials, tin-based materials, magnesium-based materials and iron-based materials.

[0187] Optionally, specific examples of the above-mentioned negative electrode active materials include, but are not limited to: at least one of mesophase carbon microbeads, natural graphite, artificial graphite, graphene, glassy carbon, carbon nanotubes, carbon fibers, hard carbon, soft carbon, iron oxide, tin oxide, silicon oxide, magnesium oxide, silicon-carbon composites, lithium metal and lithium metal alloys.

[0188] In any embodiment of the present application, the mass proportion of the negative electrode active material in the negative electrode active layer is 70% to 100%.

[0189] In any embodiment of the present application, the components of the negative electrode active layer further include a negative electrode conductive agent and a negative electrode binder.

[0190] In any embodiment of the present application, the above-mentioned negative electrode conductive agent can be a conductive material commonly used in the art, including but not limited to: at least one of graphite, carbon nanotubes, nanofibers, carbon black and graphene. Specifically, it can include at least one of conductive carbon black (super pll, referred to as SP), conductive graphite SFG-6, conductive graphite KS-6, acetylene black, branched superconducting carbon black Ketjen black (ECP), vapor grown carbon fiber (VGCF), carbon nanotubes (CNTs) and graphene and composite conductive agents thereof.

[0191] In some embodiments, based on the total weight of the negative electrode active layer, the weight ratio of the negative electrode conductive agent in the negative electrode active layer is 0 to 20 wt %.

[0192] The negative electrode binder may be a binder commonly used in the art, and may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0193] In some embodiments, based on the total weight of the negative electrode active layer, the weight ratio of the negative electrode binder in the negative electrode active layer is 0 to 30 wt %.

[0194] In any embodiment of the present application, the negative electrode active layer may further optionally include other additives, such as a thickener, such as sodium carboxymethyl cellulose (CMC-Na), etc. Based on the total weight of the negative electrode active layer, the weight ratio of the other additives in the negative electrode active layer is 0 to 15 wt%.

[0195] In any embodiment of the present application, the current collector in the negative electrode sheet may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil.

[0196] The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material on a polymer substrate.

[0197] In some embodiments, the metal material is selected from any one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.

[0198] In some embodiments, the polymer material substrate includes at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0199] In any embodiment of the present application, the negative electrode sheet can be prepared by the following method: the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0200] In some embodiments, the solvent includes but is not limited to water.

[0201] In some embodiments, the solid content of the negative electrode slurry is 30 wt % to 70 wt %, and the viscosity at 25° C. is adjusted to 2000 mPa·s to 10000 mPa·s.

[0202] In some embodiments, the surface density of the negative electrode active material contained in the negative electrode sheet is 0.005 g / cm 2 ~0.03g / cm 2 .

[0203] The area density of the negative electrode active material = the mass of the negative electrode active material / the area of ​​the negative electrode sheet.

[0204] The secondary battery of the present application may be in a cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 4 of a secondary battery with a square structure as an example.

[0205] In some embodiments, referring to FIG2 , the housing may include a shell 41 and a cover 43. Shell 41 may include a bottom plate and side plates connected to the bottom plate, with the bottom plate and side plates enclosing a receiving cavity. Shell 41 may have an opening communicating with the receiving cavity, and cover 43 may be positioned over the opening to seal the receiving cavity.

[0206] The positive electrode sheet, negative electrode sheet, and separator can be wound or laminated to form an electrode assembly 42. The electrode assembly 42 is enclosed in a housing. Electrolyte is infiltrated into the electrode assembly 42. The number of electrode assemblies 42 included in a battery cell 4 can be one or more, and can be adjusted based on demand.

[0207] The secondary battery includes one or more battery cells 4 .

[0208] The secondary battery can be a battery module or a battery pack; the battery module or battery pack includes at least one battery cell. The number of battery cells 4 included in the battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0209] Figures 3 and 4 illustrate an example battery pack 1. Battery pack 1 includes a battery case and one or more batteries 4 disposed within the case. The battery case comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for the battery cells 4.

[0210] The multiple batteries 4 can be arranged in the battery box in any manner.

[0211] The present application also provides an electrical device, which includes the above-mentioned secondary battery.

[0212] Furthermore, in the above-mentioned electrical device, the secondary battery may exist in the form of a battery cell, or may be further assembled into a battery pack.

[0213] The above-mentioned battery or the battery pack assembled therefrom can be used as a power source for an electrical device, or as an energy storage unit for an electrical device.

[0214] The above-mentioned electrical devices may be, but are not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc.

[0215] In some embodiments, the mobile device may be a mobile phone or a laptop computer, etc.

[0216] In some embodiments, electric vehicles include, but are not limited to, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, and the like.

[0217] Figure 5 shows an example of an electric device 5. The electric device 5 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device 5's requirements for high power and high energy density of the secondary battery, a battery pack can be used.

[0218] As another example, the power-consuming device may be a mobile phone, a tablet computer, a laptop computer, etc. Such a device is usually required to be light and thin, and may use a battery as a power source.

[0219] The present application will be described below in conjunction with specific embodiments, but the present application is not limited to the following embodiments. It should be understood that the attached claims summarize the scope of the present application. Under the guidance of the concept of the present application, those skilled in the art should realize that certain changes made to the various embodiments of the present application will be covered by the spirit and scope of the claims of the present application.

[0220] The following are specific examples.

[0221] Example 1

[0222] (1) Preparation of composite isolation:

[0223] S1, using Na + Type chelating resin (model CH-90) was used as the functional polymer.

[0224] Laser particle size analysis of functional polymers was performed using a Microtrac MRB S3500 series instrument. Samples were measured according to GB / T19077-2016 / ISO13320:2009. The specific testing procedure was as follows: 2 g of functional polymer was added to 20 mL of deionized water and ultrasonicated for 5 minutes to ensure complete dispersion of the sample. The dispersion was then placed in a sample tank and tested. The particle size-volume cumulative distribution curve was obtained, and the particle size corresponding to 50% of the volume distribution was defined as Dv50.

[0225] Functional polymers can be tested using infrared spectroscopy to determine the iminodiacetate groups in the main chain structure based on characteristic peaks. The specific infrared spectrometer used is: Bruker ALPHA, with a wavelength range of 400 cm -1 ~4000cm -1 .

[0226] S2. Functional polymer particles (Dv50=500 nm) and binder polyvinylidene fluoride are mixed in a mass ratio of 9:1, and then N-methylpyrrolidone is added, stirred, and dispersed to prepare a functional resin slurry.

[0227] The functional resin slurry is coated on a PE base film with a thickness of 8 μm, coated on one side, and the flow rate and coating speed of the slurry are controlled to make the coating thickness reach a predetermined thickness. After the coating is completed, it is dried to form a functional resin layer, and then cut to obtain a composite isolation film.

[0228] Use a micrometer to measure the thickness of the functional resin layer in the composite isolation film. The steps are as follows:

[0229] First, calibrate the micrometer, then place the composite isolation membrane between the double anvils, gently rotate the sleeve until a sound is heard, read and record the thickness, and subtract the thickness of the base membrane from the thickness of the composite isolation membrane to obtain the thickness of the functional resin layer, recorded as H. See Table 1 for details.

[0230] Test the cationic content (Li + 、Na + and K + ) quality, the specific tests are as follows:

[0231] At room temperature of 25° C., the functional resin layer is soaked in a hydrochloric acid aqueous solution with a mass concentration of 5% wt for 24 hours, wherein the functional resin layer and the hydrochloric acid solution are mixed in a mass ratio of 1:3. After soaking, the clear liquid is filtered and the concentration of the cations therein is detected by inductively coupled plasma-atomic emission spectrometry. The mass of the cations contained in the unit mass (1 g) of the functional resin layer can be converted and recorded as Y1.

[0232] (2) Preparation of electrolyte

[0233] S1: In an argon-filled glove box (water <10ppm, oxygen <10ppm), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC) and a mixed solvent were uniformly mixed in a mass ratio of 10:5:85, and then 8wt% of the total mass of the electrolyte was added as the solvent fluoroethylene carbonate (FEC), and then 2wt% of the additive 1,2,3-tris(2-cyano)propane and 2wt% of the additive 1,3-propane sultone were added as the total mass of the electrolyte, and finally lithium hexafluorophosphate was slowly added until an electrolyte with a molar concentration of lithium hexafluorophosphate of 1 mol / L was obtained.

[0234] Among them, the solvents of the electrolyte include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC) and fluoroethylene carbonate (FEC). Based on the total mass of the solvent, the mass proportion of cyclic carbonates (ethylene carbonate, propylene carbonate and fluoroethylene carbonate) is recorded as Y2.

[0235] The electrolyte was stored at 25° C. for 7 days to prepare a secondary battery.

[0236] S2: The conductivity of the electrolyte was tested according to the industry standard HG / T4067-2015 "Lithium Hexafluorophosphate Electrolyte" on page 5. The test temperature was 25°C.

[0237] S3: Test the content of hydrofluoric acid in the electrolyte, recorded as Y3.

[0238] Hydrofluoric acid in the electrolyte can be measured using instruments and methods known in the art. For example, refer to the national standard GB / T19282-2014, "Analysis Method for Lithium Hexafluorophosphate Products," pages 7-8, or the industry standard SJT 11723-2018, "Electrolytes for Lithium-ion Batteries," pages 3-5. The specific test steps are as follows:

[0239] Weigh about 20g of the electrolyte sample to be tested using the reduction method, accurate to 0.01g; quickly pour the sample into 100mL of ice-water mixture [50g ice cubes (d maxTo a beaker containing 10 mL of ice water (temperature ≤ 4°C), add 10 drops of bromothymol blue indicator solution and rapidly titrate with sodium hydroxide standard titration solution until the solution turns blue. This is the end point. There should still be ice in the solution at the end point.

[0240] The analysis process should be completed within 20 seconds. At the same time, a blank test should be carried out. Except for the absence of sample, the blank test solution contains the same type and amount of test solution as the test solution.

[0241] The free acid content in the electrolyte is generally measured as the mass fraction of hydrofluoric acid, and the value is expressed in mg / kg.

[0242] The content of hydrofluoric acid Y3 can be calculated by the following formula: Y3 = (V-V0) × c × M / (m × 10 -3 ),

[0243] Wherein, V is the volume of sodium hydroxide standard titrant consumed in titrating the test solution, in milliliters (mL); V0 is the volume of sodium hydroxide standard titrant consumed in titrating the blank test solution, in milliliters (mL); c is the concentration of sodium hydroxide standard titrant, in moles per liter (mol / L);

[0244] M is the molar mass of hydrofluoric acid in grams per mole (g / mol) (M=20.01); m is the mass of the sample in grams (g).

[0245] Calculate according to the formula and take the arithmetic mean of the parallel measurement results as the measurement result. The ratio of the absolute difference between the two parallel measurement results and the arithmetic mean shall not exceed 20%.

[0246] (3) Preparation of negative electrode sheet

[0247] The negative electrode active material (artificial graphite), the conductive agent (conductive carbon black), the binder (styrene-butadiene rubber (SBR)) and the thickener (sodium carboxymethyl cellulose) were mixed in a mass ratio of 96:1:2:1, deionized water was added, stirred, and dispersed to form a negative electrode slurry.

[0248] The negative electrode slurry is coated on the Cu foil. After both sides are completed, it is dried to form the negative electrode active layer, and then cold pressed, cut and sliced ​​to obtain the negative electrode sheet. The coating weight of the negative electrode active layer is 0.12g / 1540.25mm 2 The coating compaction density is 1.7g / cm 3 .

[0249] (4) Preparation of positive electrode

[0250] The positive electrode active material (LiCoO2), the conductive agent (conductive carbon black), and the binder (polyvinylidene fluoride) are mixed in a mass ratio of 97:1:2, and then N-methylpyrrolidone is added and stirred to disperse into a positive electrode slurry.

[0251] The positive electrode slurry is coated on the aluminum foil. After coating on both sides, it is dried to form the positive electrode active layer, and then cold pressed and cut to prepare the positive electrode sheet. The coating weight of the positive electrode active layer is 0.3g / 1540.25mm 2 The coating compaction density is 4.2g / cm 3 .

[0252] (5) Assembly of secondary battery: The positive electrode sheet, composite separator, and negative electrode sheet are stacked in order, with the functional resin layer on the composite separator facing the positive electrode sheet, to obtain an electrode assembly.

[0253] The electrode assembly is placed in an outer package, and the above electrolyte is injected with an injection coefficient of 2.5g / mAh. The steps of packaging, injection, formation, and exhaust are then carried out to obtain a lithium-ion secondary battery.

[0254] (6) Performance test of secondary batteries:

[0255] 1. Battery cycle test at 25℃

[0256] The secondary batteries prepared in the examples and comparative examples were charged and discharged for the first time at 25°C, and the process was as follows: after standing at 25°C for 30 minutes, the secondary battery was charged to 4.45V at a constant current of 0.33C, and then charged at a constant voltage until the current was ≤0.05C; then, the battery was discharged to 2.5V at a constant current of 0.33C, and the discharge capacity C1 of the first cycle was recorded; subsequently, the battery was continuously charged and discharged at 0.33C1 / 0.33C1 in a voltage range of 2.5V to 4.45V, and the discharge capacity after 1000 cycles was recorded as C1000, and the capacity retention rate P1000 = C1000 / C1×100%.

[0257] Please see Table 1 for specific results.

[0258] 2. Battery 45℃ storage capacity retention test

[0259] At 25°C, the batteries of the above examples and comparative examples were charged at a constant current of 0.33C to a voltage of 4.45V, then charged at a constant voltage of 4.45V to a current of ≤0.05C. The batteries were discharged at a constant current of 0.33C to a voltage of 2.5V, and the actual discharge capacity of the batteries was recorded as C0. At 25°C, the batteries were further charged at a constant current of 0.33C0 to a voltage of 4.45V, and then charged at a constant voltage of 4.45V to a current of ≤0.05C0, at which point the batteries were fully charged. The fully charged batteries were stored in a constant temperature chamber at 45°C for 180 days, after which the batteries were removed for capacity testing.

[0260] The capacity retention rate of the battery after 180 days of storage at 45°C = (discharge capacity of the battery after 180 days of storage / actual discharge capacity of the battery C0) × 100%. The capacity retention rate P180 is the capacity retention rate after 180 days of storage. For details, please see Table 1.

[0261] 3. Transition metal Co deposition test

[0262] The batteries from each of the above examples and comparative examples were discharged at a constant current of 0.33C to 2.5V, then transferred to a glove box for disassembly, retaining the negative electrode sheet. The negative electrode sheet was soaked in methyl formate at a mass ratio of 10:1, with the methyl formate replaced every two hours for two changes. After cleaning, the negative electrode sheet was transferred to a vacuum drying oven at 80°C for 24 hours. Approximately 2g of the negative electrode sheet was digested with concentrated nitric acid to form a solution. The mass content of transition metal Co in the solution was measured using an inductively coupled plasma optical emission spectrometer (ICP-OES) (model iCAP 7400), and the amount of transition metal Co deposited on the entire negative electrode sheet was converted.

[0263] Examples 2-3

[0264] Examples 2 to 3 are basically the same as Example 1, except that: in step (1) the preparation of the composite isolation, the type of functional polymer is different from that in Example 1, wherein Example 2 uses Li + Type porous resin; Example 3 uses K + Type porous resin.

[0265] Among them, Example 2 uses Li + The porous resin is made by using Na + The chelating resin (model CH-90) was immersed in a 10 wt% LiOH aqueous solution, wherein Na + The mass ratio of the chelating resin to the LiOH aqueous solution is 1:10.

[0266] Example 2 uses K + The porous resin is made by using Na +The chelating resin (model CH-90) was immersed in a 10 wt% KOH aqueous solution, wherein Na + The mass ratio of the chelating resin to the KOH aqueous solution is 1:10.

[0267] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0268] Examples 4 to 7

[0269] Examples 4 to 7 are substantially the same as Example 1, except that the storage time of the electrolyte is different from that of Example 1. The storage time of the electrolyte in Examples 4 to 7 is 0 days, 15 days, 30 days, and 60 days, respectively, so that the content of hydrofluoric acid in the electrolyte is different from that of the example. See Table 1 for details.

[0270] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0271] Example 8

[0272] Example 8 is basically the same as Example 1, except that: in step (1) the preparation of the composite isolation, the type of functional polymer is different from that in Example 1, wherein Example 8 uses Na + Type polyacrylic acid porous resin.

[0273] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0274] Examples 9 to 13

[0275] Examples 9 to 13 are basically the same as Example 1, except that in step (1) the preparation of the composite isolation, the particle size Dv50 of the functional polymer is different from that in Example 1. Please see Table 1 for details.

[0276] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0277] Examples 14 to 19

[0278] Examples 14 to 19 are basically the same as Example 1, except that in step (1) of preparing the composite isolation, the thickness H of the functional resin layer is different from that in Example 1. For details, see Table 1.

[0279] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0280] Examples 20-21

[0281] Examples 20 to 21 are substantially the same as Example 1, except that in the preparation of the electrolyte in step (2), the concentration of lithium hexafluorophosphate is different from that in Example 1. The concentration of lithium hexafluorophosphate in Example 20 is 0.5 mol / L, and the concentration of lithium hexafluorophosphate in Example 21 is 2 mol / L.

[0282] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0283] Examples 22 to 25

[0284] Examples 22 to 25 are basically the same as Example 1, except that in step (2) of preparing the electrolyte, the ratio of the solvent is different from that in Example 1, so that the value of Y2 is different from that in Example 1. Please see Table 1 for details.

[0285] Among them, in Example 22, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC) and are uniformly mixed in a mass ratio of 15:10:75 to obtain a mixed solvent, and the mass proportion of the solvent fluoroethylene carbonate (FEC) in the electrolyte is 8%.

[0286] In Example 23, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC) and propylene carbonate (PC) are uniformly mixed in a mass ratio of 5:0:95 to obtain a mixed solvent, and the mass proportion of the solvent fluoroethylene carbonate (FEC) in the electrolyte is 5%.

[0287] In Example 24, an equal mass of ethyl methyl carbonate (EMC) is used to replace the mixed solvent of ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in Example 1, and the mass proportion of the solvent fluoroethylene carbonate (FEC) in the electrolyte is 5%.

[0288] In Example 25, ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) are uniformly mixed in a mass ratio of 25:15:60 to obtain a mixed solvent, and the mass proportion of the solvent fluoroethylene carbonate (FEC) in the electrolyte is 8%.

[0289] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0290] Example 26

[0291] Example 26 is basically the same as Example 1, except that during the assembly step of the secondary battery, the functional resin layer on the composite isolation membrane is placed facing the negative electrode sheet.

[0292] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0293] Comparative Example 1

[0294] Comparative Example 1 is basically the same as Example 1, except that in the assembly step of the secondary battery, a PE base film is directly used instead of the composite isolation film, and the thickness of the PE base film is the same as that of the composite isolation film in Example 1. Please see Table 1 for details.

[0295] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0296] Comparative Example 2

[0297] Comparative Example 2 is substantially the same as Example 1, except that in step (2) of preparing the electrolyte, the value of Y2 is different from that in Example 1. Specifically, ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) are uniformly mixed in a mass ratio of 30:20:50 to form a mixed solvent, and the mass proportion of the solvent fluoroethylene carbonate (FEC) in the electrolyte is 8%. See Table 1 for details.

[0298] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0299] The relevant parameters and performance results of each embodiment and comparative example are shown in Table 1. Here, the thickness of the functional resin layer is denoted as H; the mass of the cations contained in the functional resin layer per unit mass (1 g) is denoted as Y1 (mg / g); the mass percentage of the cyclic carbonate in the electrolyte, based on the total mass of the solvent, is denoted as Y2; and the hydrofluoric acid content in the electrolyte is denoted as Y3.

[0300] Table 1

[0301] Note: In Table 1, “ / ” means that the substance or parameter does not exist.

[0302] Analysis of the data in Table 1: By comparing the test results of Example 1 with those of Comparative Examples 1 to 2, it can be seen that the technical solution of the present application can achieve directional capture of transition metal ions while ensuring a good ion transmission rate, thereby effectively improving the cycle performance and storage stability of the secondary battery.

[0303] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0304] The above-described embodiments merely represent several implementation methods of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make a number of variations and improvements without departing from the concept of the present application, and these variations and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the patent for this invention shall be based on the appended claims, and the description and drawings may be used to interpret the content of the claims.

Claims

1. A secondary battery, wherein: The secondary battery comprises a composite separator and an electrolyte; The composite isolation film comprises a base film and a functional resin layer arranged on the surface of the base film, wherein the functional resin layer comprises a functional polymer, wherein the functional polymer contains an iminodiacetate group, and the cation of the iminodiacetate group comprises Li + 、Na + and K + At least one of; At 25° C., the conductivity of the electrolyte is greater than or equal to 5 mS / cm.

2. The secondary battery according to claim 1, wherein The iminodiacetate group is shown in formula (1): Among them, X + and Y + are independently selected from H + , Li + 、Na + , K + Any one of the above, and X + and Y + Different from H + ; * is the connection site.

3. The secondary battery according to any one of claims 1 to 2, wherein: The side chains of the functional polymer are grafted with the iminodiacetate groups.

4. The secondary battery according to any one of claims 1 to 3, wherein The volume distribution particle size Dv50 of the functional polymer is 100nm to 1200nm; Optionally, the volume distribution particle size Dv50 of the functional polymer is 100nm to 1000nm; Further optionally, the volume distribution particle size Dv50 of the functional polymer is 200nm to 600nm.

5. The secondary battery according to any one of claims 1 to 4, wherein The functional polymer satisfies at least one of the following conditions (1) to (3): (1) The raw materials for preparing the main chain of the functional polymer include at least one of acrylic monomers and styrene; (2) The functional polymer is a cross-linked polymer; (3) In the functional resin layer, the mass proportion of the functional polymer is 80% to 95%.

6. The secondary battery according to any one of claims 1 to 5, wherein The mass content of hydrofluoric acid in the electrolyte is less than or equal to 300 ppm.

7. The secondary battery according to any one of claims 1 to 6, wherein: The components of the electrolyte include an electrolyte salt and a solvent, the solvent includes a cyclic carbonate, and the mass proportion of the cyclic carbonate in the solvent is less than 50%; Optionally, the mass proportion of the cyclic carbonate in the solvent is 5% to 46%; Further optionally, the cyclic carbonate includes at least one of ethylene carbonate, vinylene carbonate, propylene carbonate, butylene carbonate and fluoroethylene carbonate.

8. The secondary battery according to claim 7, wherein: The electrolyte satisfies at least one of the following conditions (1) to (2): (1) The solvent also includes a chain ester solvent; Optionally, the chain ester solvent includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate and propyl propionate; (2) The concentration of the electrolyte salt is 0.5 mol / L to 2 mol / L.

9. The secondary battery according to any one of claims 1 to 8, wherein The components of the electrolyte also include functional additives; Optionally, the mass of the functional additive accounts for 2% to 15% of the total mass of the electrolyte.

10. The secondary battery according to claim 9, wherein The functional additive includes at least one of a film-forming additive and a complexing additive; Optionally, the film-forming additive includes at least one of a sulfate film-forming additive, a sulfite film-forming additive, a sultone film-forming additive, a disulfonic acid film-forming additive, an aromatic film-forming additive, an isocyanate film-forming additive, a phosphite film-forming additive, a phosphate film-forming additive, and a borate film-forming additive; Optionally, the complexing additive includes at least one of a nitrile complexing additive, a crown ether complexing additive and an oxime complexing additive.

11. The secondary battery according to any one of claims 1 to 10, wherein The functional resin layer satisfies at least one of the following conditions (1) to (2): (1) 1 g of the functional resin layer contains 0.2 mg to 5 mg of the cation; (2) The thickness of the functional resin layer is 1 μm to 50 μm; Optionally, the thickness of the functional resin layer is 2 μm to 30 μm; Further optionally, the thickness of the functional resin layer is 5 μm to 20 μm.

12. The secondary battery according to any one of claims 1 to 5 and 8 to 11, wherein The secondary battery further comprises a positive electrode sheet and a negative electrode sheet, the composite isolation membrane is arranged between the positive electrode sheet and the negative electrode sheet, and in the composite isolation membrane, at least the functional resin layer is arranged on the surface of the base membrane closer to the positive electrode sheet.

13. An electrical device, wherein: The electric device comprises the secondary battery according to any one of claims 1 to 12.

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