Liquid polymer electrolyte, lithium ion battery and electric equipment

Abstract

The invention belongs to the technical field of secondary batteries, and particularly relates to a liquid polymer electrolyte, a lithium ion battery and electric equipment. According to the liquid polymer provided by the invention, the ionic conductivity and the lithium ion transference number of the liquid polymer can be improved by specifically limiting the composition of the main chain and the side chain, the liquid polymer is applied to a lithium ion battery, the normal charge and discharge requirements of the battery can be met, the internal concentration polarization of an electrolyte in the charge and discharge process of the battery is effectively avoided, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] The present application belongs to the technical field of secondary batteries, and specifically relates to a liquid polymer electrolyte, a lithium-ion battery, and an electrical device. Background Art

[0002] As the medium for ion transmission in lithium-ion batteries, the performance of electrolytes is directly related to the safety, energy density, and cycle stability of the battery. Traditional liquid small molecule electrolytes have low thermal stability, low boiling point, low decomposition temperature, and are highly flammable. They pose serious safety hazards under abnormal conditions such as overcharging and internal short circuits, limiting the application range and safety of the battery. Solid-state electrolytes (inorganic or organic) can effectively improve the safety performance of batteries due to their high thermal stability. However, inorganic solid-state electrolytes are sensitive to water and oxygen and have high costs; organic solid-state electrolytes have the defect of low room temperature conductivity; in addition, the solid-solid contact ability between solid-state electrolytes and electrode sheets is extremely poor, and the interface impedance at the interface is high. Therefore, solid-state electrolytes are still difficult to be applied in practice at this stage.

[0003] Liquid polymer electrolytes, as a transition state from liquid small molecules to solid electrolytes, can be customized according to specific application requirements. By adjusting the chemical structure and composition of the polymer to contain functional groups with specific functions, they can be used as lithium-ion battery electrolytes with the following advantages: 1. They can maintain their performance over a wider temperature range and are not easily decomposed at high temperatures; 2. Through functional group design, liquid polymer electrolytes can have a wider electrochemical window; 3. Liquid polymer electrolytes have a low glass transition temperature and appear as a fluid, viscous substance at room temperature, which can fully wet the interior and interface of the positive and negative electrodes, ensuring good contact at the interface. However, the research and development and application of this technology still face challenges.

[0004] Existing patents disclose a liquid polymer electrolyte. This liquid polymer is amorphous and contains ester and ether functional groups with ion-conducting properties. The fluorine groups in the polymer structure provide a certain degree of electrochemical stability, resulting in a high electrochemical window. However, this liquid polymer electrolyte has a long chain structure and no ion-conducting functional groups on the side chains. This limits its ion conductivity, resulting in low ionic conductivity and difficulty meeting the normal charge and discharge requirements of the battery. Furthermore, the low lithium ion transference number leads to concentration polarization within the electrolyte during the battery charge and discharge process, resulting in reduced battery cycle performance. Summary of the Invention

[0005] One of the purposes of the present invention is to provide a liquid polymer electrolyte to solve the problems of low ionic conductivity of liquid polymer electrolytes in the prior art, which makes it difficult to meet the normal charging and discharging requirements of the battery, low lithium ion migration number, and internal concentration polarization during the battery charging and discharging process, resulting in a decrease in the battery's cycle performance. The second purpose is to provide a lithium-ion battery; and the third purpose is to provide an electrical device.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The present application provides a liquid polymer electrolyte, comprising: a liquid polymer, a lithium salt, and a negative electrode film-forming additive, wherein the liquid polymer has a composition shown in the following general formula:

[0008]

[0009] Wherein, the value of q is an integer between 1 and 20, and the value of p is an integer between 1 and 20;

[0010] R1 is selected from at least one of H, C1-C11 alkyl, and C1-C11 alkoxy;

[0011] R2 is at least one selected from C1-C11 alkyl groups;

[0012] R3 is at least one selected from a C2-C23 nitrile group and a C2-C23 fluoroalkyl group.

[0013] According to the above technical means, this application can improve its ionic conductivity and lithium ion transference number by specifically limiting the composition of the main chain and side chain. When used in lithium-ion batteries, it can meet the normal charge and discharge requirements of the battery, effectively avoid the internal concentration polarization of the electrolyte during the battery charge and discharge process, and improve the battery cycle performance. Specifically, R1 in the liquid polymer is the alkyl side capping group of the polymer, and R2 is the ether side capping group. The alkyl and ether end capping ensures that it does not undergo electrochemical decomposition when used with a high-voltage positive electrode system. Among them, R3 is a substituent containing cyano or fluorine elements. By coordinating with the main chain structure, the presence of cyano and fluorine elements can further improve its electrochemical stability, making it suitable for high-voltage positive electrodes. The cyano-containing functional group can form a strong interaction with the surrounding anions due to its strong electron-withdrawing effect and polarity, thereby destroying the coordination structure of the lithium salt and promoting the dissociation of the lithium salt; and the fluorine group can also promote the dissociation of the lithium salt at the molecular level due to the high electronegativity and strong polarity of the fluorine atom. Through this dissociation ability, lithium ions can be more effectively released from the salt, thereby increasing the migration number of lithium ions, accelerating the transmission speed of lithium ions in the electrolyte, and ultimately improving the charge and discharge efficiency and cycle stability of the battery.

[0014] In some optional embodiments, R3 has any of the following structures:

[0015]

[0016] The value of n is an integer between 1 and 10; “*” represents the linking site.

[0017] According to the above technical means, the introduction of fluorine and nitrile functional groups into the side chains can effectively promote the dissociation of lithium salts through their strong electron-withdrawing effect and high polarity, thereby further increasing the number and concentration of lithium ion migration. In addition, these functional groups can enhance the ionic conductivity of the electrolyte, improve the interfacial compatibility between the electrolyte and the electrode, and further enhance the cycle stability of the battery.

[0018] In some optional embodiments, the molecular weight of the liquid polymer is 129-3200.

[0019] According to the above technical means, by controlling the molecular weight of the liquid polymer, not only the fluidity of the liquid polymer is effectively guaranteed, avoiding the poor fluidity of the liquid polymer, which leads to a decrease in ionic conductivity, but also the adhesion of the polymer is effectively guaranteed, which is beneficial to improving the electrode interface contact effect.

[0020] In some optional embodiments, based on the total mass of the liquid polymer electrolyte, the mass percentage of the liquid polymer is 65%-84%.

[0021] In some optional embodiments, based on the total mass of the liquid polymer electrolyte, the mass percentage of the lithium salt is 15%-30%.

[0022] In some optional embodiments, the lithium salt includes but is not limited to at least one of lithium perchlorate, lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate and lithium bis(fluoromethanesulfonyl)imide.

[0023] In some optional embodiments, the mass percentage of the negative electrode film-forming additive is 1%-5% based on the total mass of the liquid polymer electrolyte.

[0024] In some optional embodiments, the negative electrode film-forming additive is preferably an organic small molecule additive, including at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, propylene sulfate, 4-methylethylene sulfate, vinyl carbonate, 4-ethylethylene sulfate, 1,3-propane sultone, vinyl vinyl sulfite, tris(trimethylsilyl)borate and.

[0025] According to the above technical means, the use of negative electrode film-forming additives can form a solid electrolyte interface film (SEI film) at the negative electrode, reducing Li+ The energy barrier for transport inhibits the growth of Li dendrites and can also prevent some functional groups in the liquid polymer from reacting with the negative electrode, thereby improving the cycle performance of the battery.

[0026] According to another aspect of the present application, a lithium-ion battery is provided, comprising: a positive electrode sheet, a negative electrode sheet, a separator and the above-mentioned liquid polymer electrolyte.

[0027] According to the above technical means, the lithium-ion battery provided in the present application adopts the liquid polymer electrolyte provided above in the present application. Since the liquid polymer has a high ionic conductivity and a high lithium ion transfer number, it can avoid the concentration polarization inside the lithium-ion battery during the charge and discharge process, thereby improving the battery cycle performance.

[0028] In some optional embodiments, the liquid polymer electrolyte is filled in the separator.

[0029] The liquid polymer electrolyte provided in this application is in liquid state at room temperature and cannot form a film independently. There are a large number of gaps inside the diaphragm, which has the ability to absorb liquid. After filling with the liquid polymer electrolyte, the pores of the diaphragm can be ensured to be fully infiltrated to form a continuous ion channel, reducing the resistance to ion migration. After filling, the liquid polymer electrolyte is evenly distributed between the positive and negative electrodes, avoiding polarization caused by local uneven ion concentration.

[0030] In some optional embodiments, the separator includes one of a polyethylene separator, a polypropylene separator, a polyethylene-polypropylene composite separator, a glass fiber cloth, a non-woven fabric, a silica aerogel and a cellulose membrane.

[0031] According to another aspect of the present application, there is also provided an electrical device comprising the above-mentioned lithium-ion battery.

[0032] Beneficial effects of the present invention:

[0033] (1) The liquid polymer electrolyte provided in the present application comprises: a liquid polymer, a lithium salt and a negative electrode film-forming additive. A liquid polymer with a specific composition is selected. By specifically limiting the composition of the main chain and the side chain, especially by introducing a nitrile group with a strong electron-withdrawing effect or a highly electronegative fluorine element functional group, its ionic conductivity and lithium ion migration number can be improved. Alkyl or alkoxy groups are used as end-capping groups to ensure good compatibility of the electrolyte with high-voltage positive electrode materials, reduce the occurrence of side reactions, and enable it to meet the normal charging and discharging requirements of the battery.

[0034] (2) The liquid polymer electrolyte provided herein, through the specific definition of side chain functional groups, can effectively promote the dissociation of lithium salts through their strong electron-withdrawing effect and high polarity, thereby further increasing the number and concentration of lithium ion transfer. In addition, these functional groups can also enhance the ionic conductivity of the electrolyte and improve the interfacial compatibility between the electrolyte and the electrode.

[0035] (3) The liquid polymer electrolyte provided in this application not only effectively ensures the fluidity of the liquid polymer by controlling the molecular weight of the liquid polymer, thereby avoiding the poor fluidity of the liquid polymer, which leads to a decrease in ionic conductivity, but also effectively ensures the adhesion of the polymer, which is beneficial to improving the electrode interface contact effect.

[0036] (4) The liquid polymer electrolyte provided by this application and the negative electrode film-forming additive can form a solid electrolyte interface film (SEI film) at the negative electrode, reducing Li + The energy barrier for transport inhibits the growth of Li dendrites and can also prevent some functional groups in the liquid polymer from reacting with the negative electrode, thereby improving the cycle performance of the battery.

[0037] (5) The lithium-ion battery provided in the present application adopts the liquid polymer electrolyte provided above in the present application. Since the liquid polymer has high ionic conductivity and lithium ion migration number, it can meet the normal charging and discharging requirements of the battery, making it adaptable to high-voltage positive electrodes, broadening the electrochemical window, avoiding the internal concentration polarization of the electrolyte during the battery charging and discharging process, and improving the battery cycle performance.

[0038] (6) In the lithium-ion battery provided in the present application, the liquid polymer electrolyte is filled in the diaphragm, which can ensure that it fully infiltrates the pores of the diaphragm, forms a continuous ion channel, and reduces the resistance to ion migration. After filling, the liquid polymer electrolyte is evenly distributed between the positive and negative electrodes, avoiding polarization caused by local uneven ion concentration.

[0039] (7) The electrical equipment provided in this application has the same advantages as the above-mentioned lithium-ion batteries due to the use of the lithium-ion batteries provided in this application, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a cyclic charge and discharge data diagram of Example 1 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0041] The following describes the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art will readily appreciate the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the various details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are intended only to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0042] It should be noted that the illustrations provided in the following embodiments are merely schematic illustrations of the basic concept of the present invention. Therefore, the illustrations only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed arbitrarily, and the component layout may also be more complex.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are for the purpose of describing specific embodiments only and are not intended to limit this application; the terms "including" and "having" and any variations thereof in this application text are intended to cover non-exclusive inclusions.

[0044] 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.

[0045] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of the end values ​​and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. In this application, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein, and "0-5" is just an abbreviation of these numerical combinations. In addition, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter can be, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0046] In the description of the embodiments of the present application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent three situations: A exists alone, A and B exist at the same time, and B exists alone.

[0047] In the description of the embodiments of the present application, the term "at least one" refers to one or more than two (including two).

[0048] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0049] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0050] As described in the background technology, the ionic conductivity and ion transference number of the liquid polymer electrolyte in the prior art are low, which affects the electrochemical window and cycle performance of the battery. To this end, the following technical solutions are provided:

[0051] The present application provides a liquid polymer electrolyte, comprising: a liquid polymer, a lithium salt, and a negative electrode film-forming additive, wherein the liquid polymer has a composition shown in the following general formula:

[0052]

[0053] Wherein, the value of q is an integer between 1 and 20, and the value of p is an integer between 1 and 20;

[0054] R1 is selected from at least one of H, C1-C11 alkyl, and C1-C11 alkoxy;

[0055] R2 is at least one selected from C1-C11 alkyl groups;

[0056] R3 is at least one selected from a C2-C23 nitrile group and a C2-C23 fluoroalkyl group.

[0057] As an example, the value of q can be 1, 3, 5, 7, 9, 10, 12, 14, 15, 16, 18, 20, or a range thereof; the value of p can be 1, 3, 5, 7, 9, 10, 12, 14, 15, 16, 18, 20, or a range thereof. R1 can be selected from H, methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, heptyl, octyl, decyl, undecyl, methoxy, ethoxy, propoxy, C4 alkoxy, C5 alkoxy, C6 alkoxy, C7 alkoxy, C8 alkoxy, C9 alkoxy, C10 alkoxy, C11 alkoxy, etc., R2 can be selected from methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, heptyl, octyl, decyl, undecyl, etc.; the C2-C23 nitrile group can contain 1, 2 or 3 nitrile groups, and the C2-C23 fluoroalkyl group can contain 1, 2 or 3 trifluoromethyl groups, etc.

[0058] According to the above technical means, by specifically limiting the composition of the main chain and side chain, its ionic conductivity and lithium ion migration number can be improved, and it can be used in lithium-ion batteries to meet the normal charge and discharge requirements of the battery, effectively avoid the internal concentration polarization of the electrolyte during the charge and discharge process of the battery, and improve the battery cycle performance. Specifically, R1 in the liquid polymer is the alkyl side capping group of the polymer, and R2 is the ether side capping group. Capping with an alkyl or ether group can ensure that it does not undergo electrochemical decomposition when used in conjunction with a high-voltage positive electrode system. Among them, R3 is a substituent containing a cyano group or a fluorine element. By coordinating with the main chain structure, the presence of cyano and fluorine elements can further improve its electrochemical stability, making it suitable for high-voltage positive electrodes. The cyano-containing functional group, due to its strong electron-withdrawing effect and polarity, can form a strong interaction with the surrounding anions, thereby destroying the coordination structure of the lithium salt and promoting the dissociation of the lithium salt; and the fluorine group, due to the high electronegativity and strong polarity of the fluorine atom, can also promote the dissociation of the lithium salt at the molecular level. Through this dissociation ability, lithium ions can be released from the salt more efficiently, thereby increasing the migration number of lithium ions, accelerating the transmission speed of lithium ions in the electrolyte, and ultimately improving the battery's charge and discharge efficiency and cycle stability.

[0059] It should be noted that the liquid polymer used in this application can be obtained through commercial channels, can be customized from reagent manufacturers according to needs, and can also be prepared using methods known in the art.

[0060] In some optional embodiments, R3 has any of the following structures:

[0061]

[0062]

[0063] Wherein, the value of n is an integer between 1 and 10; "*" represents a linking site. As an example, the value of n can be 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0064] According to the above technical means, the introduction of fluorine and nitrile functional groups into the side chains can effectively promote the dissociation of lithium salts through their strong electron-withdrawing effect and high polarity, thereby further increasing the number and concentration of lithium ion migration. In addition, these functional groups can enhance the ionic conductivity of the electrolyte, improve the interfacial compatibility between the electrolyte and the electrode, and further enhance the cycle stability of the battery.

[0065] In some optional embodiments, the molecular weight of the liquid polymer is 129-3200. As an example, the molecular weight of the liquid polymer can be 129, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, 1500, 1800, 2000, 2300, 2500, 2700, 3000, 3200, or any range thereof.

[0066] According to the above technical means, by controlling the molecular weight of the liquid polymer, not only the fluidity of the liquid polymer is effectively guaranteed, avoiding the poor fluidity of the liquid polymer, which leads to a decrease in ionic conductivity, but also the adhesion of the polymer is effectively guaranteed, which is beneficial to improving the electrode interface contact effect.

[0067] In some optional embodiments, the mass percentage of the liquid polymer in the liquid polymer electrolyte is 65%-84%, based on the total mass of the liquid polymer electrolyte. As an example, the mass percentage of the liquid polymer in the liquid polymer electrolyte can be 65%, 68%, 70%, 72%, 75%, 77%, 80%, 82%, 84%, or any range thereof.

[0068] In some optional embodiments, the mass percentage of the lithium salt is 15%-30% based on the total mass of the liquid polymer electrolyte; as an example, the mass percentage of the lithium salt in the liquid polymer electrolyte can be 15%, 17%, 19%, 20%, 22%, 24%, 25%, 26%, 28%, 30%, or within the range of any of the above values.

[0069] In some optional embodiments, the lithium salt includes but is not limited to at least one of lithium perchlorate, lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate and lithium bis(fluoromethanesulfonyl)imide.

[0070] In some optional embodiments, the mass percentage of the negative electrode film-forming additive is 1%-5% based on the total mass of the liquid polymer electrolyte; as an example, the mass percentage of the film-forming additive in the liquid polymer electrolyte can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or within the range of any of the above values.

[0071] In some optional embodiments, the negative electrode film-forming additive is preferably an organic small molecule additive, including at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, propylene sulfate, 4-methylethylene sulfate, vinyl carbonate, 4-ethylethylene sulfate, 1,3-propane sultone, vinyl vinyl sulfite, tris(trimethylsilyl)borate and.

[0072] According to the above technical means, the use of negative electrode film-forming additives can form a solid electrolyte interface film (SEI film) at the negative electrode, reducing Li + The energy barrier for transport inhibits the growth of Li dendrites and can also prevent some functional groups in the liquid polymer from reacting with the negative electrode, thereby improving the cycle performance of the battery.

[0073] In the present application, the preparation method of the liquid polymer electrolyte is not specifically limited. For example, the liquid polymer electrolyte can be obtained by dissolving lithium salt and negative electrode film-forming additives in a liquid polymer.

[0074] According to another aspect of the present application, a lithium-ion battery is provided, comprising: a positive electrode sheet, a negative electrode sheet, a separator and the above-mentioned liquid polymer electrolyte.

[0075] The lithium-ion battery provided in the present application adopts the liquid polymer electrolyte provided above in the present application. Since the liquid polymer has high ionic conductivity and lithium ion transference number, it can meet the normal charging and discharging requirements of the battery, making it adaptable to high-voltage positive electrodes, widening the electrochemical window, avoiding concentration polarization inside the electrolyte during the battery charging and discharging process, and improving the battery cycle performance.

[0076] In some optional embodiments, the liquid polymer electrolyte is filled in the separator.

[0077] The liquid polymer electrolyte provided in this application is in liquid state at room temperature and cannot form a film independently. There are a large number of gaps inside the diaphragm, which has the ability to absorb liquid. The liquid polymer electrolyte is filled in the diaphragm to ensure that it fully infiltrates the pores of the diaphragm, forming a continuous ion channel and reducing the resistance to ion migration. After filling, the liquid polymer electrolyte is evenly distributed between the positive and negative electrodes, avoiding polarization caused by local uneven ion concentration.

[0078] In some optional embodiments, the separator is conventional in the art, including but not limited to one of polyethylene separator, polypropylene separator, polyethylene-polypropylene composite separator, glass fiber cloth, non-woven fabric, silica aerogel and cellulose membrane.

[0079] According to another aspect of the present application, there is also provided an electrical device comprising the above-mentioned lithium-ion battery.

[0080] The electrical equipment provided in this application has the same advantages as the above-mentioned lithium-ion batteries due to the use of the lithium-ion batteries provided in this application, which will not be described in detail here.

[0081] It is understood by those skilled in the art that during the charge and discharge process of the battery, lithium ions are embedded and extracted back and forth between the positive electrode and the negative electrode. The diaphragm filled with liquid polymer electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The diaphragm is arranged between the positive electrode and the negative electrode, and mainly plays the role of preventing the positive and negative electrodes from short-circuiting, while allowing lithium ions to pass through.

[0082] As an example, the positive electrode sheet includes a positive electrode collector and a positive electrode active material layer, the positive electrode collector has two surfaces opposite to each other in its own thickness direction, the positive electrode active material layer is arranged on any one or both of the two opposite surfaces of the positive electrode collector, and the positive electrode active material layer is composed of a positive electrode active material, a binder, and a conductive agent in a certain mass ratio. The materials, composition and manufacturing method of the positive electrode sheet used in the lithium-ion battery of the present application may include any technology disclosed in the prior art. For example, the positive electrode active material is selected from one or more of lithium cobalt oxide materials, lithium iron phosphate materials, nickel cobalt manganese ternary materials, nickel cobalt aluminum ternary materials, spinel nickel manganese oxide materials and lithium-rich manganese materials; the binder is selected from at least one of polyvinylidene fluoride, polyacrylic acid, sodium carboxymethyl cellulose and styrene-butadiene rubber; the conductive agent is selected from at least one of conductive graphite, conductive carbon black (Super P), carbon nanotubes and graphene.

[0083] As an example, a negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector has two surfaces facing each other in the thickness direction of the negative electrode current collector, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector. The materials, composition, and manufacturing methods of the negative electrode sheet used in the lithium-ion battery of the present application may include any technology disclosed in the prior art. For example, the negative electrode active material includes at least one of a carbon material, metallic lithium, a metal alloy, a lithium-containing oxide, and a silicon-containing material.

[0084] The material and shape of the separator used in the lithium-ion battery of the present application are not particularly limited and may include any technology disclosed in the prior art. As an example, the separator is selected from one or more of a polyethylene separator, a polypropylene separator, a polyethylene-polypropylene composite separator, a glass fiber cloth, a non-woven fabric, a silica aerogel, and a cellulose membrane.

[0085] The present application does not specifically limit the preparation method of the lithium-ion battery; conventional preparation methods in the art may be used to prepare the lithium-ion secondary battery. For example, the positive electrode sheet, the separator, and the negative electrode sheet are sequentially stacked, with the separator positioned between the positive and negative electrode sheets, and a cell is obtained by stacking or winding the sheets. The cell is then baked, injected with the aforementioned liquid polymer electrolyte, and then subjected to steps such as formation and packaging to obtain the lithium-ion secondary battery of the present application.

[0086] It is understood that in the electrical equipment provided herein, the lithium-ion battery can be used as a power source for the electrical equipment or as an energy storage unit for the electrical equipment. The electrical equipment may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0087] The present application is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present application in any way.

[0088] Example 1

[0089] The present application provides a liquid polymer electrolyte, the composition and specific preparation method of which are as follows:

[0090] The liquid polymer, lithium bis(fluoromethanesulfonyl)imide, and fluoroethylene carbonate were mixed in a mass ratio of 77:20:3 to obtain a liquid polymer electrolyte, wherein the liquid polymer has the following structural formula:

[0091]

[0092] Among them, R1 is H, R2 is -CH3; the structural formula of R3 is The value of q is 5, and the value of p is 10.

[0093] Example 2

[0094] The present application provides a liquid polymer electrolyte, the composition and specific preparation method of which are as follows:

[0095] The liquid polymer, lithium bis(fluoromethanesulfonyl)imide, and fluoroethylene carbonate were mixed in a mass ratio of 80:17:3 to obtain a liquid polymer electrolyte, wherein the liquid polymer has the following structural formula:

[0096]

[0097] Among them, R1 is -CH3, R2 is -CH3; the structural formula of R3 is The value of q is 5, and the value of p is 10.

[0098] Example 3

[0099] The present application provides a liquid polymer electrolyte, the composition and specific preparation method of which are as follows:

[0100] The liquid polymer, lithium bis(fluoromethanesulfonyl)imide, and fluoroethylene carbonate were mixed in a mass ratio of 80:18:2 to obtain a liquid polymer electrolyte, wherein the liquid polymer has the following structural formula:

[0101]

[0102] Among them, R1 is -OCH3, R2 is -OCH3; the structural formula of R3 is The value of q is 5, and the value of p is 10.

[0103] Example 4

[0104] The present application provides a liquid polymer electrolyte, the composition and specific preparation method of which are as follows:

[0105] The liquid polymer, lithium bis(fluoromethanesulfonyl)imide, and fluoroethylene carbonate were mixed in a mass ratio of 77:20:3 to obtain a liquid polymer electrolyte, wherein the liquid polymer has the following structural formula:

[0106]

[0107] Among them, R1 is H, R2 is -CH3; the structural formula of R3 is -CH2-CN, q is 5, and p is 10.

[0108] Example 5

[0109] The present application provides a liquid polymer electrolyte, the composition and specific preparation method of which are as follows:

[0110] The liquid polymer, lithium bis(fluoromethanesulfonyl)imide, and fluoroethylene carbonate were mixed in a mass ratio of 80:17:3 to obtain a liquid polymer electrolyte, wherein the liquid polymer has the following structural formula:

[0111]

[0112] Among them, R1 is -CH3, R2 is -CH3; the structural formula of R3 is -CH2-CF3, q is 5, and p is 10.

[0113] Example 6

[0114] The present application provides a liquid polymer electrolyte. Compared with Example 1, the difference is that the value of q in the liquid polymer is 2, and the value of p is 4.

[0115] Example 7

[0116] The present application provides a liquid polymer electrolyte, which is different from Example 1 in that: R3 in the liquid polymer is n=8.

[0117] Example 8

[0118] The present application provides a liquid polymer electrolyte. Compared with Example 1, the difference is that R1 in the liquid polymer is OCH2CH3 and R2 is -(CH2)7CH3.

[0119] Example 9

[0120] The present application provides a liquid polymer electrolyte. Compared with Example 1, the difference is that the liquid polymer, lithium bis(fluoromethanesulfonyl)imide and fluoroethylene carbonate are mixed in a mass ratio of 65:15:5.

[0121] Example 10

[0122] The present application provides a liquid polymer electrolyte, which is different from Example 1 in that the lithium salt is lithium hexafluorophosphate and the negative electrode film-forming additive is 1,3-propane sultone.

[0123] Example 11

[0124] This embodiment provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and the liquid polymer electrolyte provided in Example 1. The positive electrode active material is lithium iron phosphate, the negative electrode active material is metallic lithium, and the separator is a polyethylene separator. A bare cell is assembled in a positive electrode-separator-negative electrode structure. The lithium-ion secondary battery is obtained through baking, injection of the liquid polymer electrolyte, formation, and packaging. Specifically:

[0125] Preparation of the positive electrode sheet: A 13μm-thick aluminum foil was used as the positive electrode current collector. Lithium iron phosphate, carbon black as a conductive agent, and polyvinylidene fluoride as a binder were thoroughly mixed in a suitable amount of NMP solvent at a weight ratio of 94:3:3 to form a uniform positive electrode slurry. The positive electrode slurry was evenly coated on the surface of the positive electrode current collector aluminum foil. After drying and cold pressing, the positive electrode sheet was obtained.

[0126] Preparation of the negative electrode sheet: 8μm-thick copper foil was used as the negative electrode current collector. The negative electrode active material, graphite, the binder, styrene-butadiene rubber, the thickener, sodium carboxymethyl cellulose, and the conductive agent, carbon black, were thoroughly mixed in a weight ratio of 95:2:2:1 in an appropriate amount of deionized water to form a uniform negative electrode slurry. This slurry was evenly coated on the surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet was obtained.

[0127] Example 12-Example 20

[0128] This embodiment provides a lithium ion battery. Compared with embodiment 11, the difference lies in that the liquid polymer electrolytes in embodiments 2-10 are selected in sequence.

[0129] Comparative Example 1

[0130] This comparative example provides a liquid polymer electrolyte, which differs from Example 1 in that conventional polyethylene glycol dimethyl ether (Mn is about 500) is used instead of the liquid polymer in Example 1;

[0131] This comparative example also provides a lithium-ion battery, which differs from Example 11 in that the liquid polymer electrolyte provided in this comparative example is used.

[0132] Comparative Example 2

[0133] This comparative example provides a liquid polymer electrolyte and a lithium ion battery. The difference from comparative example 1 is that the molecular weight Mn of polyethylene glycol dimethyl ether is about 1000.

[0134] Comparative Example 3

[0135] This comparative example provides a liquid polymer electrolyte and a lithium ion battery. The difference compared with comparative example 1 is that the liquid polymer DEG-EDT obtained in Example 1 of CN111326797A is used instead of conventional polyethylene glycol dimethyl ether (Mn-500).

[0136] Comparative Example 4

[0137] This comparative example provides a liquid polymer electrolyte and a lithium ion battery. The difference compared with comparative example 1 is that polyacrylonitrile (Mn is about 100,000) is used instead of the liquid polymer.

[0138] Comparative Example 5

[0139] This comparative example provides a liquid polymer electrolyte and a lithium ion battery. The difference from comparative example 1 is that polyvinylidene fluoride (Mn is about 100,000) is used instead of the liquid polymer.

[0140] Test Case

[0141] 1) Lithium ion conductivity test

[0142] The liquid polymer electrolytes provided in Examples 1 to 10 and Comparative Examples 1 to 5 were subjected to lithium ion conductivity tests. The specific operating steps were as follows: a sandwich-structured button cell with a diameter of 16 mm was assembled using stainless steel sheets to test the AC impedance spectrum of the ion conduction layer, with a bias voltage of 10 mV, a test frequency of 1 MHz to 1 Hz, and a test temperature of 25°C.

[0143] 2) Lithium ion migration number test

[0144] The liquid polymer electrolyte is adsorbed in the polyethylene separator, and then the button cell is assembled in the "lithium sheet / separator / lithium sheet" manner. The assembled battery is tested on an electrochemical workstation with a polarization potential of 10mV. The impedance of the battery before and after polarization is measured by electrochemical impedance spectroscopy. The initial current and steady-state current are obtained by the steady-state current method, and the data are brought into tLi + =Is(△V-Ro·Io) / Io(△V-Rs·Is), calculate the lithium ion migration number tLi + , where Io is the initial current, Is is the steady-state current, Ro is the initial resistance, Rs is the steady-state resistance, and △V is the polarization voltage.

[0145] 3) Electrochemical window test

[0146] The electrochemical workstation conducted a linear sweep voltammetry test. The liquid polymer electrolyte was adsorbed into a polyethylene diaphragm, and then a button cell was assembled in the "lithium sheet / diaphragm / stainless steel sheet" manner. The test voltage range was 2.5V-5.5V, and the scan rate was 0.01mV / s. When the test current deviated significantly from the baseline, an extension line was drawn from the baseline to intersect with the X-axis. The intersection value was the electrochemical window value.

[0147] 4) Cyclic charge and discharge test

[0148] A battery testing system was used to conduct cyclic charge-discharge tests on the lithium-ion batteries provided in Examples 11-20 and Comparative Examples 1-5. The specific procedures were as follows: The battery cycling performance was tested at a voltage of 2.5V-4.4V. At a constant temperature of 25°C, the battery was charged at 0.2C to 4.4V, then charged at 4.4V with a constant voltage until the current was less than 0.05mA. After standing for 5 minutes, the battery was discharged at 0.2C to 2.5V, and the discharge capacity (E0) at this point was recorded. The charge and discharge cycle was repeated 100 times, and the discharge capacity (E1) after 100 cycles was recorded. The cycle capacity retention rate was calculated as E0 / E1 × 100%.

[0149] See the table below for specific test results.

[0150] Table 1

[0151]

[0152] Note: The cycle capacity retention rate is the test results of lithium-ion battery Examples 11 to 20 corresponding to Examples 1 to 10.

[0153] From Table 1 and Figure 1 The test results can be analyzed to conclude that the liquid polymer electrolyte described in the present application performs well in terms of ionic conductivity, lithium ion migration number and electrochemical window. Compared with the unmodified comparative examples 1 and 2, the various properties of the electrolyte of the present application are significantly improved. It can be seen from the test results of the embodiments and comparative examples that if the main chain is different, even if the side chain contains a nitrile group or a fluorine group, the improvement in ionic conductivity and lithium ion migration number is not obvious, indicating that the improvement in the performance of the present application is mainly attributed to the synergistic effect between the polymer main chain structure and the nitrile group and fluorine group introduced in the side chain. The main chain provides good physical support and structural stability, while the nitrile group and fluorine group in the side chain effectively promote the dissociation of lithium salts and increase the transfer sites of lithium ions through their high polarity and electron-withdrawing effect. At the same time, the high oxidation resistance of the nitrile group and fluorine group themselves broadens the electrochemical window of the electrolyte. In summary, the liquid polymer electrolyte has high ionic conductivity and a wide electrochemical window, can be used as a high-performance lithium-ion battery electrolyte, and successfully solves the problems of low ionic conductivity and lithium ion migration number in traditional liquid polymer electrolytes.

[0154] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A liquid polymer electrolyte, characterized in that include: Liquid polymer, lithium salt and negative electrode film-forming additive, wherein the liquid polymer has a composition shown in the following general formula: Wherein, the value of q is an integer between 1 and 20, and the value of p is an integer between 1 and 20; R1 is selected from at least one of H, C1-C11 alkyl, and C1-C11 alkoxy; R2 is at least one selected from C1-C11 alkyl groups; R3 is at least one selected from a C2-C23 nitrile group and a C2-C23 fluoroalkyl group.

2. The liquid polymer electrolyte according to claim 1, characterized in that R3 has any of the following structures: The value of n is an integer between 1 and 10; "*" represents the linking site.

3. The liquid polymer electrolyte according to claim 1, characterized in that The molecular weight of the liquid polymer is 129-3200.

4. The liquid polymer electrolyte according to any one of claims 1 to 3, characterized in that Based on the total mass of the liquid polymer electrolyte, the mass percentage of the liquid polymer is 65%-84%.

5. The liquid polymer electrolyte according to any one of claims 1 to 3, characterized in that The mass percentage of the lithium salt is 15%-30% based on the total mass of the liquid polymer electrolyte; And / or, the lithium salt includes at least one of lithium perchlorate, lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate and lithium bis(fluoromethanesulfonyl)imide.

6. The liquid polymer electrolyte according to any one of claims 1 to 3, characterized in that The mass percentage of the negative electrode film-forming additive is 1%-5% based on the total mass of the liquid polymer electrolyte; And / or, the negative electrode film-forming additive includes at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, propylene sulfate, 4-methylethylene sulfate, vinylethylene carbonate, 4-ethylethylene sulfate, 1,3-propane sultone, vinylethylene sulfite, and tris(trimethylsilyl)borate.

7. A lithium-ion battery, characterized in that: include: A positive electrode sheet, a negative electrode sheet, a separator and a liquid polymer electrolyte according to any one of claims 1 to 6.

8. The lithium-ion battery according to claim 7, characterized in that The liquid polymer electrolyte is filled in the separator.

9. The lithium-ion battery according to claim 8, characterized in that The separator includes one of a polyethylene separator, a polypropylene separator, a polyethylene-polypropylene composite separator, a glass fiber cloth, a non-woven fabric, a silica aerogel and a cellulose membrane.

10. An electrical device, characterized in that: A lithium-ion battery comprising the lithium-ion battery according to any one of claims 7 to 9.

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