Secondary battery and electric device

Abstract

The invention relates to a secondary battery and a power utilization device. The secondary battery comprises a composite isolating membrane and an electrolyte, the composite isolating membrane 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, and cations of the iminodiacetate group comprise at least one of Li < + >, Na < + > and K < + >; at 25 DEG C, the conductivity of the electrolyte is greater than or equal to 5 mS / cm.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a secondary battery and an electrical device. Background Art

[0002] Secondary batteries such as lithium-ion batteries are increasingly widely used due to their clean and renewable characteristics. They have been widely used in many fields such as consumer electronics, electric vehicles and energy storage. Secondary batteries such as lithium-ion batteries mainly rely on the movement of ions between the positive and negative electrodes to work. There is a separator between the positive and negative electrodes. On the one hand, it isolates the positive and negative electrodes to prevent short circuits in the battery. On the other hand, it can be wetted by the electrolyte to form a channel for ion migration.

[0003] As the application scope of secondary batteries continues to expand, the performance requirements for secondary batteries are getting higher and higher, such as seeking higher energy density. Therefore, using high-voltage positive electrode materials to seek higher energy density has become a trend. However, when the battery is in service at high voltage, the structure of the positive electrode material tends to be unstable and the structure of the positive electrode material is prone to collapse, which directly leads to the dissolution of a large amount of transition metal ions. The dissolved transition metal ions may deposit on the anode or catalyze the decomposition of the negative electrode interface film and electrolyte components. At the same time, there is also the risk of dendrite growth, piercing the isolation membrane and causing the cell to fail, which greatly limits the improvement of the cycle performance and storage stability of the secondary battery.

[0004] Therefore, the traditional technology needs to be further improved. Summary of the invention

[0005] Based on this, it is necessary to provide a secondary battery and an electrical device to improve the cycle performance and storage stability of the secondary battery.

[0006] The present application is implemented through the following technical solutions.

[0007] In a first aspect of the present application, a secondary battery is provided, the secondary battery comprising a composite separator and an electrolyte;

[0008] 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;

[0009] At 25° C., the conductivity of the electrolyte is greater than or equal to 5 mS / cm.

[0010] 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 an iminodiacetate group that can directional capture transition metal ions, wherein the iminodiacetate group is fixed on the surface of the composite separator through the functional resin layer, and the Li contained in the iminodiacetate group + 、Na + , K + The cations will exchange with the transition metal ions, so that the transition metal ions in the electrolyte are fixed on the surface of the composite isolation membrane, reducing the probability of them being at the pole piece or dispersed in the electrolyte; on the other hand, in the process of ion exchange between the cations in the iminodiacetate group in the functional resin layer and the transition metal ions in the electrolyte, the iminodiacetate group is electronegative after dissociating the cations, which will repel the anions of the electrolyte salt in the electrolyte and attract active ions such as lithium ions, resulting in the inhibition of the transmission of anions and cations at the positive and negative electrodes during the charge and discharge process, and the increase of polarization. Therefore, by controlling the conductivity of the electrolyte at the same time, the dissociation ability of the solvent in the electrolyte to the electrolyte salt is enhanced, and the transmission of anions and cations in the electrolyte is promoted. In this way, the two aspects cooperate to achieve the 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.

[0011] In some embodiments, the iminodiacetate group is represented by formula (1):

[0012]

[0013] 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 + ;

[0014] * is the connection site.

[0015] In some embodiments, the branched chains of the functional polymer are grafted with the iminodiacetate groups.

[0016] By grafting iminodiacetate groups on the side chains, the iminodiacetate groups are introduced into the functional polymer, so that the iminodiacetate groups are chemically bonded to the polymer, so that the iminodiacetate groups are more stably fixed on the functional resin layer, reducing the probability of their dissociation and dispersion into the electrolyte.

[0017] In some embodiments, the volume distribution particle size Dv50 of the functional polymer is 100 nm to 1200 nm;

[0018] Optionally, the volume distribution particle size Dv50 of the functional polymer is 100nm to 1000nm;

[0019] Further optionally, the volume distribution particle size Dv50 of the functional polymer is 200nm to 600nm.

[0020] 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.

[0021] In some embodiments, the functional polymer satisfies at least one of the following conditions (1) to (3):

[0022] (1) The raw materials for preparing the main chain of the functional polymer include at least one of acrylic monomers and styrene;

[0023] 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 diaphragm and further improve the performance of the secondary battery.

[0024] (2) The functional polymer is a cross-linked polymer;

[0025] The cross-linked polymer has better mechanical strength and can further improve the stability of the composite isolation membrane.

[0026] (3) In the functional resin layer, the mass proportion of the functional polymer is 80% to 95%.

[0027] In some embodiments, the mass content of hydrofluoric acid in the electrolyte is less than or equal to 300 ppm.

[0028] Hydrofluoric acid itself is corrosive to a certain extent, which will have a negative impact on the performance of secondary batteries. At the same time, hydrofluoric acid dissociates into hydrogen ions in the electrolyte, and the hydrogen ions exchange with the iminodiacetate groups to form stable iminodiacetic acid groups, which are not conducive to the capture of transition metal ions. Therefore, the mass content of hydrofluoric acid in the electrolyte is further regulated to improve the capture efficiency of the composite isolation membrane for transition metal ions.

[0029] 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%;

[0030] Optionally, the mass proportion of the cyclic carbonate in the solvent is 5% to 46%;

[0031] On the one hand, the type of solvent of the electrolyte is adjusted. The cyclic carbonate has an excellent ability to promote the dissociation of the electrolyte salt, 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 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.

[0032] Further optionally, the cyclic carbonate includes at least one of ethylene carbonate, vinylene carbonate, propylene carbonate, butylene carbonate and fluoroethylene carbonate.

[0033] In some embodiments, the electrolyte satisfies at least one of the following conditions (1) to (2):

[0034] (1) The solvent also includes a chain ester solvent;

[0035] Chain ester solvents are helpful in reducing the viscosity of the electrolyte and further improving the ion conductivity of the electrolyte.

[0036] 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;

[0037] (2) The concentration of the electrolyte salt is 0.5 mol / L to 2 mol / L.

[0038] In some of these embodiments, the components of the electrolyte further include functional additives;

[0039] Optionally, the mass of the functional additive accounts for 2% to 15% of the total mass of the electrolyte.

[0040] In some embodiments, the functional additive includes at least one of a film-forming additive and a complexing additive;

[0041] 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;

[0042] Optionally, the complexing additive includes at least one of a nitrile complexing additive, a crown ether complexing additive and an oxime complexing additive.

[0043] Film-forming additives can form a protective layer at the interface of the electrode sheet to reduce 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.

[0044] In some embodiments, the functional resin layer satisfies at least one of the following conditions (1) to (2):

[0045] (1) 1 g of the functional resin layer contains 0.2 mg to 5 mg of the cation;

[0046] (2) The thickness of the functional resin layer is 1 μm to 50 μm;

[0047] Optionally, the thickness of the functional resin layer is 2 μm to 30 μm;

[0048] Further optionally, the thickness of the functional resin layer is 5 μm to 20 μm.

[0049] 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 one surface of the base membrane closer to the positive electrode sheet.

[0050] During the charge and discharge process of the secondary battery, the negative electrode is at a low potential relative to the positive electrode. Under the action of the low potential, the transition metal ions captured by the iminodiacetate group are easily attracted by the electric field, resulting in a small portion of desorption and deposition on the negative electrode, reducing the adsorption effect of the composite isolation membrane on the transition metal ions. Therefore, at least one side of the base membrane closer to the positive electrode is provided with a functional resin layer to improve the adsorption effect of the composite isolation membrane on the transition metal ions.

[0051] According to a second aspect of the present application, there is provided an electric device, wherein the electric device comprises the secondary battery according to the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0053] Figure 1 is a schematic diagram of one embodiment of a battery cell;

[0054] Figure 2 yes Figure 1 Exploded diagram of

[0055] Figure 3 is a schematic diagram of an embodiment of a battery pack;

[0056] Figure 4 yes Figure 3 Exploded diagram of

[0057] Figure 5 is a schematic diagram of an embodiment of an electrical device in which a battery is used as a power source.

[0058] Description of reference numerals:

[0059] 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

[0060] The following embodiments of the technical solution of the present application will be described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0061] In the description of the embodiments of the present application, “plurality” means two or more, unless otherwise clearly and specifically defined.

[0062] In the present application, "room temperature" generally refers to 4°C to 30°C, preferably 20±5°C.

[0063] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0064] As described in the background art, transition metal ions released from secondary batteries during charge and discharge seriously 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.

[0065] Chelating functional groups generally chelate transition metal ions by dissociating alkali metal cations to exchange ions with transition metal ions. However, research has found that in the process of chelating and capturing transition metal ions, the chelating functional groups dissociate cations and become electronegative, which will repel the anions of the electrolyte salt in the electrolyte while attracting active ions such as lithium ions, resulting in the inhibition of the transmission of anions and cations at the positive and negative electrodes during the charge and discharge process, increasing polarization, and in turn causing the performance of the secondary battery to deteriorate.

[0066] Therefore, one embodiment of the present application provides a secondary battery, which includes a composite isolation membrane and an electrolyte.

[0067] The composite isolation film comprises a base film and a functional resin layer disposed on the surface of the base film, wherein the functional resin layer comprises a functional polymer, wherein the functional polymer comprises an iminodiacetate group, wherein the cation of the iminodiacetate group comprises Li + 、Na + and K + At least one of .

[0068] At 25° C., the conductivity of the electrolyte is greater than or equal to 5 mS / cm.

[0069] 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 an iminodiacetate group that can directional capture transition metal ions, wherein the iminodiacetate group is fixed on the surface of the composite separator through the functional resin layer, and the Li contained in the iminodiacetate group + 、Na + , K +The cations will exchange with the transition metal ions, so that the transition metal ions in the electrolyte are fixed on the surface of the composite isolation membrane, reducing the probability of them being at the pole piece or dispersed in the electrolyte; on the other hand, in the process of ion exchange between the cations in the iminodiacetate group in the functional resin layer and the transition metal ions in the electrolyte, the iminodiacetate group is electronegative after dissociating the cations, which will repel the anions of the electrolyte salt in the electrolyte and attract active ions such as lithium ions, resulting in the inhibition of the transmission of anions and cations at the positive and negative electrodes during the charge and discharge process, and the increase of polarization. Therefore, by controlling the conductivity of the electrolyte at the same time, the dissociation ability of the solvent in the electrolyte to the electrolyte salt is enhanced, and the transmission of anions and cations in the electrolyte is promoted. In this way, the two aspects cooperate to achieve the 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.

[0070] In some embodiments, at 25° C., the conductivity of the electrolyte is 5 mS / cm to 9 mS / cm.

[0071] In some embodiments, the above-mentioned iminodiacetate group is represented by formula (1):

[0072]

[0073] 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 + ;

[0074] * is the connection site.

[0075] In some embodiments, the branched chains of the functional polymers 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 are chemically bonded to the polymer, so that the iminodiacetate groups are more stably fixed on the functional resin layer, reducing the probability of their dissociation and dispersion into the electrolyte.

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

[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 iminodiacetate 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 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: in the particle size-volume cumulative distribution curve, the particle size corresponding to 50% of the volume distribution 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 can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Ltd. in the United Kingdom.

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

[0084] Take an appropriate amount of the sample to be tested and add it to deionized water. The sample concentration should be 8% to 12% shading. 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 of the 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 diaphragm and further improve the performance of the secondary battery.

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

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

[0091]

[0092] Here, each R1 is independently selected from a chain alkyl group having 1 to 5 carbon atoms.

[0093] In some embodiments, each R1 is independently selected from a chain alkyl group having 1 to 3 carbon atoms.

[0094] In some embodiments, the acrylic monomer includes at least one of acrylic acid and methacrylic acid.

[0095] In some embodiments, the functional polymer is a cross-linked polymer.

[0096] The cross-linked polymer has better mechanical strength and can further improve the stability of the composite isolation membrane.

[0097] In some of the embodiments, in the functional resin layer, the weight percentage of the functional polymer is 80% to 95%.

[0098] In the above "80%~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%~95%, 83%~95%, 85%~95%, 90%~95%.

[0099] In some of the embodiments, the component of the functional resin layer includes a binder.

[0100] The binder can further improve the stability of the composite isolation membrane.

[0101] 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.

[0102] In some of the embodiments, in the functional resin layer, the binder accounts for 5% to 20% by mass.

[0103] In the above "5%~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%~20%, 10%~20%, 15%~20%, 5%~15%.

[0104] In some embodiments, the mass content of hydrofluoric acid in the electrolyte is less than or equal to 300 ppm.

[0105] Hydrofluoric acid itself is corrosive to a certain extent, which will have a negative impact on the performance of secondary batteries. At the same time, hydrofluoric acid dissociates into hydrogen ions in the electrolyte, and the hydrogen ions exchange with the iminodiacetate groups to form stable iminodiacetic acid groups, which are not conducive to the capture of transition metal ions. Therefore, the mass content of hydrofluoric acid in the electrolyte is further regulated to improve the capture efficiency of the composite isolation membrane for transition metal ions.

[0106] In some of the 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%.

[0107] In some embodiments, the mass percentage of the cyclic carbonate in the solvent is 5% to 46%.

[0108] 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.

[0109] 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%, 13%, 24%, 25 %, 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%-45%, 10%-45%, 25%-45%, 15%-40%, 20%-40%.

[0110] In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate, vinylene carbonate, propylene carbonate, butylene carbonate and fluoroethylene carbonate.

[0111] In some embodiments, the solvent further comprises a chain ester solvent.

[0112] Chain ester solvents are helpful in reducing the viscosity of the electrolyte and further improving the ion conductivity of the electrolyte.

[0113] 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.

[0114] In some embodiments, the mass proportion of the cyclic carbonate in the solvent is 55% to 95%.

[0115] In some of the embodiments, the concentration of the electrolyte salt is 0.5 mol / L to 2 mol / L.

[0116] In some of these embodiments, the components of the electrolyte further include functional additives;

[0117] Optionally, the mass of the functional additive accounts for 2% to 15% of the total mass of the electrolyte.

[0118] In the above "2%~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%~15%, 10%~15%, 2%~10%, 2%~5%.

[0119] The functional additives in the present application can be any electrolyte additive known in the art.

[0120] In some embodiments, the functional additives include at least one of film-forming additives and complexing additives.

[0121] Film-forming additives can form a protective layer at the interface of the electrode sheet to reduce 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.

[0122] In some of the 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.

[0123] In some embodiments, the film-forming additive includes at least one of 1,3-propane sultone, vinyl sulfate, propylene sulfate and vinyl sulfite.

[0124] In some of the embodiments, the complexing additive includes at least one of a nitrile complexing additive, a crown ether complexing additive, and an oxime complexing additive.

[0125] In some of these embodiments, the complexing additive includes 1,2,3-tris(2-cyanato)propane.

[0126] 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.

[0127] In some embodiments, the electrolyte salt includes a lithium ion electrolyte salt.

[0128] 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).

[0129] In some of the embodiments, 1 g of the functional resin layer contains 0.2 mg to 5 mg of cations.

[0130] 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.

[0131] In some embodiments, the thickness of the functional resin layer is 1 μm to 50 μm.

[0132] In some embodiments, the thickness of the functional resin layer is 2 μm to 30 μm.

[0133] In some embodiments, the thickness of the functional resin layer is 5 μm to 20 μm.

[0134] 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 embodiment and the following point values: 1μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm; or a range consisting of any two numerical 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.

[0135] The thickness of the functional resin layer is further regulated to improve ion transmission while maintaining good transition metal ion capture efficiency of the composite isolation membrane, thereby further improving the cycle performance of the secondary battery.

[0136] 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.

[0137] In some embodiments, the material of the base film includes at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0138] Optionally, the base film has a thickness of 2 μm to 15 μm.

[0139] In some embodiments, the secondary battery further comprises a positive electrode and a negative electrode, a composite isolation membrane is disposed between the positive electrode and the negative electrode, and in the composite isolation membrane, a functional resin layer is disposed on at least one surface of the base membrane closer to the positive electrode.

[0140] During the charge and discharge process of the secondary battery, the negative electrode is at a low potential relative to the positive electrode. Under the action of the low potential, the transition metal ions captured by the iminodiacetate group are easily attracted by the electric field, resulting in a small portion of desorption and deposition on the negative electrode, reducing the adsorption effect of the composite isolation membrane on the transition metal ions. Therefore, at least one side of the base membrane closer to the positive electrode is provided with a functional resin layer to improve the adsorption effect of the composite isolation membrane on the transition metal ions.

[0141] It can be understood that the base film has two opposite surfaces in its thickness direction, and at least the surface on the side closer to the positive electrode sheet is provided with a functional resin layer.

[0142] 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 as follows.

[0143] 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.

[0144] The components of the positive electrode active layer include positive electrode active materials. The positive electrode active materials can be selected from the positive electrode active materials commonly used 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.

[0145] 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.

[0146] 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. Among them, 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 its modified compounds, etc.

[0147] 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, referred to 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 can be any number from 0 to 1.

[0148] 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).

[0149] 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 charging and discharging 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).

[0150] 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.

[0151] 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.

[0152] The battery will be accompanied by Li deintercalation and consumption during the charge and discharge process. The molar content of Li is different 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; further, the battery voltage is usually between 2-5V.

[0153] As an example, the sodium ion active material may include at least one of the following materials: at least one of 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 positive electrode active materials for sodium ion batteries may also be used.

[0154] 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. The 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.

[0155] 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 state.

[0156] Polyanionic compounds can also be those with 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.

[0157] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedral unit (ZO y ) m+ and a class of compounds containing 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.

[0158] 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 .

[0159] M1 is at least one of V, Fe, Mn and Ni, and 0≤y≤1.

[0160] 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.

[0161] 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%.

[0162] In any embodiment of the present application, the components of the positive electrode active layer further include a conductive agent and a binder.

[0163] The conductive agent may be a conductive agent commonly used in the art, including but not limited to: at least one of graphite, carbon nanotubes, nanofibers, carbon black and graphene. Specifically, it may include at least one of conductive carbon black (super pll, referred to as SP), conductive graphite SFG-6, conductive graphite KS-6, acetylene black, superconducting carbon black Ketjen black (ECP) with a branched structure, vapor-grown carbon fiber (VGCF), carbon nanotubes (CNTs) and graphene and composite conductive agents thereof.

[0164] 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.

[0165] In some of the embodiments, in the positive electrode active layer, the mass proportion of the conductive agent is 1% to 20%.

[0166] In some of the embodiments, in the positive electrode active layer, the binder accounts for 1% to 10% by mass.

[0167] In any embodiment of the present application, the current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on a polymer material substrate.

[0168] 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.

[0169] In some of the embodiments, the polymer material substrate includes at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0170] 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.

[0171] In some of the 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.

[0172] In some embodiments, the organic solvent includes, but is not limited to, N-methylpyrrolidone.

[0173] 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 .

[0174] The surface density of the positive electrode active material = the mass of the positive electrode active material / the area of ​​the positive electrode sheet.

[0175] Negative electrode sheet: The negative electrode sheet may adopt the negative electrode sheet system of various types of secondary batteries commonly used in the art, and lithium-ion secondary batteries and lithium metal secondary batteries are used as examples below, but are not limited to the following types.

[0176] In some of the 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.

[0177] In some embodiments, the negative electrode sheet directly adopts a lithium-containing metal sheet.

[0178] In another embodiment, the negative electrode sheet includes a lithium-containing metal layer and a conductive layer stacked together.

[0179] Furthermore, the lithium-containing metal in the lithium-containing metal sheet and the lithium-containing metal layer may be lithium metal, or an alloy formed by lithium metal and other metal or non-metal elements.

[0180] 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).

[0181] In some of these embodiments, the conductive layer may be a copper foil.

[0182] In any embodiment of the present application, the negative electrode sheet can be prepared in the following manner: directly pressing a lithium-containing metal sheet to obtain the negative electrode sheet, or stacking and pressing the lithium-containing metal layer and the conductive layer to obtain the negative electrode sheet.

[0183] In some of the embodiments, the secondary battery is a lithium-ion secondary battery, and the negative electrode sheet can be a negative electrode sheet known in the art that can be used for a lithium-ion secondary battery.

[0184] 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.

[0185] The components of the negative electrode active layer include a negative electrode active material.

[0186] The negative electrode active material mentioned above can adopt the commonly used negative electrode active material in this application.

[0187] In any embodiment of the present application, the above-mentioned negative electrode active material includes at least one of mesophase carbon 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.

[0188] 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.

[0189] In any embodiment of the present application, the mass proportion of the above-mentioned negative electrode active material in the negative electrode active layer is 70% to 100%.

[0190] 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.

[0191] 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, superconducting carbon black Ketjen black (ECP) with a branched structure, vapor-grown carbon fiber (VGCF), carbon nanotubes (CNTs) and graphene and composite conductive agents thereof.

[0192] 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 0-20 wt %.

[0193] The above-mentioned negative electrode binder can adopt the 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).

[0194] 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 0-30 wt %.

[0195] In any embodiment of the present application, the negative electrode active layer may further include other additives, such as thickeners, such as sodium carboxymethyl cellulose (CMC-Na), etc. Based on the total weight of the negative electrode active layer, the weight ratio of other additives in the negative electrode active layer is 0-15wt%.

[0196] 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.

[0197] The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material on a polymer material substrate.

[0198] 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.

[0199] In some of the embodiments, the polymer material substrate includes at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0200] In any embodiment of the present application, the negative electrode sheet can be prepared in the following manner: 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 collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0201] In some embodiments, the solvent includes but is not limited to water.

[0202] In some of the 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.

[0203] 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 .

[0204] The surface density of the negative electrode active material = the mass of the negative electrode active material / the area of ​​the negative electrode sheet.

[0205] The shape of the secondary battery of the present application can be cylindrical, square or any other shape. For example, Figure 1 The battery cell 4 of the secondary battery is an example of a square structure.

[0206] In some embodiments, reference Figure 2 The housing may include a shell 41 and a cover plate 43. The shell 41 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 41 has an opening connected to the receiving cavity, and the cover plate 43 can be covered on the opening to close the receiving cavity.

[0207] The positive electrode sheet, the negative electrode sheet and the separator can be wound or laminated to form an electrode assembly 42. The electrode assembly 42 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 42. The number of electrode assemblies 42 contained in the battery cell 4 can be one or more, which can be adjusted according to needs.

[0208] The secondary battery includes one or more battery cells 4 .

[0209] The secondary battery may 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 may be one or more, and those skilled in the art may select a suitable number according to the application and capacity of the battery module.

[0210] Figure 3 and Figure 4The battery pack 1 is used as an example. The battery pack 1 includes a battery box and one or more batteries 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for placing the battery cells 4.

[0211] The multiple batteries 4 can be arranged in the battery box in any manner.

[0212] The present application also provides an electrical device, which includes the secondary battery mentioned above.

[0213] 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.

[0214] 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.

[0215] The above-mentioned electrical devices may be, but are not limited to, mobile equipment, electric vehicles, electric trains, ships and satellites, energy storage systems, etc.

[0216] In some of these embodiments, the mobile device may be a mobile phone or a laptop computer, etc.

[0217] In some of the embodiments, the electric vehicle includes, but is not limited to, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.

[0218] Figure 5 The power consumption device 5 is taken as an example. The power consumption device 5 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device 5's requirements for high power and high energy density of the secondary battery, a battery pack may be used.

[0219] As another example, the power-consuming device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a battery may be used as a power source.

[0220] The present invention will be described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments. It should be understood that the attached claims summarize the scope of the present invention. Under the guidance of the concept of the present invention, those skilled in the art should realize that certain changes made to the various embodiments of the present invention will be covered by the spirit and scope of the claims of the present invention.

[0221] The following are specific embodiments.

[0222] Example 1

[0223] (1) Preparation of composite isolation:

[0224] S1, using Na + Type chelating resin (model CH-90) was used as the functional polymer.

[0225] Microtrac MRB S3500 was used to perform laser particle size analysis on the functional polymers. The samples were measured according to GB / T19077-2016 / ISO13320:2009 standard. The specific test process was as follows: 2 g of functional polymer was added with 20 mL of deionized water and ultrasonicated for 5 min to ensure that the sample was completely dispersed. The dispersion was then placed in a sample tank for testing to obtain the particle size-volume cumulative distribution curve. The particle size corresponding to 50% of the volume distribution was Dv50.

[0226] Infrared spectroscopy can be used to test functional polymers, and the iminodiacetate groups in the main chain structure can be determined based on the characteristic peaks. The specific infrared spectrometer used is: Bruker ALPHA, with a wavelength range of 400cm -1 ~4000cm -1 .

[0227] 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.

[0228] The functional resin slurry is coated on a PE base film with a thickness of 8 μm, and is coated on one side. The flow rate and coating speed of the slurry are controlled to make the coating thickness reach a predetermined thickness. After coating, it is dried to form a functional resin layer, and then cut to obtain a composite isolation film.

[0229] Use a micrometer to test the thickness of the functional resin layer in the composite isolation film. The steps are as follows:

[0230] 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. For details, please see Table 1.

[0231] Test the cationic content (Li + 、Na + and K + ) quality, the specific tests are as follows:

[0232] At room temperature 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 cations therein is detected by inductively coupled plasma-atomic emission spectroscopy. The mass of cations contained in the unit mass (1g) of the functional resin layer can be converted and recorded as Y1.

[0233] (2) Preparation of electrolyte

[0234] S1: In a glove box filled with argon (water content <10ppm, oxygen content <10ppm), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC) and a mixed solvent are uniformly mixed in a mass ratio of 10:5:85, and then 8wt% of the solvent fluoroethylene carbonate (FEC) is added to the total mass of the electrolyte, and then 2wt% of the additive 1,2,3-tri(2-cyano)propane and 2wt% of the additive 1,3-propane sultone are added to the total mass of the electrolyte, and finally lithium hexafluorophosphate is slowly added until an electrolyte with a molar concentration of lithium hexafluorophosphate of 1 mol / L is obtained.

[0235] 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.

[0236] The electrolyte was stored at 25° C. for 7 days to prepare a secondary battery.

[0237] S2: The conductivity of the electrolyte was tested according to the content on page 5 of the industry standard HG / T4067-2015 "Lithium Hexafluorophosphate Electrolyte" at a test temperature of 25°C.

[0238] S3: Test the content of hydrofluoric acid in the electrolyte, recorded as Y3.

[0239] The hydrofluoric acid in the electrolyte can be determined using instruments and methods known in the art. For example, you can refer to the national standard GB / T19282-2014 "Analysis Method for Lithium Hexafluorophosphate Products", pages 7-8 or the industry standard SJT 11723-2018 "Electrolyte for Lithium Ion Batteries", pages 3-5. The specific test steps are as follows:

[0240] 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 max<2cm) and 30mL ice water (temperature ≤4℃)], add 10 drops of bromothymol blue indicator solution, and quickly titrate with sodium hydroxide standard titration solution until the solution turns blue, which is the end point. At the end point, there should still be ice in the solution.

[0241] The analysis process should be completed within 20 seconds. At the same time, a blank test is carried out. Except for the absence of sample, the type and amount of other test solutions added to the blank test solution are the same as those of the test solution.

[0242] 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.

[0243] The content of hydrofluoric acid Y3 can be calculated by the following formula:

[0244] Y3=(V-V0)×c×M / (m×10 -3 ),

[0245] Wherein, V is the volume of sodium hydroxide standard titration solution consumed by titrating the test solution, in milliliters (mL); V0 is the volume of sodium hydroxide standard titration solution consumed by titrating the blank test solution, in milliliters (mL); c is the concentration of sodium hydroxide standard titration solution, in moles per liter (mol / L);

[0246] 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).

[0247] The arithmetic mean of the parallel measurement results is calculated according to the formula and taken as the measurement result. The ratio of the absolute difference between the two parallel measurement results to the arithmetic mean shall not exceed 20%.

[0248] (3) Preparation of negative electrode sheet

[0249] 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) are mixed in a mass ratio of 96:1:2:1, deionized water is added and stirred, and the negative electrode slurry is dispersed.

[0250] The negative electrode slurry is coated on the Cu foil. After both sides are completed, it is dried to form a negative electrode active layer, and then cold pressed, cut and sliced ​​to obtain a negative electrode sheet. The coating weight of the negative electrode active layer is 0.12g / 1540.25mm 2 The compacted density of the coating is 1.7g / cm 3 .

[0251] (4) Preparation of positive electrode

[0252] 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.

[0253] The positive electrode slurry is coated on the aluminum foil. After coating on both sides, it is dried to form a positive electrode active layer, and then cold pressed, cut and prepared to obtain a positive electrode sheet. The coating weight of the positive electrode active layer is 0.3g / 1540.25mm 2 , the compacted density of the coating is 4.2g / cm 3 .

[0254] (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.

[0255] The electrode assembly is placed in an outer package, and the above electrolyte is injected with an injection coefficient of 2.5 g / mAh, and packaging, injection, formation, exhaust and other processes are performed to obtain a lithium-ion secondary battery.

[0256] (6) Performance test of secondary batteries:

[0257] 1. Battery cycle test at 25℃

[0258] 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: at 25°C, the secondary batteries were allowed to stand for 30 minutes, then 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 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 with 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%.

[0259] Please see Table 1 for specific results.

[0260] 2. Battery 45℃ storage capacity retention test

[0261] At 25°C, the batteries of the above embodiments and comparative examples were charged at a constant current of 0.33C to a voltage of 4.45V, and 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 continuously 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 time the batteries were fully charged. The fully charged batteries were placed in a constant temperature box at 45°C for 180 days, and the batteries were taken out for capacity testing.

[0262] 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, see Table 1 for details.

[0263] 3. Transition metal Co deposition test

[0264] The batteries of the above-mentioned embodiments and comparative examples were discharged at a constant current of 0.33C to 2.5V, transferred to a glove box for disassembly, and the negative electrode sheet was retained. The negative electrode sheet was soaked in methyl formate at a mass ratio of 10:1, and the methyl formate was replaced every two hours, and replaced twice. After cleaning, the negative electrode sheet was transferred to a vacuum drying oven at 80°C for vacuum drying for 24 hours. About 2g of the negative electrode sheet was cut and digested into a solution with concentrated nitric acid, and the mass content of transition metal Co in the test solution was tested with an inductively coupled plasma emission spectrometer (icp-oes) (model iCAP 7400), and then the deposition amount of transition metal Co deposited on the entire negative electrode sheet was converted.

[0265] Embodiment 2-3

[0266] Examples 2 to 3 are basically the same as Example 1, except that: in step (1) of preparing the composite isolation, the type of functional polymer is different from that in Example 1, wherein Example 2 uses Li + Example 3 uses K + Type porous resin.

[0267] Among them, Example 2 uses Li + The porous resin is made by mixing the Na + The chelating resin (model CH-90) was immersed in a 10 wt% LiOH aqueous solution, wherein Na + The mass ratio of the type chelating resin to the LiOH aqueous solution is 1:10.

[0268] Example 2 Using K + The porous resin is made by mixing the Na +The chelating resin (model CH-90) was immersed in a 10 wt% KOH aqueous solution, wherein Na + The mass ratio of the type chelating resin to the KOH aqueous solution is 1:10.

[0269] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0270] Embodiments 4 to 7

[0271] Examples 4 to 7 are basically 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 in the example. Please see Table 1 for details.

[0272] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0273] Example 8

[0274] Example 8 is basically the same as Example 1, except that in step (1) of preparing 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.

[0275] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0276] Examples 9 to 13

[0277] Examples 9 to 13 are basically the same as Example 1, except that in step (1) of preparing the composite isolation, the particle size Dv50 of the functional polymer is different from that of Example 1. For details, please see Table 1.

[0278] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0279] Embodiments 14 to 19

[0280] Examples 14 to 19 are basically the same as Example 1, except that in the preparation of the composite insulation in step (1), the thickness H of the functional resin layer is different from that in Example 1. For details, please see Table 1.

[0281] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0282] Embodiment 20-21

[0283] 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.

[0284] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0285] Embodiments 22 to 25

[0286] 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.

[0287] 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%.

[0288] In Example 23, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC) and polyoxyethylene carbonate (PEC) 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%.

[0289] 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%.

[0290] In Example 25, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC) and polyvinyl chloride (PVC) 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%.

[0291] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0292] Embodiment 26

[0293] Example 26 is basically the same as Example 1, except that in the assembly step of the secondary battery, the functional resin layer on the composite isolation membrane is facing the negative electrode sheet.

[0294] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0295] Comparative Example 1

[0296] 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 the base film thickness of the composite isolation film in Example 1. Please see Table 1 for details.

[0297] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0298] Comparative Example 2

[0299] Comparative Example 2 is substantially the same as Example 1, except that: in the preparation of the electrolyte in step (2), the value of Y2 is different from that in Example 1. Specifically, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC) and ethylene carbonate (EC) are uniformly mixed in a mass ratio of 30:20:50 to obtain a mixed solvent, and the mass proportion of the solvent fluoroethylene carbonate (FEC) in the electrolyte is 8%. See Table 1 for details.

[0300] The other step conditions are the same as those in Example 1. The test results are shown in Table 1.

[0301] The relevant parameters and performance results of each embodiment and comparative example are shown in Table 1. Among them, the thickness of the functional resin layer is recorded as H; the mass of the cation contained in the functional resin layer per unit mass (1g) is recorded as Y1 (mg / g); in the electrolyte, based on the total mass of the solvent, the mass proportion of the cyclic carbonate is recorded as Y2; the content of hydrofluoric acid in the electrolyte is recorded as Y3.

[0302] Table 1

[0303]

[0304]

[0305] Note: In Table 1, “ / ” means that the substance or parameter does not exist.

[0306] 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 by adopting the technical solution of the present application, a good ion transfer rate is ensured while achieving directional capture of transition metal ions, thereby effectively improving the cycle performance and storage stability of the secondary battery.

[0307] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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.

[0308] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims, and the description and drawings can be used to interpret the content of the claims.

Claims

1. A secondary battery, characterized in that: 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 claim 1, wherein: The side chains of the functional polymer are grafted with the iminodiacetate groups.

4. The secondary battery according to claim 3, characterized in that: 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 claim 3, characterized in that: 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, characterized in that: 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 5, characterized in that: 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, characterized in that 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 claim 7, 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, characterized in that 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 claim 10, characterized in that: 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, characterized in that: 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, characterized in that: The electric device comprises the secondary battery according to any one of claims 1 to 12.

Images