A lithium supplement electrolyte, lithium supplement positive electrode sheet and lithium ion battery

Abstract

The present application relates to the field of lithium ion batteries, and provides a lithium supplement electrolyte, a lithium supplement electrode and a lithium ion battery, all of which comprise a lithium supplement additive; the oxidation of the lithium supplement additive nitrite in the charging process can make lithium ions in the battery insert into the negative electrode, supplement the lithium ions lost in the lithium ion battery due to the formation of a solid electrolyte interface film, and improve the cycle life and capacity of the battery; in addition, the nitrate produced by the decomposition of the nitrite can improve the structure of the solid electrolyte interface film generated subsequently, which is beneficial to improve the cycle life and stability of the battery; in addition, the nitrite of the present application can be produced on a large scale and is cheap, and therefore can be applied to industrial production. Compared with the prior art, the present application has the advantages of improving the cycle life and capacity of the battery and being applicable to industrial production.

Description

Technical Field

[0001] This invention relates to the field of lithium batteries, and in particular to a lithium-replenishing electrolyte, a lithium-replenishing positive electrode, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries (LIBs) have become one of the most widely used electrochemical energy storage systems due to their high energy density, high operating voltage, and lack of memory effect. However, during the first charge of a lithium-ion battery, the organic electrolyte undergoes reduction and decomposition on the surface of the negative electrode, such as graphite, forming a solid electrolyte interphase (SEI) film. This permanently consumes a large amount of lithium from the positive electrode, resulting in a low coulombic efficiency (ICE) for the first cycle and reducing the capacity and energy density of the lithium-ion battery.

[0003] To address this problem, researchers have studied "lithium replenishment" technology. Lithium replenishment refers to adding a lithium source to the battery before it begins operation to replenish lithium ions. This replenishment works by adding lithium to the electrode materials, offsetting the irreversible lithium loss caused by the formation of the SEI film, thereby increasing the battery's overall capacity and energy density. Current lithium replenishment technologies mainly include negative electrode lithium replenishment, positive electrode lithium replenishment, and methods that involve adding additives to the positive electrode, negative electrode, or electrolyte.

[0004] Chinese patent CN116130809A discloses a method and application for lithium replenishment in the positive electrode of a lithium-ion battery. This method prepares a lithium-replenishing positive electrode sheet by mixing positive electrode active material, binder, conductive agent and positive electrode lithium replenishing agent. However, the positive electrode lithium replenishing agent in this method mainly uses lithium salt, in which nitrite is used as an electrolyte additive to promote the decomposition of the positive electrode lithium replenishing agent to replenish the lithium loss during negative electrode formation. Unlike the present invention, which directly uses nitrite as a lithium replenishing additive, the lithium salt and positive electrode active material in the electrolyte in the present invention will not be further decomposed by nitrite catalysis. At the same time, the proportion of active material in the positive electrode of the present invention is a common proportion, and its negative electrode active material capacity: positive electrode active material capacity = 1.2:1, which is within the normal range and does not require the addition of excessive lithium salt.

[0005] Chinese patent CN113258139A discloses a lithium-replenishing electrolyte comprising: a first solvent for lithium replenishment (one or more of tetrahydrofuran, diphenyl ether, tetrahydrothiophene, and methyltetrahydrofuran); a second solvent for preventing co-intercalation (one or more of propylene glycol methyl ether, glycol dimethyl ether, and diethylene glycol monomethyl ether); a lithium source (lithium acetate, lithium trifluoroacetate, and n-butyllithium) to provide lithium for SEI film formation; a third solvent (one or more of methyl ethyl carbonate, ethylene carbonate, and dimethyl carbonate) to provide the liquid environment required for lithium-ion shuttle; a lithium salt (lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, and lithium bis(oxalato)borate); and additives (ethyleneene carbonate and / or fluoroethylene carbonate). While this electrolyte can improve the initial coulombic efficiency and cycle life of lithium-ion batteries, the organic salts used are expensive and difficult to use in industrial production. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art by directly using nitrite as a lithium supplementation additive, and to provide a lithium supplementation electrolyte, lithium supplementation positive electrode sheet and lithium-ion battery that can improve battery cycle life and capacity and can be applied to industrial production.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A lithium-replenishing electrolyte, comprising the following components by mass fraction:

[0009] Lithium supplementation additive 0.5% to 2.5%;

[0010] Film-forming protective additives: 27% to 31%;

[0011] Lithium salts: 19% to 20%;

[0012] The remainder is solvent.

[0013] The lithium-supplementing additive is nitrite.

[0014] Furthermore, the nitrite includes one or more of potassium nitrite, sodium nitrite, and lithium nitrite.

[0015] Furthermore, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonate)imide, and lithium bis(fluorosulfonylimide).

[0016] Furthermore, the film-forming protective additive includes one or more of vinylene carbonate, ethylene carbonate, and fluoroethylene carbonate.

[0017] Furthermore, the solvent includes one or more of ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, and ethylene carbonate.

[0018] A lithium-supplemented positive electrode sheet, comprising the following components by mass fraction:

[0019]

[0020]

[0021] The lithium-supplementing additive is nitrite.

[0022] Furthermore, the conductive agent includes carbon black, conductive graphite, or carbon fiber.

[0023] Furthermore, the adhesive includes polyvinylidene fluoride (PVDF), polyacrylic acid, or polyimide.

[0024] A lithium-ion battery comprising a lithium-added electrolyte as described above and / or a lithium-added positive electrode as described above.

[0025] Furthermore, the negative electrode material of the lithium-ion battery is graphite.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] (1) Nitrite can be used directly as a lithium replenishing additive to improve battery capacity and cycle life and can be applied to industrial production: The lithium replenishing additive is nitrite. Its oxidation during the charging process can enable lithium ions in the battery to be inserted into the negative electrode, replenishing the lithium ions lost in the lithium-ion battery due to the formation of a solid electrolyte interface film, thereby improving the battery cycle life and capacity; In addition, the nitrate ions generated after the decomposition of nitrite can improve the structure of the subsequently generated solid electrolyte interface film after entering the electrolyte, which is beneficial to improving the cycle life and stability of the battery; In addition, the nitrite lithium replenishing additive of the present invention can be mass-produced and is inexpensive, so it can be applied to industrial production.

[0028] (2) Improve battery reliability: The lithium replenishing electrolyte and lithium replenishing positive electrode used in this invention use nitrite, which can avoid the safety hazards caused by using metallic lithium when replenishing lithium in the positive and negative electrodes, and can complete the lithium replenishment without affecting the performance of the positive and negative electrodes.

[0029] (3) The lithium replenishment method is simple and easy to implement: The lithium replenishment method of the present invention using lithium replenishment electrode liquid can prevent the positive electrode sheet from having holes caused by the decomposition of additives. The lithium replenishment method is simple and compatible with the battery assembly process in industrial production. It can be applied on a large scale in the assembly process of lithium-ion batteries. Attached Figure Description

[0030] Figure 1 The discharge specific capacity versus cycle number graphs are for the batteries formed with the lithium-added electrolyte in Examples 1-4 and Comparative Example 1.

[0031] Figure 2 The discharge specific capacity-cycle count diagrams are shown for the batteries formed by the lithium-added positive electrode sheets in Examples 5-8 and Comparative Example 1.

[0032] Figure 3 The discharge specific capacity-cycle count diagrams are shown for the batteries formed by the lithium-added positive electrode sheets in Examples 9-11 and Comparative Example 2.

[0033] Figure 4 The diagram shows the discharge specific capacity versus cycle number of batteries formed by the lithium-added positive electrode in Examples 12-14 and Comparative Example 2. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0035] To address the problems of existing lithium-ion electrode solutions, this invention uses nitrite directly as a lithium-ion additive in both the lithium-ion electrode solution and the positive electrode sheet. The oxidation of nitrite during charging allows lithium ions to embed into the negative electrode, replenishing the lithium ions lost in lithium-ion batteries due to the formation of a solid electrolyte interface film, thus improving battery cycle life and capacity. Furthermore, the nitrate ions produced after the decomposition of nitrite, upon entering the electrolyte, can improve the structure of the subsequently formed solid electrolyte interface film, further enhancing battery cycle life and stability. Additionally, the nitrite lithium-ion additive of this invention can be mass-produced and is inexpensive, making it suitable for industrial production.

[0036] This invention provides a lithium-replenishing electrolyte, which comprises the following components by mass fraction:

[0037] Lithium supplementation additive 0.5% to 2.5%;

[0038] Film-forming protective additives: 27% to 31%;

[0039] Lithium salts: 19% to 20%;

[0040] The remainder is solvent.

[0041] The lithium replenishing additive is nitrite: the decomposition reaction of nitrite under a certain voltage replenishes the lithium ions lost in the lithium-ion battery due to the formation of a solid electrolyte interface film. After lithium replenishment, the energy density of the battery is increased, thereby improving the cycle life of the battery.

[0042] The nitrites mentioned include one or more of potassium nitrite, sodium nitrite, and lithium nitrite.

[0043] The lithium salts described herein can provide migrating lithium ions, including one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonate)imide, and lithium bis(fluorosulfonylimide).

[0044] The aforementioned film-forming protective additives can improve the stability and dynamic performance of the solid electrolyte interface film on the surface of the negative electrode material, including one or more of vinylene carbonate, ethylene carbonate, and fluoroethylene carbonate.

[0045] The solvent provides the liquid environment required for lithium-ion shuttle, including one or more of ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, and ethylene carbonate.

[0046] The oxidation of lithium-ion additives during battery charging allows lithium ions in the electrolyte to embed into the negative electrode, achieving a lithium replenishment effect and thus extending the battery's cycle life and specific capacity.

[0047] This invention provides a lithium-supplemented positive electrode sheet, which comprises the following components by mass fraction:

[0048]

[0049]

[0050] The lithium-adding additive is nitrite. The nitrite ions in the nitrite react to generate nitric oxide, nitrogen dioxide, and nitrate ions during battery cycling. Nitric oxide and nitrogen dioxide can be removed during the venting stage of battery production, so they will not have too much adverse effect on the subsequent cycling process of the battery. Nitrate ions entering the electrolyte can be regarded as the addition of lithium nitrate, which can decompose at the negative electrode to generate lithium oxide, thereby improving the structure of the subsequently generated solid electrolyte interface film and improving the cycle life and stability of the battery.

[0051] The conductive agent is preferably carbon black.

[0052] The adhesive is preferably polyvinylidene fluoride (PVDF).

[0053] Since nitrite is the lithium-replenishing component in the lithium-replenishing additive during operation, and the lithium ions inserted into the negative electrode during charging can be provided by the electrolyte, non-lithium salt nitrites (such as sodium nitrite and potassium nitrite) can also achieve the same lithium-replenishing effect.

[0054] The present invention also provides a lithium-ion battery comprising the above-mentioned lithium-added electrolyte and / or lithium-added positive electrode.

[0055] The negative electrode material of the lithium-ion battery is graphite.

[0056] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0057] Examples 1-4

[0058] This embodiment provides a lithium-replenishing electrolyte. In this embodiment, the lithium-replenishing additive is sodium nitrite; the lithium salt is lithium bis(trifluoromethanesulfonate)imide; the film-forming protective additive is ethylene carbonate; and the solvent is dimethyl carbonate. The contents of the above components are shown in Table 1.

[0059] The lithium electrolyte is obtained by mixing the above components.

[0060] Table 1. Mass fraction (%) of different components in Examples 1-4

[0061] Lithium supplement additive lithium salts Film-forming protective additives solvent Example 1 0.5 19.9 27.5 52.1 Example 2 1 19.8 27.4 51.8 Example 3 1.9 19.7 27.2 51.2 Example 4 2.4 19.6 27 51.0

[0062] Example 5

[0063] This embodiment provides a lithium-replenishing electrolyte. The difference between this embodiment and Embodiment 3 is that the lithium-replenishing additive is potassium nitrite, and the mass fraction of each component is the same as in Embodiment 3.

[0064] Example 6

[0065] This embodiment provides a lithium-replenishing electrolyte. In this embodiment, the lithium-replenishing additive is potassium nitrite; the lithium salt is lithium bis(trifluoromethanesulfonate)imide; the film-forming protective additives are ethylene carbonate and ethylene carbonate; and the solvent is dimethyl carbonate.

[0066] The lithium electrolyte is composed of the following components by mass fraction:

[0067] Lithium bis(trifluoromethanesulfonate)imide 19.7%, potassium nitrite 1.9%, vinylene carbonate 1%, ethylene carbonate 26.8%, and dimethyl carbonate 50.6%.

[0068] Example 7

[0069] This embodiment provides a lithium-replenishing electrolyte. The difference between this embodiment and Embodiment 6 is that the mass fractions of the film-forming protective additive and the solvent are different.

[0070] The lithium electrolyte is composed of the following components by mass fraction:

[0071] Lithium bis(trifluoromethanesulfonate)imide 19.7%, potassium nitrite 1.9%, vinylene carbonate 5%, ethylene carbonate 25.4%, and dimethyl carbonate 48%.

[0072] Example 8

[0073] This embodiment provides a lithium-replenishing electrolyte, which is composed of the following components by mass fraction:

[0074] Lithium hexafluorophosphate 20%, lithium nitrite 2%, ethylene carbonate 25%, vinylene carbonate 1%, diethyl carbonate 52%.

[0075] Example 9

[0076] This embodiment provides a lithium-supplemented positive electrode sheet. In this embodiment, the lithium-supplementing additive is sodium nitrite; the positive electrode material is lithium iron phosphate; the conductive agent is carbon black; and the binder is PVDF.

[0077] The lithium-added positive electrode sheet is composed of the following components by mass fraction:

[0078] Sodium nitrite 1%, lithium iron phosphate 90%, carbon black SP 4%, PVDF 5%.

[0079] Preparation method of positive electrode sheet:

[0080] 4 wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone, and 10 wt% carbon black conductive agent and 80 wt% lithium iron phosphate positive electrode active material were added to prepare a uniformly dispersed slurry. The slurry was uniformly coated on the surface of a 16 μm aluminum foil and then transferred to a vacuum drying oven for complete drying. The resulting electrode was rolled and then punched to obtain the positive electrode sheet.

[0081] Example 10

[0082] This embodiment provides a lithium-supplemented positive electrode sheet. In this embodiment, the lithium-supplementing additive is potassium nitrite; the positive electrode material is lithium iron phosphate; the conductive agent is carbon black; and the binder is PVDF.

[0083] The lithium-added positive electrode sheet is composed of the following components by mass fraction:

[0084] Potassium nitrite 5%, lithium iron phosphate 85%, carbon black SP 4%, PVDF 5%.

[0085] Other positive electrode preparation methods are the same as in Example 9.

[0086] Example 11

[0087] This embodiment provides a lithium-supplemented positive electrode sheet. In this embodiment, the lithium-supplementing additive is sodium nitrite; the positive electrode material is lithium iron phosphate; the conductive agent is carbon black; and the binder is PVDF.

[0088] The lithium-added positive electrode sheet is composed of the following components by mass fraction:

[0089] Sodium nitrite 5%, lithium iron phosphate 80%, carbon black SP 7%, PVDF 8%.

[0090] Other positive electrode preparation methods are the same as in Example 9.

[0091] Example 12

[0092] This embodiment provides a lithium-supplemented positive electrode sheet. In this embodiment, the lithium-supplementing additive is sodium nitrite; the positive electrode material is lithium iron phosphate; the conductive agent is carbon black; and the binder is PVDF.

[0093] The lithium-added positive electrode sheet is composed of the following components by mass fraction:

[0094] Sodium nitrite 7%, lithium iron phosphate 80%, carbon black SP 6%, PVDF 7%.

[0095] Other positive electrode preparation methods are the same as in Example 9.

[0096] Example 13

[0097] This embodiment provides a lithium-supplemented positive electrode sheet. In this embodiment, the lithium-supplementing additive is potassium nitrite; the positive electrode material is lithium iron phosphate; the conductive agent is carbon black; and the binder is PVDF.

[0098] The lithium-added positive electrode sheet is composed of the following components by mass fraction:

[0099] Potassium nitrite 5%, lithium iron phosphate 80%, carbon black SP 7%, PVDF 8%.

[0100] Other positive electrode preparation methods are the same as in Example 9.

[0101] Example 14

[0102] This embodiment provides a lithium-supplemented positive electrode sheet. In this embodiment, the lithium-supplementing additive is potassium nitrite; the positive electrode material is lithium iron phosphate; the conductive agent is carbon black; and the binder is PVDF.

[0103] The lithium-added positive electrode sheet is composed of the following components by mass fraction:

[0104] Potassium nitrite 7%, lithium iron phosphate 80%, carbon black SP 6%, PVDF 7%.

[0105] Other positive electrode preparation methods are the same as in Example 9.

[0106] Comparative Example 1

[0107] This comparative example provides an electrolyte that does not contain any lithium-supplementing additives.

[0108] The electrolyte is composed of the following components by mass fraction:

[0109] Lithium bis(trifluoromethanesulfonate)imide 20%, ethylene carbonate 27.7%, dimethyl carbonate 52.3%.

[0110] Comparative Example 2

[0111] This comparative example provides a lithium-supplemented positive electrode sheet, which does not contain any lithium-supplementing additives.

[0112] The lithium-added positive electrode sheet is composed of the following components by mass fraction:

[0113] Lithium iron phosphate 80%, carbon black SP 10%, PVDF 10%.

[0114] Example 15

[0115] This embodiment provides a lithium-ion battery. The lithium-replenishing electrolyte from Examples 1-8 and Comparative Example 1 is added to a lithium-ion battery with artificial graphite as the negative electrode and lithium iron phosphate as the positive electrode. The button cell is assembled in the following order: negative electrode shell - negative electrode - separator - lithium-replenishing electrolyte - positive electrode - gasket - spring sheet - positive electrode shell. Finally, the battery is packaged using a battery packaging machine and left to stand to obtain the finished battery.

[0116] Testing Experiment: The finished battery underwent its first charge-discharge test. Specifically, it was charged at a constant current of 0.1C to 4V, and after charging, it was allowed to stand for 5 minutes. Then, it was discharged at a constant current of 0.1C to 2.5V, followed by charging at a constant current of 0.3C to 3.7V. After charging, it was allowed to stand for 5 minutes. Finally, it was discharged at a constant current of 0.3C to 2.5V, and the specific capacity of the subsequent discharge was tested. The specific capacity of the discharge is calculated as: Discharge capacity / Mass of active material on the positive electrode.

[0117] Experimental results are as follows Figure 1 and Figure 2 As shown in the figure, compared to Comparative Example 1, the battery with added lithium-replenishing electrolyte of the present invention exhibits a certain degree of improvement in discharge specific capacity, and maintains a high increase in discharge specific capacity even after multiple cycles. Therefore, the lithium replenishment method of the present invention using lithium-replenishing electrolyte can effectively replenish the active lithium lost due to the formation of a solid electrolyte interface film, thereby improving the electrical performance of lithium-ion batteries.

[0118] Example 16

[0119] This embodiment provides a lithium-ion battery. The lithium-added positive electrode sheet from Examples 9-14 and Comparative Example 2 is added to a lithium-ion battery with artificial graphite as the negative electrode. The electrolyte is specifically composed of the following components by mass fraction: lithium hexafluorophosphate 19.7%, ethylene carbonate 25.4%, dimethyl carbonate 48%, and vinylene carbonate 6.9%. The button cell is assembled in the following order: negative electrode shell - negative electrode - separator - electrolyte - lithium-added positive electrode - gasket - spring sheet - positive electrode shell. Finally, the battery is packaged using a battery packaging machine and allowed to stand to obtain the finished battery.

[0120] The finished battery was subjected to its first charge-discharge test. Specifically, it was charged at a constant current of 0.1C to 4V, and after charging, it was allowed to stand for 5 minutes. Then, it was discharged at a constant current of 0.1C to 2.5V, followed by charging at a constant current of 0.3C to 3.7V. After charging, it was allowed to stand for 5 minutes. Finally, it was discharged at a constant current of 0.3C to 2.5V, and the specific capacity of the subsequent discharge was tested. The specific capacity of the discharge is calculated as: discharge capacity / mass of the positive electrode active material.

[0121] Experimental results are as follows Figure 3 and Figure 4 As shown in the figure, compared with Comparative Example 2, the discharge specific capacity of the battery with added lithium positive electrode sheet of the present invention is also improved to a certain extent, and it can still maintain a high discharge specific capacity improvement in multiple cycles.

[0122] The nitrite lithium-replenishing additive of this invention, through oxidation during charging, allows lithium ions in the electrolyte to embed into the negative electrode, replenishing the lithium ions lost in lithium-ion batteries due to the formation of a solid electrolyte interface film, thereby improving battery cycle life and capacity. Simultaneously, the nitrate ions generated after the decomposition of nitrite ions enter the electrolyte, improving the structure of the subsequently formed solid electrolyte interface film, which is beneficial for improving battery cycle life and stability. The preparation method of this invention is simple and easy to implement, and also conducive to mass production.

[0123] It should be noted that the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the inventive concept of the present invention, and these modifications and improvements are also within the scope of protection of the present invention.

Claims

1. A lithium-supplemented positive electrode, characterized in that, The lithium-added positive electrode sheet adopts the following components according to mass fraction: Lithium supplement additives 1% to 10%; Cathode material accounts for 80% to 90%; Conductive agent 3% to 15%; Adhesive 3% to 15%, The lithium supplementation additive is one or two of potassium nitrite and sodium nitrite; The cathode material is lithium iron phosphate; The conductive agent includes carbon black, conductive graphite, or carbon fiber; The adhesives include polyvinylidene fluoride, polyacrylic acid, or polyimide.

2. A lithium-ion battery, characterized in that, Including the lithium-filled positive electrode sheet as described in claim 1.

3. The lithium-ion battery according to claim 2, characterized in that, The negative electrode material of the lithium-ion battery is graphite.

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