Electrolyte additive, battery, battery pack and energy storage system

Abstract

The invention provides an electrolyte additive, a battery, a battery pack and an energy storage system. The molecular structure of the electrolyte additive comprises at least one of oxygen atoms and sulfur atoms and a nitrogen-containing heterocyclic ring, and the nitrogen-containing heterocyclic ring comprises at least one of carbon-nitrogen double bonds and nitrogen-nitrogen double bonds. The oxygen atoms are used for forming carbon-oxygen double bonds with carbon atoms on the nitrogen-containing heterocyclic ring, and the sulfur atoms are used for forming carbon-sulfur double bonds with the carbon atoms on the nitrogen-containing heterocyclic ring. The structure of the additive enables the additive to have a film-forming property, and the additive reacts with the positive electrode and the negative electrode on a solid-liquid phase interface, so that passive films are formed on the surfaces of the positive electrode and the negative electrode. And the stability of the battery and the high-temperature cycle performance and low-temperature performance of the battery are improved through the formation of the passive film, so that the battery can be used in a wide temperature range.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an electrolyte additive, a battery, a battery pack and an energy storage system. Background Art

[0002] Secondary batteries and energy storage system devices that integrate secondary batteries inevitably need to be used under high temperature conditions. When secondary batteries are used at high temperatures, they are prone to bloating and capacity decay too quickly, resulting in poor user experience and safety risks. High-temperature bloating and capacity decay of secondary batteries are essentially side reactions at the battery interface, especially electrolyte oxidation and the reaction between the battery's positive electrode and the electrolyte. To address this problem, additives are added to the electrolyte to participate in film formation to improve the performance of the electrolyte or electrode interface, but existing additives cannot bring ideal results, and it is difficult to solve the problems of poor high-temperature performance and high low-temperature impedance of secondary batteries. Summary of the invention

[0003] The present application provides an electrolyte additive, a battery, a battery pack and an energy storage system.

[0004] In a first aspect, the present application provides an electrolyte additive, wherein the molecular structure of the additive includes at least one of an oxygen atom and a sulfur atom, and a nitrogen-containing heterocyclic ring, wherein the nitrogen-containing heterocyclic ring includes at least one of a carbon-nitrogen double bond and a nitrogen-nitrogen double bond. The oxygen atom forms a carbon-oxygen double bond with a carbon atom on the nitrogen-containing heterocyclic ring, and the sulfur atom forms a carbon-sulfur double bond with a carbon atom on the nitrogen-containing heterocyclic ring.

[0005] In the embodiments of the present application, the structural structure of the additive enables it to have film-forming properties. During the first charging process of the battery, the additive reacts with the positive electrode and the negative electrode at the solid-liquid interface to form a passivation film on the surface of the positive electrode and the negative electrode. The formation of the passivation film can reduce the side reactions of the electrolyte with the positive electrode or the negative electrode, and can inhibit the decomposition of the electrolyte, thereby improving the stability of the battery and the high-temperature cycle performance and low-temperature performance of the battery, so that the battery can be used in a wide temperature range. The structural characteristics of the additive make the passivation film formed by the additive have more excellent performance, which is beneficial to improving the overall performance of the battery.

[0006] On the one hand, the nitrogen-containing heterocycle in the molecular structure of the additive can improve the stability of the passivation film. The connected nitrogen atoms increase the nitrogen density of the local structure of the additive, and the nitrogen atoms can provide more lone pairs of electrons to make it easier for the additive to form a film on the positive electrode. For the passivation film formed on the surface of the negative electrode, since the additive is rich in nitrogen, the passivation film formed by the additive is rich in nitrogen. For example, the passivation film includes nitrides, which improves the ion conductivity of the passivation film and reduces the impedance of the passivation film.

[0007] On the other hand, the unsaturated bonds in the molecular structure of the additive help to form a passivation film containing the polymer, thereby improving the mechanical properties of the entire passivation film. The battery is not easily broken due to gas production during the charge and discharge process, which makes the battery have good cycle performance.

[0008] On the other hand, the oxygen atom or sulfur atom has a lone pair of electrons, which can coordinate with the metal element in the positive electrode to cover the positive electrode active site, so that the passivation film formed by the additive can effectively inhibit the side reactions on the positive electrode surface. And the nitrogen atom in the nitrogen-containing heterocycle and the sulfur atom in the oxygen-containing sulfur substituent group can increase the reduction potential of the entire additive molecule, making it easier for the additive to participate in film formation. In addition, a double bond is formed between the oxygen atom or sulfur atom and the nitrogen-containing heterocycle, and the electron-deficient divalent sulfur atom has two positive potential regions. The introduction of divalent sulfur atoms will bring about changes in the molecular electron cloud, which can greatly improve the affinity of the compound, so that the additive can be directed to poison the active sites on the surface of the positive electrode of the battery, greatly inhibiting the side reactions on the positive electrode surface. The divalent oxygen atom will affect the electron cloud of the nitrogen-containing heterocycle, which can increase the reduction potential of the entire additive molecule, making it easy for the additive to participate in film formation.

[0009] In one embodiment, the nitrogen-containing heterocycle also includes at least one of a carbon-carbon double bond, a nitrogen-nitrogen single bond, and a carbon-nitrogen single bond. In the embodiment of the present application, the double bond in the nitrogen-containing heterocycle can increase the electron cloud distribution. When the unsaturated bond includes a carbon-nitrogen double bond, the carbon-nitrogen electron cloud is unevenly distributed, biased toward the nitrogen atom, which can reduce the LUMO orbital energy of the additive molecule, making the additive more likely to undergo reduction polymerization to form a passivation film on the positive and negative electrode surfaces. At the same time, double bonds such as carbon-nitrogen double bonds, nitrogen-nitrogen double bonds, and carbon-carbon double bonds can form a passivation film of the polymer component, improve the mechanical properties of the passivation film, and when the passivation film is formed on the negative electrode surface, the negative electrode can be made not easily broken when the volume shrinks during overcharge during charge and discharge. In addition, the formation of nitrogen-nitrogen single bonds and carbon-nitrogen single bonds increases the nitrogen density of the local structure of the additive, and nitrogen atoms can provide more lone pairs of electrons to make the additive easier to form a film on the positive electrode. For the passivation film formed on the surface of the negative electrode, since the additive is rich in nitrogen, the passivation film formed by the additive is rich in nitrogen. Exemplarily, the passivation film includes nitride, which improves the ion conductivity of the passivation film and reduces the impedance of the passivation film.

[0010] In one embodiment, the nitrogen-containing heterocycle includes three nitrogen atoms, two of the three nitrogen atoms are connected to form a nitrogen-nitrogen single bond, and another nitrogen atom of the three nitrogen atoms is connected to two carbon atoms. In the embodiment of the present application, the nitrogen atom has a higher electronegativity. When the additive forms a passivation film, the nitrogen atom can form a nitride with a metal such as Li, Na, etc. with a lower electronegativity. The nitride has an excellent ion-conducting function and can improve the ion conductivity of the passivation film. In addition, in the present application, there are at least two nitrogen atoms spaced apart so that the polycyclic structure formed by coupling of multiple nitrogen atoms in the additive is more stable.

[0011] In one embodiment, the oxygen atom or the sulfur atom is connected to one of the two carbon atoms. In the embodiment of the present application, the additive includes CNC=O, CNC=S, C=NC=O or C=NC=S structure, which enhances the conjugation effect between O, C, N or between S, C, N, and the conjugation effect is beneficial to improve its structural stability. When the additive is polymerized into a passivation film, there are structures such as O=CN or S=CN in the passivation film, which improves the stability of the passivation film structure. On the other hand, CNC=O, CNC=S, C=NC=O or C=NC=S structure can provide more lone pairs of electrons to make the additive easier to form a film at the positive electrode. And the nitrogen-rich passivation film component including CNC=O, CNC=S, C=NC=O or C=NC=S structure formed at the negative electrode is more conducive to ion passage and reduces the passivation film impedance.

[0012] In one embodiment, the other nitrogen atom forms a carbon-nitrogen double bond with the other of the two carbon atoms. In the embodiment of the present application, in the carbon-nitrogen double bond, the carbon-nitrogen electron cloud is unevenly distributed, biased towards the nitrogen atom, which can reduce the LUMO orbital energy of the additive molecule, making the additive more susceptible to reduction polymerization to form a passivation film on the surface of the positive and negative electrodes. At the same time, the double bond can form a passivation film of the polymerized component, improve the mechanical properties of the passivation film, and when the passivation film is formed on the surface of the negative electrode, the passivation film is not easy to break when the volume of the negative electrode shrinks during overcharge and discharge.

[0013] In one embodiment, the molecular structure of the additive includes two oxygen atoms, and the two oxygen atoms are respectively connected to the two carbon atoms, or the molecular structure of the additive includes two sulfur atoms, and the two sulfur atoms are respectively connected to the two carbon atoms, or the molecular structure of the additive includes one sulfur atom and one oxygen atom, and the one sulfur atom is connected to one of the two carbon atoms, and the one oxygen atom is connected to the other of the two carbon atoms.

[0014] In the embodiment of the present application, the additive includes O=CNC=O, S=CNC=O or S=CNC=S structure, which has a stronger conjugation effect and is beneficial to improving its structural stability. When the additive is polymerized into a passivation film, structures such as O=CNC=O, S=CNC=O or S=CNC=S exist in the passivation film, which improves the stability of the passivation film structure. On the other hand, the O=CNC=O, S=CNC=O or S=CNC=S structure can provide more lone pairs of electrons, making it easier for the additive to form a film at the positive electrode. And the nitrogen-rich passivation film component including O=CNC=O, S=CNC=O or S=CNC=S structure formed at the negative electrode is more conducive to the passage of ions and reduces the impedance of the passivation film.

[0015] In one embodiment, the additive is selected from one or more compounds having structures shown in formula (I) to formula (V):

[0016]

[0017] In formula (I) to formula (V), the X atom and the Y atom are selected from oxygen atoms or sulfur atoms, and R1, R2, and R3 are selected from any one of hydrogen, substituted or unsubstituted alkyl, alkoxy, halogen, nitro, ester, and acyl.

[0018] In the present application, when the additive is selected from the compound with the structure shown above, the additive can better improve the high temperature cycle performance and low temperature performance of the battery, so that the battery can be used in a wide temperature range. Compared with the five-membered ring and the seven-membered ring, the six-membered ring is better in electrochemical structural stability. The S, O, and N atoms are adjacently connected to the double bond, and the uneven electronegativity of the molecule makes it easier for redox reactions to form a better SEI film.

[0019] In one embodiment, the additive is selected from one or more compounds having structures shown in formula (VI) and formula (VII):

[0020]

[0021] In formula (VI) and formula (VII), the X atom and the Y atom are selected from oxygen atoms or sulfur atoms, and R1 and R2 are selected from any one of hydrogen, substituted or unsubstituted alkyl, alkoxy, halogen, nitro, ester and acyl groups.

[0022] In the present application, when the additive is selected from compounds with structures shown in formula (VI) and formula (VII), the additive can better improve the high temperature cycle performance and low temperature performance of the battery, so that the battery can be used within a wide temperature range.

[0023] In one embodiment, the total number of nitrogen atoms accounts for 5%-50% of the total number of atoms in the additive molecule. In this application, by adjusting the content of nitrogen atoms, the additive can have more excellent performance to improve the high temperature cycle performance and low temperature performance of the battery.

[0024] In a second aspect, the present application provides a battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode, the negative electrode and the separator are immersed in the electrolyte, and the electrolyte comprises the additive as described above, wherein the mass percentage of the additive in the electrolyte is 0.01%-5%.

[0025] In a third aspect, the present application provides a battery pack, comprising a plurality of batteries as described above, wherein the plurality of batteries are connected in series or in parallel.

[0026] In a fourth aspect, the present application provides an energy storage system, which includes a power conversion module and a plurality of battery packs as described above, wherein the power conversion module is used to convert the direct current power output by the battery pack to power a load, or the power conversion module is used to convert the direct current or alternating current provided by an external power source to charge the battery pack. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments of the present application will be described below.

[0028] Figure 1 A schematic diagram of an energy storage system provided in an embodiment of the present application;

[0029] Figure 2 A schematic diagram of a battery provided in an embodiment of the present application;

[0030] Figure 3 The test results of the battery impedance test provided in the embodiment of the present application;

[0031] Figure 4 The test results of the scanning electron microscope test provided in Example 1 of the present application. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0033] As used herein, unless otherwise specified, "plurality" means two or more.

[0034] For ease of understanding, the English abbreviations and related technical terms involved in the embodiments of the present application are explained and described below.

[0035] LUMO: Lowest Unoccupied Molecular Orbital, lowest unoccupied molecular orbital.

[0036] HOMO: Highest Occupied Molecular Orbital, highest occupied molecular orbital.

[0037] See also Figure 1 The present application provides an energy storage system, which includes a power conversion module 2 and a plurality of battery packs 1. The power conversion module 2 is a module capable of realizing a power conversion function. Exemplarily, the power conversion module 2 can realize at least one of DC-DC conversion, AC-AC conversion, AC-DC conversion, and DC-AC conversion. The power conversion module 2 is used to connect a load 3 and an external power source 4. The external power source 4 is connected to the power conversion module 2 and charges the battery pack 1 through the power conversion module 2. The power conversion module 2 is connected to the load 3, and the battery pack 1 supplies power to the load 3 through the power conversion module 2.

[0038] The load 3 may be a power-consuming device such as a transportation vehicle, a communication base station, a household and industrial energy storage device, etc. For example, in one embodiment, the DC power output by the battery pack 1 is converted into AC power by the power conversion module 2 and then used for power consumption in daily life and production. Alternatively, the DC power output by the battery pack 1 is converted into AC-AC power and then into AC-DC power in sequence and then used for power consumption in daily life and production.

[0039] The external power source 4 may be a mains electricity source, a generator, solar energy, wind energy, a battery, etc. The power conversion module 2 may be used to receive the electric energy provided by the external power source 4 and perform power conversion on the received electric energy to charge the battery pack 1 .

[0040] In one embodiment, the external power source 4 is a power grid, the power conversion module 2 is connected to the power grid and the battery pack 1, and the power conversion module 2 converts the AC power provided by the power grid into DC power and then charges the battery pack 1. The DC power output by the battery pack 1 can also be converted into AC power by the power conversion module 2 and then fed back into the power grid.

[0041] In one embodiment, the external power source 4 is a photovoltaic module. The power conversion module 2 is connected to the photovoltaic module, and the photovoltaic module converts solar energy into electrical energy, and charges the battery pack 1 after power conversion by the power conversion module 2. The photovoltaic module can be connected to the power grid through the power conversion module 2 to connect the generated electrical energy to the grid. The photovoltaic module can also be connected to the load 3 through the power conversion module 2 to power the load 3 with the generated electrical energy.

[0042] The battery pack 1 includes a plurality of batteries, which are connected in series or in parallel. The battery, battery pack, etc. provided in the present application can also be applied to vehicles, mobile phones, and other electronic devices.

[0043] The battery includes a positive electrode, a negative electrode, a separator and an electrolyte (such as Figure 2 As shown). Among them, the positive electrode is used to provide active ions for the battery. For example, when the battery is a sodium ion battery, the active ions are sodium ions. The negative electrode can be used as a carrier of active ions and electrons during the charging and discharging process of the battery. The electrolyte infiltrates the positive electrode, the negative electrode and the diaphragm, and the electrolyte is a carrier for the transmission of active ions. The electrolyte is used to conduct active ions between the positive electrode and the negative electrode. The diaphragm is arranged between the positive electrode and the negative electrode to separate the positive electrode and the negative electrode, and the diaphragm is used to allow active ions to pass through and block electrons from passing through.

[0044] The positive and negative electrodes can reversibly deintercalate active ions to achieve energy storage and release. For example, under the drive of an external circuit, active ions are released from the positive electrode, migrate to the negative electrode through the electrolyte and the diaphragm, and the battery is charged. When an external power load 3 is connected, active ions are released from the negative electrode, migrate back to the positive electrode through the electrolyte and the diaphragm, and the battery is discharged.

[0045] Generally, the electrolyte includes an organic solvent, an electrolyte salt and an additive. The electrolyte salt and the additive are both dissolved in the organic solvent. The electrolyte salt includes at least one of a lithium salt, a sodium salt, a potassium salt, a magnesium salt, a zinc salt and an aluminum salt. Exemplarily, when the battery is a sodium ion battery, the electrolyte salt is a sodium salt. The properties of the electrolyte affect the long-term cycle, high temperature use and storage performance of the battery. Exemplarily, electrolyte oxidation and side reactions between the electrolyte and the positive and negative electrodes can cause high temperature bloating and capacity decay of the battery.

[0046] In the embodiment of the present application, an additive is added to the electrolyte, and the additive can reduce the side reaction between the electrolyte and the positive electrode or the negative electrode, thereby improving the high temperature cycle performance and low temperature performance of the battery, so that the battery can be used within a wide temperature range.

[0047] Specifically, the present application provides an electrolyte additive, the molecular structure of which includes at least one of an oxygen atom and a sulfur atom and a nitrogen-containing heterocyclic ring. The nitrogen-containing heterocyclic ring includes at least one of a carbon-nitrogen double bond and a nitrogen-nitrogen double bond. The oxygen atom is used to form a carbon-oxygen double bond with a carbon atom on the nitrogen-containing heterocyclic ring, and the sulfur atom is used to form a carbon-sulfur double bond with a carbon atom on the nitrogen-containing heterocyclic ring.

[0048] Wherein, the nitrogen-containing heterocycle is a cyclic structure. The nitrogen-containing heterocycle can be a five-membered ring, a six-membered ring or other types of rings. When the nitrogen-containing heterocycle is a six-membered ring, the number of ring atoms of the nitrogen-containing heterocycle is 6.

[0049] The nitrogen-containing heterocyclic ring includes at least two nitrogen atoms in the ring-forming atoms, and the at least two nitrogen atoms include two adjacent nitrogen atoms, and the two adjacent nitrogen atoms form a nitrogen-nitrogen single bond or a nitrogen-nitrogen double bond. That is, the nitrogen atoms participating in the ring-forming include two nitrogen atoms connected. In the nitrogen-containing heterocyclic ring, there are two nitrogen atoms in the ring that are directly connected, so that the nitrogen-containing heterocyclic ring includes at least one nitrogen-nitrogen bond.

[0050] Illustratively, in one embodiment, the nitrogen-containing heterocycle includes two nitrogen atoms, and the two nitrogen atoms are connected to form a nitrogen-nitrogen single bond or a nitrogen-nitrogen double bond. In one embodiment, the nitrogen-containing heterocycle includes four nitrogen atoms, two of which are connected to form a nitrogen-nitrogen single bond or a nitrogen-nitrogen double bond, and the other two nitrogen atoms may also be connected to form another nitrogen-nitrogen single bond or another nitrogen-nitrogen double bond.

[0051] The nitrogen-containing heterocycle includes at least one unsaturated bond, and the unsaturation degree of the nitrogen-containing heterocycle is greater than or equal to 2. There is at least one pair of adjacent ring atoms in the nitrogen-containing heterocycle connected by an unsaturated bond. Exemplarily, the nitrogen-containing heterocycle includes two nitrogen atoms connected to each other, and an unsaturated nitrogen-nitrogen double bond is formed between the two nitrogen atoms. Exemplarily, the nitrogen-containing heterocycle includes a nitrogen atom and a carbon atom connected to each other, and a carbon-nitrogen double bond is formed between the nitrogen atom and the carbon atom.

[0052] The additive further includes at least one of an oxygen atom and a sulfur atom, and the oxygen atom and / or the sulfur atom are connected to the nitrogen-containing heterocyclic ring.

[0053] In one embodiment, the additive includes an oxygen atom, which is connected to a ring-forming carbon atom in the nitrogen-containing heterocycle to form a carbon-oxygen double bond. In one embodiment, the additive includes multiple oxygen atoms, which are respectively connected to multiple carbon atoms in the nitrogen-containing heterocycle to form multiple carbon-oxygen double bonds.

[0054] In one embodiment, the additive includes a sulfur atom, which is connected to a ring-forming carbon atom in the nitrogen-containing heterocycle to form a carbon-sulfur double bond. In one embodiment, the additive includes a plurality of sulfur atoms, which are respectively connected to a plurality of carbon atoms in the nitrogen-containing heterocycle to form a plurality of carbon-sulfur double bonds.

[0055] In one embodiment, the additive includes a sulfur atom and an oxygen atom, and the sulfur atom and the oxygen atom are respectively connected to different carbon atoms in the nitrogen-containing heterocyclic ring to form a carbon-sulfur double bond and a carbon-oxygen double bond.

[0056] In the embodiments of the present application, the structural structure of the additive enables it to have film-forming properties. During the first charging process of the battery, the additive reacts with the positive electrode and the negative electrode at the solid-liquid interface to form a passivation film on the surface of the positive electrode and the negative electrode. The formation of the passivation film can reduce the side reactions of the electrolyte with the positive electrode or the negative electrode, and can inhibit the decomposition of the electrolyte, thereby improving the stability of the battery and the high-temperature cycle performance and low-temperature performance of the battery, so that the battery can be used in a wide temperature range. The structural characteristics of the additive make the passivation film formed by the additive have more excellent performance, which is beneficial to improving the overall performance of the battery.

[0057] Specifically, on the one hand, the nitrogen-containing heterocycle in the molecular structure of the additive can improve the stability of the passivation film. The connected nitrogen atoms increase the nitrogen density of the local structure of the additive, and the nitrogen atoms can provide more lone pairs of electrons to make it easier for the additive to form a film on the positive electrode. For the passivation film formed on the surface of the negative electrode, since the additive is rich in nitrogen, the passivation film formed by the additive is rich in nitrogen. For example, the passivation film includes nitrides, which improves the ion conductivity of the passivation film and reduces the impedance of the passivation film.

[0058] On the other hand, the unsaturated bonds in the molecular structure of the additive help to form a passivation film containing the polymer, thereby improving the mechanical properties of the entire passivation film. The battery is not easily broken due to gas production during the charge and discharge process, which makes the battery have good cycle performance.

[0059] On the other hand, the oxygen atom or sulfur atom has a lone pair of electrons, which can coordinate with the metal element in the positive electrode to cover the positive electrode active site, so that the passivation film formed by the additive can effectively inhibit the side reactions on the positive electrode surface. And the nitrogen atom in the nitrogen-containing heterocycle and the sulfur atom in the oxygen-containing sulfur substituent group can increase the reduction potential of the entire additive molecule, making it easier for the additive to participate in film formation. In addition, a double bond is formed between the oxygen atom or sulfur atom and the nitrogen-containing heterocycle, and the electron-deficient divalent sulfur atom has two positive potential regions. The introduction of divalent sulfur atoms will bring about changes in the molecular electron cloud, which can greatly improve the affinity of the compound, so that the additive can be directed to poison the active sites on the surface of the positive electrode of the battery, greatly inhibiting the side reactions on the positive electrode surface. The divalent oxygen atom will affect the electron cloud of the nitrogen-containing heterocycle, which can increase the reduction potential of the entire additive molecule, making it easy for the additive to participate in film formation.

[0060] In a possible implementation, the nitrogen-containing heterocycle further includes at least one of a carbon-carbon double bond, a nitrogen-nitrogen single bond, and a carbon-nitrogen single bond.

[0061] The unsaturated bond on the nitrogen-containing heterocycle includes at least one of a carbon-nitrogen double bond, a nitrogen-nitrogen double bond, and a carbon-carbon double bond. At least one carbon atom and at least two nitrogen atoms constitute the cyclic structure of the nitrogen-containing heterocycle. In one embodiment, the nitrogen-containing heterocycle may include an unsaturated bond, which may be a carbon-nitrogen double bond, a nitrogen-nitrogen double bond, or a carbon-carbon double bond.

[0062] In one embodiment, the nitrogen-containing heterocyclic ring includes a plurality of unsaturated bonds, and the plurality of unsaturated bonds can be selected from different types of unsaturated bonds. Exemplarily, the nitrogen-containing heterocyclic ring includes a carbon-nitrogen double bond and a carbon-carbon double bond.

[0063] In one embodiment, the nitrogen-containing heterocyclic ring includes multiple unsaturated bonds, and the multiple unsaturated bonds can be selected from the same type of unsaturated bonds. Exemplarily, the nitrogen-containing heterocyclic ring includes two carbon-nitrogen double bonds.

[0064] In one embodiment, the ring atoms of the nitrogen-containing heterocyclic ring include only nitrogen atoms and carbon atoms.

[0065] In the embodiment of the present application, the double bond in the nitrogen-containing heterocyclic ring can increase the electron cloud distribution. In particular, when the unsaturated bond includes a carbon-nitrogen double bond, the carbon-nitrogen electron cloud is unevenly distributed, biased toward the nitrogen atom, and the LUMO orbital energy of the additive molecule can be reduced, making the additive more likely to undergo reduction polymerization to form a passivation film on the surface of the positive and negative electrodes. At the same time, double bonds such as carbon-nitrogen double bonds, nitrogen-nitrogen double bonds, and carbon-carbon double bonds can form a passivation film of the polymer component, which improves the mechanical properties of the passivation film. When the passivation film is formed on the surface of the negative electrode, the volume of the negative electrode shrinks during overcharge during charge and discharge, and the passivation film is not easy to break. In addition, the formation of nitrogen-nitrogen single bonds and carbon-nitrogen single bonds increases the nitrogen density of the local structure of the additive, and nitrogen atoms can provide more lone pairs of electrons to make the additive easier to form a film at the positive electrode. For the passivation film formed on the surface of the negative electrode, since the additive is rich in nitrogen, the passivation film formed by the additive is rich in nitrogen. For example, the passivation film includes nitrides, which increases the ion conductivity of the passivation film and reduces the impedance of the passivation film.

[0066] In a possible implementation, the nitrogen atom in the carbon-nitrogen double bond or the nitrogen-nitrogen double bond is selected from one of the two connected nitrogen atoms. Among them, one of the two connected nitrogen atoms in the nitrogen-containing heterocycle forms a carbon-nitrogen double bond or a nitrogen-nitrogen double bond with its adjacent carbon atom or nitrogen atom.

[0067] In one embodiment, the nitrogen-containing heterocycle includes a nitrogen-nitrogen double bond, and one nitrogen atom forming the nitrogen-nitrogen double bond is selected from one of the two nitrogen atoms connected in the nitrogen-containing heterocycle as described above, or the two nitrogen atoms forming the nitrogen-nitrogen double bond are the two nitrogen atoms connected as described above.

[0068] In one embodiment, the nitrogen-containing heterocyclic ring includes a carbon-nitrogen double bond, and one nitrogen atom forming the carbon-nitrogen double bond is selected from one of the two nitrogen atoms connected as described above.

[0069] In one embodiment, the nitrogen-containing heterocycle includes a nitrogen-nitrogen double bond and a carbon-nitrogen double bond, wherein one or two nitrogen atoms in the nitrogen-nitrogen double bond are selected from one or two of the two nitrogen atoms connected as described above, and the nitrogen atom in the carbon-nitrogen double bond is selected from the nitrogen atom on the nitrogen-containing heterocycle other than the two nitrogen atoms connected as described above.

[0070] In one embodiment, the nitrogen-containing heterocycle includes a nitrogen-nitrogen double bond and a carbon-nitrogen double bond, wherein the nitrogen atom in the carbon-nitrogen double bond is selected from one of the two nitrogen atoms connected as described above, and the nitrogen atom in the nitrogen-nitrogen double bond is selected from two nitrogen atoms on the nitrogen-containing heterocycle other than the two nitrogen atoms connected as described above.

[0071] In one embodiment, the nitrogen-containing heterocycle includes a nitrogen-nitrogen double bond and a carbon-nitrogen double bond, wherein the nitrogen atom in the carbon-nitrogen double bond is selected from one of the two nitrogen atoms connected as described above, and one of the nitrogen atoms in the nitrogen-nitrogen double bond is selected from the other of the two nitrogen atoms connected as described above.

[0072] In the embodiment of the present application, since one or both of the two nitrogen atoms connected in the nitrogen-containing heterocycle are connected with a double bond, the electrons on the double bond and the lone pair of electrons on the nitrogen atom will produce a conjugated effect. The conjugated effect is beneficial to improve its structural stability. When the additive is polymerized into a passivation film, the double bond can be polymerized into a film to form an SEI film with a polymer component, thereby improving the flexibility of the SEI film, thereby inhibiting the rupture of the SEI film during the long cycle of the battery cell, thereby greatly improving the cycle performance of the battery. On the other hand, the nitrogen-nitrogen atoms are connected to each other and the nitrogen atoms are connected with double bonds. For the positive electrode, more lone pairs of electrons can be provided to make the additive easier to form a film at the positive electrode. For the negative electrode film formation, the formation of a nitrogen-rich passivation film component is more conducive to the passage of ions and reduces the impedance of the passivation film.

[0073] In a possible implementation, the nitrogen-containing heterocycle includes three nitrogen atoms, two of the three nitrogen atoms are connected to form a nitrogen-nitrogen single bond, and another of the three nitrogen atoms is connected to two carbon atoms. The other of the three nitrogen atoms is spaced apart from the two connected nitrogen atoms. The other of the three nitrogen atoms is connected to the two connected nitrogen atoms through one or more carbon atoms.

[0074] In the embodiment of the present application, the nitrogen atom has a high electronegativity (3.04). When the additive forms a passivation film, the nitrogen atom can form a nitride with a metal with a low electronegativity such as Li, Na, etc. The nitride has an excellent ion-conducting function and can improve the ion conductivity of the passivation film. In addition, in the present application, at least two nitrogen atoms are arranged at intervals, so that the multi-ring structure formed by coupling multiple nitrogen atoms in the additive is more stable.

[0075] In a possible implementation, the oxygen atom or the sulfur atom is connected to one of the two carbon atoms, that is, another nitrogen atom among the three nitrogen atoms is connected to two carbon atoms, one of which is also connected to an oxygen atom or a sulfur atom, forming a CNC=O, CNC=S, C=NC=O or C=NC=S structure.

[0076] In the embodiment of the present application, the additive includes CNC=O, CNC=S, C=NC=O or C=NC=S structure, which enhances the conjugation effect between O, C, N or between S, C, N, and the conjugation effect is beneficial to improve its structural stability. When the additive is polymerized into a passivation film, structures such as O=CN or S=CN exist in the passivation film, which improves the stability of the passivation film structure. On the other hand, the CNC=O, CNC=S, C=NC=O or C=NC=S structure can provide more lone pairs of electrons, making it easier for the additive to form a film at the positive electrode. And the nitrogen-rich passivation film component including CNC=O, CNC=S, C=NC=O or C=NC=S structure formed at the negative electrode is more conducive to the passage of ions and reduces the impedance of the passivation film.

[0077] In one possible implementation, another nitrogen atom among the three nitrogen atoms forms a carbon-nitrogen double bond with another one of the two carbon atoms. That is, another nitrogen atom among the three nitrogen atoms is connected to two carbon atoms, and the nitrogen atom forms a carbon-nitrogen double bond with one of the carbon atoms, that is, a CN=C structure. In the embodiment of the present application, in the carbon-nitrogen double bond, the carbon-nitrogen electron cloud is unevenly distributed, biased toward the nitrogen atom, which can reduce the LUMO orbital energy of the additive molecule, making it easier for the additive to undergo reduction polymerization to form a passivation film on the surface of the positive and negative electrodes. At the same time, the double bond can form a passivation film of the polymerized component, improve the mechanical properties of the passivation film, and when the passivation film is formed on the surface of the negative electrode, the passivation film is not easy to break when the volume of the negative electrode shrinks during overcharge and discharge.

[0078] In a possible implementation, the molecular structure of the additive includes two oxygen atoms, and the two oxygen atoms are respectively connected to the two carbon atoms. The two carbon atoms are two carbon atoms connected to another nitrogen atom among the three nitrogen atoms. The two oxygen atoms and the two carbon atoms form an O=CNC=O structure.

[0079] In one embodiment, the molecular structure of the additive includes two sulfur atoms, and the two sulfur atoms are respectively connected to the two carbon atoms. The two carbon atoms are two carbon atoms connected to another nitrogen atom among the three nitrogen atoms. The two sulfur atoms and the two carbon atoms form a S=CNC=S structure.

[0080] In one embodiment, the molecular structure of the additive includes a sulfur atom and an oxygen atom, wherein the sulfur atom is connected to one of the two carbon atoms, and the oxygen atom is connected to the other of the two carbon atoms. The two carbon atoms are two carbon atoms connected to another nitrogen atom of the three nitrogen atoms. The sulfur atom, the oxygen atom and the two carbon atoms form a S=CNC=O structure.

[0081] The nitrogen-containing heterocyclic ring includes three or more nitrogen atoms, wherein two nitrogen atoms are adjacently connected, and there is a nitrogen atom separated from the two nitrogen atoms, and the nitrogen atom is connected to two carbon atoms on the nitrogen-containing heterocyclic ring, i.e., a CNC structure is formed. The two carbon atoms are connected to oxygen atoms or sulfur atoms, i.e., an O=CNC=O, S=CNC=O or S=CNC=S structure is formed.

[0082] In the embodiment of the present application, the additive includes O=CNC=O, S=CNC=O or S=CNC=S structure, which has a stronger conjugation effect and is beneficial to improving its structural stability. When the additive is polymerized into a passivation film, structures such as O=CNC=O, S=CNC=O or S=CNC=S exist in the passivation film, which improves the stability of the passivation film structure. On the other hand, the O=CNC=O, S=CNC=O or S=CNC=S structure can provide more lone pairs of electrons, making it easier for the additive to form a film at the positive electrode. And the nitrogen-rich passivation film component including O=CNC=O, S=CNC=O or S=CNC=S structure formed at the negative electrode is more conducive to the passage of ions and reduces the impedance of the passivation film.

[0083] In one possible implementation, the nitrogen-containing heterocycle includes a carbon atom, the carbon atom is connected to one or two of the three nitrogen atoms, and an oxygen atom or a sulfur atom is connected to the carbon atom to form a carbon-oxygen double bond or a carbon-sulfur double bond. Wherein, the nitrogen-containing heterocycle includes a plurality of carbon atoms, among which there is a carbon atom adjacent to the nitrogen atom on the nitrogen-containing heterocycle, and the carbon atom is connected to the oxygen atom or the sulfur atom. In one embodiment, the nitrogen-containing heterocycle also includes more carbon atoms adjacent to the nitrogen atom, and the carbon atom may also be connected to an oxygen atom or a sulfur atom.

[0084] In the embodiments of the present application, the additive includes an O=CN or S=CN structure, which enhances the conjugation effect between O, C, N or between S, C, N, and the conjugation effect is beneficial to improving its structural stability. When the additive is polymerized into a passivation film, structures such as O=CN or S=CN exist in the passivation film, which improves the stability of the passivation film structure. On the other hand, the O=CN or S=CN structure can provide more lone pairs of electrons, making it easier for the additive to form a film at the positive electrode. And the nitrogen-rich passivation film component including the O=CN or S=CN structure formed at the negative electrode is more conducive to the passage of ions, reducing the impedance of the passivation film.

[0085] In one embodiment, the nitrogen-containing heterocyclic ring may include three or more nitrogen atoms.

[0086] In a possible implementation, the molecular structure of the additive includes at least one sulfur atom, and the at least one sulfur atom forms a sulfur-carbon bond with the carbon on the nitrogen-containing heterocycle. In the additive, at least one sulfur atom forms a sulfur-carbon bond with the nitrogen-containing heterocycle.

[0087] In the embodiments of the present application, compared with oxygen atoms, the introduction of sulfur atoms will bring about changes in the molecular electron cloud, which can greatly improve the affinity of the compound, so that the additive can directionally poison the active sites on the surface of the positive electrode of the battery, greatly inhibiting the side reactions on the surface of the positive electrode. In the present application, sulfur atoms are selected to connect nitrogen-containing heterocycles, which can effectively improve the stability of the battery and the high-temperature cycle performance of the battery.

[0088] In a possible implementation, the additive is selected from one or more compounds having structures shown in formula (I) to formula (V):

[0089]

[0090] In formula (I), the X atom and the Y atom are selected from oxygen atom or sulfur atom, and R1, R2, and R3 are selected from any one of hydrogen, substituted or unsubstituted alkyl, alkoxy, halogen, nitro, ester, and acyl.

[0091] Exemplarily, the molecular structure of the additive may be:

[0092]

[0093] In the present application, when the additive is selected from the compounds of structures shown in formula (I) to formula (VII) and compounds ATUC, ATTI, and AUC, the additive can better improve the high temperature cycle performance and low temperature performance of the battery, so that the battery can be used in a wide temperature range. Compared with the five-membered ring and the seven-membered ring, the six-membered ring is better in electrochemical structural stability. The S, O, and N atoms are adjacently connected to the double bond, and the uneven electronegativity of the molecule makes it easier to undergo redox reactions to form a better SEI film.

[0094] In a possible implementation, the additive is selected from one or more compounds having structures shown in formula (VI) and formula (VII):

[0095]

[0096] In formula (VI) and formula (VII), the X atom and the Y atom are selected from oxygen atoms or sulfur atoms, and R1 and R2 are selected from any one of hydrogen, substituted or unsubstituted alkyl, alkoxy, halogen, nitro, ester and acyl groups.

[0097] In the present application, when the additive is selected from compounds with structures shown in formula (VI) and formula (VII), the additive can better improve the high temperature cycle performance and low temperature performance of the battery, so that the battery can be used within a wide temperature range.

[0098] In one possible implementation, the total number of nitrogen atoms accounts for 5%-50% of the total number of atoms in the additive molecule. Among them, nitrogen atoms can increase the reduction potential of the entire additive molecule, making it easier for the additive to participate in film formation. When the additive participates in the formation of a passivation film on the surface of the negative electrode, the nitrogen atoms in the additive can form nitrides with metals with lower electronegativity such as Li and Na. Nitrides have excellent ion-conducting functions, which can increase the ion conductivity of the passivation film and reduce the impedance of the passivation film. In addition, nitrogen atoms have lone pairs of electrons, which can coordinate with metal elements in the positive electrode to cover the active sites of the positive electrode, so that the passivation film formed by the additive can effectively inhibit side reactions on the surface of the positive electrode. In this application, by regulating the content of nitrogen atoms, the additive can have more excellent performance to improve the high temperature cycle performance and low temperature performance of the battery.

[0099] In one possible implementation, the total number of nitrogen atoms accounts for 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50% of the total number of atoms in the additive molecule.

[0100] In a possible implementation, the mass percentage of the additive in the electrolyte is 0.01%-5%. In the implementation of the present application, the addition of a relatively low content of the electrolyte additive can effectively improve the high temperature cycle performance and low temperature performance of the battery. At the same time, the addition of a relatively low content of the electrolyte additive can ensure that the viscosity of the electrolyte is not too high, reducing the negative impact of the additive on the battery performance.

[0101] In a possible implementation, the mass percentage of the liquid additive in the electrolyte may be 0.01%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%.

[0102] In order to illustrate the beneficial effects of the method of the present application, the present application also provides the following examples and comparative examples:

[0103] Example 1

[0104] Example 1 provides a battery, wherein the additive of the electrolyte in the battery is ATUC, and ATUC accounts for 0.1 wt % of the electrolyte.

[0105] Example 2

[0106] Example 2 provides a battery, which is different from Example 1 in that, in Example 2, ATUC accounts for 0.2 wt % of the electrolyte.

[0107] Example 3

[0108] Example 3 provides a battery, which is different from Example 1 in that, in Example 3, the additive is AUC, and AUC accounts for 0.3 wt % of the electrolyte.

[0109] Example 4

[0110] Example 4 provides a battery, which is different from Example 1 in that, in Example 4, the additive is ATTI, and ATTI accounts for 0.2 wt % of the electrolyte.

[0111] Example 5

[0112] Example 5 provides a battery, which is different from Example 1 in that, in Example 5, the additive is AUC, and AUC accounts for 0.2 wt % of the electrolyte.

[0113] Example 6

[0114] Example 6 provides a battery, which is different from Example 1 in that, in Example 6, the electrolyte further includes VC (ethylene carbonate), and VC accounts for 1wt% of the electrolyte.

[0115] Example 7

[0116] Example 7 provides a battery, which is different from Example 1 in that, in Example 7, the electrolyte further includes NaPO2F2 (sodium difluorophosphate), and NaPO2F2 accounts for 0.5wt% of the electrolyte.

[0117] Comparative Example 1

[0118] Comparative Example 1 provides a battery, which is different from Example 1 in that, in Comparative Example 1, the electrolyte does not contain 0.1 wt % ATUC.

[0119] Comparative Example 2

[0120] Comparative Example 2 provides a battery, which is different from Example 1 in that, in Comparative Example 2, the content of ATUC in the electrolyte is 0.009 wt %.

[0121] Comparative Example 3

[0122] Comparative Example 3 provides a battery, which is different from Example 1 in that, in Comparative Example 3, the content of ATUC in the electrolyte is 5.1 wt %.

[0123] Comparative Example 4

[0124] Comparative Example 4 provides a battery, which is different from Example 1 in that, in Comparative Example 4, the electrolyte does not contain 0.1 wt % ATUC, and the electrolyte includes 1 wt % PS (1,3-propane sultone).

[0125] Comparative Example 5

[0126] Comparative Example 5 provides a battery, which is different from Example 2 in that, in Comparative Example 5, ATUC in the electrolyte is replaced with a compound shown below with a content of 0.2 wt %:

[0127]

[0128] Comparative Example 6

[0129] Comparative Example 6 provides a battery, which is different from Example 2 in that, in Comparative Example 6, ATUC in the electrolyte is replaced with a compound shown below with a content of 0.2 wt %:

[0130]

[0131] The above embodiments and comparative examples can be prepared into batteries, such as sodium ion batteries, by the following method:

[0132] (1) Preparation of positive electrode

[0133] NaNi1 / 3Fe1 / 3Mn1 / 3O2 (also NaxCoO2, NaxMnO2, NaFePO4, NaCoPO4, NaVPO4 and other positive electrode materials), Super-P (conductive carbon black), carbon nanotubes CNT, binder PVDF (polyvinylidene fluoride) are mixed and dispersed in an organic solvent NMP (N-methylpyrrolidone) at a mass ratio of 96:1.7:0.3:2 to obtain a uniform and stable positive electrode slurry, which is evenly coated on a 12μm thick aluminum foil. The positive electrode sheet is then transferred to a tunnel oven at 90-120°C and baked for a total of 6 hours, and then rolled, slit, and die-cut to form a positive electrode sheet.

[0134] (2) Negative electrode preparation

[0135] Soft carbon (hard carbon), Super-P (conductive carbon black), SBR (styrene-butadiene rubber) and CMC (sodium carboxymethyl cellulose) are mixed in a mass ratio of 95.6:0.6:2:1.8 and dispersed in deionized water. A vacuum mixer is used to stir the mixture into a uniform negative electrode slurry, and the negative electrode slurry is evenly coated on an aluminum foil with a thickness of 12 μm. The negative electrode sheet is then transferred to a tunnel oven at 90-120°C and baked for a total of 6 hours, and then rolled, slit and die-cut to form a negative electrode sheet.

[0136] (3) Preparation of electrolyte

[0137] NaPF6 (sodium hexafluorophosphate), PC (methyl propylene carbonate): EMC (methyl ethyl carbonate): DEC (diethyl carbonate) = 35:60:5, FEC (fluoroethylene carbonate) are mixed to obtain an electrolyte. Among them, the concentration of NaPF6 is 0.9 mol / L, and FEC accounts for 2% of the total electrolyte mass. Additives are then added.

[0138] (4) Preparation of sodium ion batteries

[0139] The positive electrode sheet, the negative electrode sheet and the separator are wound or stacked to obtain a pole core, which is placed in an aluminum-plastic film packaging shell and baked at 95°C for 48 hours. The above-mentioned electrolyte is injected and sealed, and the corresponding sodium ion battery is obtained through the processes of standing, formation, aging, and capacity separation.

[0140] Related performance tests

[0141] (1) Cycle test: At 45°C, take 6 sodium ion batteries after capacity division, record the thickness of the battery before the cycle as d0, then charge at 0.5C constant current to 4.0V, switch to constant voltage cutoff current 0.05C, and then discharge at 1C to 2V, record the discharge capacity Q0, repeat the cycle 800 times, after the 800th cycle, the battery thickness is d800, and the discharge capacity is Q800. Then the thickness expansion rate (%) = (d800-d0) / d0*100%, the capacity retention rate (%) = Q800 / Q0*100%, the above results take the average value of the 6 sodium ion battery tests as the final result. The cycle test at room temperature 25°C is similar.

[0142] (2) Low temperature test: Take 4 sodium ion batteries after capacity division, charge them at 0.5C constant current to 4.0V at 25℃, and then switch to constant voltage cut-off current 0.05C, with a charging capacity of Q1. After standing in a low temperature box at -40℃ for 24h, discharge them at 0.1C to obtain a discharge capacity of Q2. The low temperature discharge retention rate (%) = Q2 / Q1*100%. The test methods for low temperature discharge retention rates at -20 and -10℃ are similar.

[0143] (3) Battery impedance test.

[0144] (4) Scanning electron microscopy test.

[0145] Performance Test Results

[0146] (1) The test results of cycle retention rate, expansion rate, and low-temperature discharge capacity retention rate are shown in Table 1:

[0147] Table 1 Test results of cycle retention rate, expansion rate, and low-temperature discharge capacity retention rate

[0148]

[0149]

[0150] It can be seen from Table 1 and in combination with Examples 1-7 and Comparative Examples 1-6 that the addition of the electrolyte additive of the present application can improve the cycle performance of the sodium ion battery, especially the high-temperature cycle performance. The reason is that the electrolyte additive of the present application has a reasonable structural design for the shortcomings of the high specific surface area of ​​the negative electrode of the sodium ion battery and the larger sodium ion radius and poorer dynamics. The additive forms a dense, elastic and low-impedance passivation film (SEI film), and synergizes with the solvent molecules in the electrolyte, preferentially covering the positive and negative electrode surfaces, effectively inhibiting the side reactions of each interface of the sodium ion battery, and reducing the battery gas production during high-temperature cycles, so that the high-temperature cycle expansion rate is greatly reduced. At the same time, the low-temperature performance is also significantly improved. Therefore, the sodium ion battery of the present application exhibits very excellent electrical properties under a wide temperature range.

[0151] It can be seen from Comparative Examples 2 and 3 that when the additive content is too small or too large, the additive has little effect on the performance of the battery. The reason is that when the content is low, the film-forming ability is insufficient, and when the content is too high, the battery impedance is too large.

[0152] It can be seen from Example 2 and Comparative Examples 5-6 that the two nitrogen atoms on the ring in the additive structure of Comparative Examples 5-6 are spaced apart, while in Example 2, there are two connected nitrogen atoms on the nitrogen-containing heterocyclic ring to form a nitrogen-nitrogen single bond. The cycle retention rate, expansion rate and low-temperature discharge capacity retention rate of the battery in Example 2 are significantly higher than those of Comparative Examples 5-6. This shows that the effect of using the electrolyte additive in this application is better than the PS commonly used in the industry, and is also better than the six-membered ring structure additive in which the nitrogen atoms are not adjacently connected.

[0153] Examples 6 and 7 illustrate that the additives of the present application can be used in combination with commonly used additives in the industry, such as VC (ethylene carbonate) and NaPO2F2 (sodium difluorophosphate). The electrolyte additives provided in the present application can also be used in combination with other commonly used additives such as PS (1,3-propane sultone), DTD (ethylene sulfate), PST (1,3-propylene sultone), TMSB (tris(trimethylsilane) borate), TMSP (tris(trimethylsilane) phosphate), TPP (tripropynyl phosphate), triallyl isocyanurate (TAIC), nitrile, siloxane, ionic additives NaDFOB (sodium difluorooxalate borate), NaFSI (sodium bis(fluorosulfonyl)imide), NaBOB (sodium bis(oxalate borate), NaBF4 (sodium tetrafluoroborate), etc., in different contents to obtain better results.

[0154] (2) The test results of the battery impedance test are as follows Figure 3 shown.

[0155] Figure 3 It can be seen that the battery impedance in Example 1 is lower, indicating that the electrolyte additive of the present application can reduce the battery impedance, and is significantly lower than the high-temperature improvement additive PS commonly used in the industry.

[0156] (3) The test results of the scanning electron microscope test of Example 1 are as follows Figure 4 shown.

[0157] Figure 4 It can be seen that the surface of the negative electrode in Example 1 is evenly covered with the passivation film, and the passivation film can effectively protect the electrode.

[0158] The electrolyte additive, battery, battery pack and energy storage system provided in the embodiments of the present application are introduced in detail above. Specific examples are used in this article to illustrate the principles and embodiments of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of ​​the present application, there will be changes in the specific embodiments and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. An electrolyte additive, characterized in that: The molecular structure of the additive includes at least one of an oxygen atom and a sulfur atom, and a nitrogen-containing heterocyclic ring, wherein the nitrogen-containing heterocyclic ring includes at least one of a carbon-nitrogen double bond and a nitrogen-nitrogen double bond; The oxygen atom forms a carbon-oxygen double bond with the carbon atom on the nitrogen-containing heterocyclic ring, and the sulfur atom forms a carbon-sulfur double bond with the carbon atom on the nitrogen-containing heterocyclic ring.

2. The electrolyte additive according to claim 1, characterized in that: The nitrogen-containing heterocyclic ring further includes at least one of a carbon-carbon double bond, a nitrogen-nitrogen single bond, and a carbon-nitrogen single bond.

3. The electrolyte additive according to claim 1, characterized in that: The nitrogen-containing heterocyclic ring includes three nitrogen atoms, two of which are connected to form a nitrogen-nitrogen single bond, and another of which is connected to two carbon atoms.

4. The electrolyte additive according to claim 3, characterized in that: The oxygen atom or the sulfur atom is bonded to one of the two carbon atoms.

5. The electrolyte additive according to claim 3, characterized in that: The other nitrogen atom forms a carbon-nitrogen double bond with the other of the two carbon atoms.

6. The electrolyte additive according to claim 3, characterized in that: The molecular structure of the additive includes two oxygen atoms, and the two oxygen atoms are respectively connected to the two carbon atoms; or The molecular structure of the additive includes two sulfur atoms, and the two sulfur atoms are respectively connected to the two carbon atoms; or The molecular structure of the additive includes a sulfur atom and an oxygen atom, the sulfur atom is connected to one of the two carbon atoms, and the oxygen atom is connected to the other of the two carbon atoms.

7. The electrolyte additive according to claim 1, characterized in that: The additive is selected from one or more compounds having structures shown in formula (I) to formula (V): In formula (I) to formula (V), the X atom and the Y atom are selected from oxygen atoms or sulfur atoms, and R1, R2, and R3 are selected from any one of hydrogen, substituted or unsubstituted alkyl, alkoxy, halogen, nitro, ester, and acyl.

8. The electrolyte additive according to claim 1, characterized in that: The additive is selected from one or more compounds having structures shown in formula (VI) and formula (VII): In formula (VI) and formula (VII), the X atom and the Y atom are selected from oxygen atoms or sulfur atoms, and R1 and R2 are selected from any one of hydrogen, substituted or unsubstituted alkyl, alkoxy, halogen, nitro, ester and acyl groups.

9. The electrolyte additive according to claim 1, characterized in that: The percentage of the total number of nitrogen atoms to the total number of atoms of the additive molecule is 5%-50%.

10. A battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode, the negative electrode and the separator are immersed in the electrolyte, and the electrolyte comprises the additive according to any one of claims 1 to 9, wherein the mass percentage of the additive in the electrolyte is 0.01% to 5%.

11. A battery pack, characterized in that: The battery pack includes a plurality of batteries as claimed in claim 10, and the plurality of batteries are connected in series or in parallel.

12. An energy storage system, characterized in that: It comprises a power conversion module and a plurality of battery packs as described in claim 11, wherein the power conversion module is used to convert the direct current output by the battery pack to power a load, or the power conversion module is used to convert the direct current or alternating current provided by an external power source to charge the battery pack.

Images