Nitrogen center lithium pre-intercalation agent for lithium ion battery as well as preparation method and application of nitrogen center lithium pre-intercalation agent

Abstract

The invention belongs to the technical field of lithium supplement of secondary batteries, and particularly relates to a nitrogen center lithium pre-intercalation agent for a lithium ion battery as well as a preparation method and application of the nitrogen center lithium pre-intercalation agent. The nitrogen center lithium pre-intercalation agent provided by the invention is a conjugated nitrogen heterocyclic organic lithium salt with a specific structure. The material has high specific capacity and moderate lithium removal potential, and is compatible with an electrochemical window of a mainstream positive electrode material. The lithium pre-intercalation agent is stable to water and oxygen and can be safely operated in a conventional production environment, an oxygenolysis product of the lithium pre-intercalation agent can be dissolved in an electrolyte, and the lithium pre-intercalation agent plays an additive role in improving an interface and improving cycle performance. The invention also comprises a preparation method of the lithium pre-intercalation agent, and the lithium pre-intercalation agent is applied to the positive electrode of the lithium ion battery in a doping or coating manner, so that the active lithium loss of the first cycle of the battery is compensated, and finally, the first cycle coulombic efficiency and the cycle life of the lithium ion battery are effectively improved. The problems that an existing lithium supplementing agent is poor in air stability, many in side reaction and low in safety are solved.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery lithium replenishment technology, specifically relating to nitrogen-centered pre-lithiating agents for lithium-ion batteries, their preparation methods, and applications. Background Technology

[0002] As the mainstream energy storage device, lithium-ion batteries are being actively developed with silicon-based (such as SiO2) technology to improve energy density. x High-capacity anode materials such as 4200mAh / g. However, such materials will consume a large number of active lithium ions during the first cycle due to irreversible side reactions and the formation of SEI film on the anode surface, resulting in a significant reduction in the coulombic efficiency (ICE) of the full battery in the first cycle (for example, the ICE of SiO anode is usually below 85%), causing a capacity loss of more than 15%. Although pre-lithiation technology can compensate for losses by pre-storing lithium, existing lithium replenishment agents (such as Li5FeO4, lithium metal powder) have serious defects: (1) poor compatibility with the cathode, which can easily cause side reactions in the cathode system and destroy the structural stability of the cathode material; (2) low process safety, as highly active materials are sensitive to humidity / oxygen, increasing the difficulty of production control and safety risks; (3) uncontrollable kinetics, which can easily generate gas or exotherm during the decomposition process, leading to battery expansion or thermal runaway. Especially for the cathode lithium replenishment scenario, there is currently a lack of pre-lithiation agents that have air stability, electrochemical compatibility and controllable lithium release characteristics, which has become a key bottleneck restricting the industrialization of high energy density batteries. Summary of the Invention

[0003] The purpose of this invention is to provide a nitrogen-centered pre-lithiating agent for lithium-ion batteries with high air stability, high electrochemical compatibility and controllable lithium release characteristics, as well as its preparation method and application.

[0004] The nitrogen-center pre-lithiating agent for lithium-ion batteries provided by this invention is an organic lithium salt having the following general structural formula: ; Wherein, R is selected from: cyano, alkyl with 1-10 carbon atoms, haloalkyl with 1-10 carbon atoms, chain ether with 1-10 carbon atoms, cyclic ether with 1-10 carbon atoms, chain ester with 1-10 carbon atoms, and cyclic ester with 1-10 carbon atoms.

[0005] Preferably, R is an alkyl group selected from -Me, -Et; or a haloalkyl group selected from -F, -CF3, -C2F5.

[0006] More preferably, R is unsubstituent.

[0007] The present invention also provides a method for preparing the nitrogen-center pre-lithiating agent, the specific steps of which are as follows: (1) 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxynitrile was dissolved in a solvent and recrystallized to obtain the precursor; (2) Dissolve the precursor obtained in step (1) in an organic solvent, add lithium methoxide to react, and after the reaction, extract, dry and evaporate the solvent to obtain a solid product. (3) The solid product obtained in step (2) is recrystallized using methanol and dichloromethane, and dried to obtain the pre-lithiation agent.

[0008] In steps (1) and (2), the solvent is independently selected from at least one of methanol, ethanol, and acetonitrile.

[0009] In step (2), the reaction time is 1-10 hours; In step (3), the drying is vacuum drying at 50-100℃ for 10-24 hours.

[0010] The nitrogen-centered pre-lithiated agent can be used as a cathode material for lithium-ion batteries.

[0011] The present invention also provides a lithium-ion battery cathode material, comprising a cathode active material and the aforementioned nitrogen-centered pre-lithiating agent. Specifically, the lithium-ion battery cathode material is composed of the pre-lithiating agent and the cathode active material, wherein the mass ratio of the nitrogen-centered pre-lithiating agent to the cathode active material is 5:95 to 10:90.

[0012] The lithium-ion battery cathode material, in addition to the pre-lithiating agent and the cathode active material, also includes conductive agents, binders, etc.; they are mixed to form a cathode slurry and coated onto the current collector.

[0013] The present invention also provides a lithium-ion secondary battery that uses the aforementioned positive electrode material.

[0014] In the lithium-ion secondary battery, the nitrogen-center pre-lithiating agent in the positive electrode material can be used to compensate for the irreversible capacity loss of the lithium-ion battery. Specifically, during the first charge of the battery, the pre-lithiating agent is applied at 3.8-4.3V (vs Li) + / Li 0 At a specific potential, the pre-lithiating agent undergoes electrochemical oxidation and decomposition, releasing lithium ions to compensate for irreversible capacity loss caused by the formation of the SEI film on the negative electrode. After completing its lithium replenishment function, the resulting oxidation products remain in the battery as electrolyte additives, exhibiting high chemical stability and excellent air tolerance. This allows the pre-lithiating process to be carried out safely and efficiently under normal production conditions, ultimately achieving synergistic optimization of battery energy density improvement and long-cycle capacity retention.

[0015] It can be seen that the pre-lithiating agent of the present invention achieves in-situ controllable lithium compensation during the battery preparation process.

[0016] Specifically, the pre-lithiating agent of the present invention undergoes the following reaction during the pre-lithiating process: ; As shown above, organic lithium salts operate in a balance of positive and negative ions. When negative ions lose electrons and oxidize, positive ions are released, thus replenishing lithium. This process is only related to the oxidation potential of the negative ions. Within the normal operating voltage range of lithium-ion secondary batteries, negative ions from other organic structures (such as organic sulfonates, organic carboxylates, organic pentafluorophosphates, organic trifluoroborates, and organic phenolates) cannot undergo effective oxidative decomposition because their oxidation potentials are outside this applicable range, and therefore cannot achieve the purpose of replenishing lithium to the electrodes.

[0017] Furthermore, by selecting R, the side groups of the aforementioned organic pre-lithiating agent can be adjusted, thereby allowing for the adjustment of different parameters such as the achieved voltage and product to meet the needs of different battery systems. For example, according to the above reaction formula: When R has no side groups, the pre-lithiated agent has the highest specific capacity and the lowest decomposition voltage, making it suitable for use in coating on the surface of the positive electrode or for doping inside the positive electrode.

[0018] When R is a fluoroalkyl group, the specific capacity of the pre-lithiated agent decreases and the oxidation voltage increases, but the oxidation products can help form a lithium fluoride-rich SEI interface layer, thus making it suitable for high-voltage cathodes.

[0019] From the perspective of the pre-intercalator's specific capacity, voltage, and the effect of oxidation products, it is more preferable to have no side groups.

[0020] The pre-lithiating agent of this invention achieves molecular structure design freedom by using a conjugated nitrogen heterocycle as the backbone and adjusting the side groups, and the synthesis process is simple and inexpensive. This pre-lithiating agent exhibits high specific capacity and a suitable delithiation potential, compatible with the electrochemical windows of mainstream cathode materials. The pre-lithiating agent demonstrates excellent stability in air, with no exothermic / gas generation risk during the pre-intercalation process. Oxidation products remain in the battery as electrolyte additives, improving cycle capacity retention while meeting the needs of large-scale industrial production.

[0021] This invention applies a pre-lithiated agent to prepare the positive electrode of a secondary battery through doping or coating, in order to compensate for the loss of active lithium in the first cycle of the battery, and ultimately effectively improve the first-cycle coulombic efficiency and cycle life of the lithium-ion battery. Attached Figure Description

[0022] Figure 1 This refers to the lithium-ionized 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxylon before and after lithium-ionization treatment in Example 1 of this invention. 13 C, 1 H NMR spectrum and infrared spectrum.

[0023] Figure 2The CV test curve and charge / discharge test curve of the lithium-ion 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxynitrile button cell in Example 1 of this invention are shown.

[0024] Figure 3 These are Raman and liquid phase mass spectra of the lithium-ion 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxynitrile coin cell electrolyte before and after charging in Example 1 of this invention.

[0025] Figure 4 The infrared comparison and charge-discharge test curves of the newly prepared sample of lithium-ionized 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxynitrile in Example 1 of this invention and the sample stored in air with different humidity levels are shown.

[0026] Figure 5 This is a charge-discharge curve test of pre-lithiating agents with different side group substitutions in Example 1 of the present invention. Detailed Implementation

[0027] The present invention will be further described below with reference to the embodiments and accompanying drawings. Example 1

[0028] (1) Preparation of nitrogen-center pre-lithium intercalator Take 200 mmol of commercially available 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxynitrile and add it to 50 ml of anhydrous methanol. The resulting solid powder is placed in a vacuum oven and dried under vacuum at 60-70 °C for 10 hours.

[0029] 100 mmol of 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxynitrile was added to 50 mL of anhydrous methanol and stirred until completely dissolved. Two equivalents of lithium methoxide were added, and the mixture was heated under reflux at 80 °C for 10 hours. After the reaction was complete, the solvent was evaporated to dryness.

[0030] The obtained solid was recrystallized using methanol and dichloromethane, and the resulting solid powder was dried in a vacuum oven at 100°C to obtain a pre-lithium-intercalated material. Figure 1 This refers to the lithium-ionized 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxylon before and after lithium-ionization treatment in Example 1 of this invention. 13 C, 1 H NMR spectrum and infrared spectrum.

[0031] (2) Battery preparation and testing: Lithium-1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxynitrile, PVDF, and Super P were added to a planetary ball mill in a mass ratio of 6:3:1. 3-5 grinding balls were added, and the milling speed was controlled at 250-300 rpm for 45 minutes to ensure uniform mixing of the solid powders. Then, NMP solvent was added, and the milling continued for another 45 minutes. The slurry was coated onto an aluminum foil current collector to serve as the positive electrode. The electrode was placed in a vacuum oven and dried at 100°C for at least 10 hours. In a glove box, the positive electrode shell, carbon paper, separator, lithium-ion negative electrode, gasket, spring contact, and negative electrode shell were placed sequentially. Electrolyte was added, and the cells were fixed using a battery press to assemble a coin cell.

[0032] The assembled coin cells were tested using an electrochemical workstation to measure CV curves, with a scan range of 2.5-4.3V and a scan rate of 0.1mV / s. Figure 2 As shown in Figure a, the CV curves indicate that 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxynitrile exhibits irreversible delithiation capacity. The delithiation capacity of 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxynitrile was tested using a coin cell test channel, employing constant current charging and discharging at 0.06 mA and a cutoff voltage of 2.5-4.3 V. Figure 2 As shown in b, the charge-discharge curves show that lithiated 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxynitrile has a capacity close to 300 mAh / g and a decomposition potential between 3.7 and 4.3 V, which is a suitable delithiation potential and meets the basic requirements of pre-lithiation materials.

[0033] Figure 2 a represents the CV curve test of the 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxylonite coin cell in this embodiment. It can be seen that the 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxylonite begins to decompose during charging at 3.7V, releasing lithium ions.

[0034] Figure 2 b shows the charge-discharge test results of the lithium-ion 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxylonite coin cell in this embodiment. It can be seen that the lithium-ion 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxylonite begins to decompose during charging at 3.8V and has a capacity of approximately 367mAh / g.

[0035] Figure 3The images show Raman and liquid chromatography-mass spectra of the lithium-ion 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxynitrile coin cell electrolyte before and after charging in Example 1 of this invention. After charging, a Raman peak of the cyano group can be seen, indicating that the lithium-ion 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxynitrile is oxidized and releases lithium ions during charging, and the oxidation products dissolve in the electrolyte.

[0036] Figure 4 A comparison of the infrared spectra of the freshly prepared sample of lithiated 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarboxynitrile and the sample stored in dry air in this embodiment shows that the infrared spectra of the freshly prepared sample and the sample stored in air are basically the same, and the charge-discharge curves show almost no change. This indicates that the pre-lithiated material has good chemical stability.

[0037] Figure 5 This is a charge-discharge curve of the pre-lithiating agent with different side group substitutions in Example 1 of the present invention. It is an organolithium salt having the following structure.

[0038] ; In this invention, as a pre-lithiation method, the pre-lithiation agent of this invention can be directly added to the positive electrode slurry and carried out through an electrochemical reaction of charging oxidation decomposition.

[0039] As an electrode doping method, the following approach can be used: The pre-lithiating agent described above in this invention is mixed with a desired positive electrode material, conductive agent, binder, and solvent, and then uniformly ground using a grinding mill such as an agate ball mill. Next, a coating film is formed on the electrode current collector using a coating machine, and then vacuum dried in a vacuum oven to obtain an electrode sheet containing the aforementioned conjugated nitrogen heterocyclic structure of this invention. This electrode sheet is then assembled into a pre-packaged battery, and an electrochemical reaction is performed to induce the pre-lithiating process.

[0040] As the positive / negative electrode of a lithium-ion secondary battery, a positive / negative electrode sheet with a structure having an active material layer containing a positive / negative active material and a binder formed on a current collector can be used, for example. The positive and negative current collectors of the present invention can use any material suitable for use as a current collector in a lithium-ion battery; for example, copper can be used as the negative current collector and aluminum as the positive current collector. The positive active material of the present invention can use any material suitable for use as a positive active material in a lithium-ion battery, such as ternary materials such as lithium iron phosphate, lithium cobalt oxide, and NCM811. The aforementioned positive electrode may contain a binder; as a binder, for example, any substance commonly used in the art as a positive electrode binder for lithium-ion batteries, such as polyvinylidene fluoride (PVDF), polyacrylic acid binders, or polyurethane binders, can be used.

[0041] The negative electrode active material of the present invention can use any material that can be used as a negative electrode active material for lithium-ion batteries, such as lithium metal, graphite, silicon carbide, Si or composites of these, such as composites of Si and graphite, composites of Si and lithium metal, composites of graphite and lithium metal, etc.; silicon oxide compounds such as silicon monoxide (SiO), etc.

[0042] The aforementioned active material layer may further contain a conductive agent. Examples of such conductive agents include conductive carbon Super P, carbon nanotubes (CNTs), natural graphite, artificial graphite, coke, carbon black, pyrolytic carbon, carbon fiber, calcined organic polymer compounds, and any other substances commonly used as conductive agents for lithium-ion batteries in the art.

[0043] For the pre-lithiated cathode of the present invention, pre-lithiation treatment can be carried out by electrochemical reaction of the pre-intercalating agent shown in formula (1) of the present invention through electrode doping and coating methods. The pre-lithiated electrode of the prior art requires the use of lithium metal materials, which have air instability and inconvenience of operation, and the reaction is violent and the reaction time is difficult to control, which will lead to the instability of the cathode interface and affect the battery cycle performance. The pre-lithiated material of the present invention with the above-mentioned conjugated nitrogen heterocyclic structure is stable to water and oxygen, convenient to operate, and the reaction process is mild, effectively avoiding the above problems. Based on a 1Ah battery, the traditional LFP-graphite, ternary-graphite and lithium cobalt oxide-graphite battery systems have an initial efficiency of over 95%. To achieve 100% efficiency, the amount of lithium replenishment is between 0.1% and 5%. Special battery systems with lithium-free cathode-graphite and lithium-free cathode-copper do not contain lithium ions, and the initial efficiency after 100% lithium replenishment is only about 50%. To achieve 100% efficiency, the amount of lithium replenishment is between 100% and 200%.

Claims

1. A nitrogen-centered prelithiation agent for lithium-ion batteries, characterized in that, is an organic lithium salt having the following structural formula: ； wherein R is selected from the group consisting of cyano, alkyl having 1-10 carbon atoms, haloalkyl having 1-10 carbon atoms, chain ether having 1-10 carbon atoms, cyclic ether having 1-10 carbon atoms, chain ester having 1-10 carbon atoms, and cyclic ester having 1-10 carbon atoms.

2. The nitrogen-centered prelithiation reagent of claim 1, wherein The R is selected from the group consisting of alkyl of -Me, -Et; haloalkyl of -F, -CF3, -C2F5.

3. The nitrogen-centered prelithiation reagent of claim 1, wherein The R is unsubstituted.

4. The process for the preparation of a nitrogen-centered prelithiation agent according to one of claims 1 to 3, characterized in that, The specific steps are as follows: (1) recrystallizing 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazine dicarbonitrile in a solvent to obtain a precursor; (2) dissolving the precursor obtained in step (1) in an organic solvent, adding lithium methoxide to react, and after the reaction, extracting, drying, and evaporating the solvent to obtain a solid product; (3) recrystallizing the solid product obtained in step (2) using methanol and dichloromethane, and drying to obtain the pre-lithiation agent.

5. The preparation method of claim 4, wherein: In steps (1) and (2), the solvent is independently selected from at least one of methanol, ethanol, and acetonitrile; In step (2), the reaction time is 1-10 hours; In step (3), the drying is vacuum drying at 50-100°C for 10-24 hours.

6. Use of the nitrogen-centered pre-lithiation agent of any one of claims 1-3 in the preparation of a positive electrode material of a lithium ion battery.

7. A positive electrode material for a lithium-ion battery, characterized in that, The positive electrode material comprises a positive electrode active material and the nitrogen-centered pre-lithiation agent of any one of claims 1-3; the positive electrode material is formed by compounding the nitrogen-centered pre-lithiation agent with the positive electrode active material, and the mass ratio of the nitrogen-centered pre-lithiation agent to the positive electrode active material is 5:95 to 10:

90.

8. The positive electrode material of a lithium-ion battery according to claim 7, characterized in that, It further comprises a conductive agent and a binder; the nitrogen-centered pre-lithiation agent, the positive electrode active material, and the conductive agent and the binder are mixed to form a positive electrode slurry, which is coated on a current collector.

9. A lithium-ion secondary battery characterized by comprising: The positive electrode material of a lithium ion battery as claimed in claim 7 or 8 is used.

10. The lithium-ion secondary battery as described in claim 9, characterized in that, The nitrogen center in the positive electrode material pre-embeds lithium agent to compensate for the irreversible capacity loss of lithium ion battery, and the specific compensation method is: during the first charging process of the battery, the pre-embedded lithium agent is electrochemically oxidized and decomposed at 3.8-4.3 V (vs Li + / Li 0 ) potential, releases lithium ions to compensate for the irreversible capacity loss caused by the negative electrode SEI film; after completing the lithium compensation function, the oxidation product produced by the pre-embedded lithium agent remains in the battery as an electrolyte additive, and has high chemical stability and excellent air resistance, so that the pre-embedded lithium process can be safely and efficiently carried out in the conventional production environment, and finally the synergistic optimization of battery energy density improvement and long cycle capacity retention rate is realized.

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