A positive electrode containing a composite nitrate active material for a room temperature lithium metal primary battery and a method for preparing the same

Abstract

The application discloses a room-temperature lithium metal primary battery with a positive electrode containing a lithium nitrate active substance, comprising a negative electrode, a positive electrode sheet and a non-aqueous electrolyte, wherein the positive electrode sheet comprises a current collector, a positive electrode coating coated on the current collector and a composite nitrate dispersed in the positive electrode coating in the form of solid particles; the composite nitrate is composed of lithium nitrate and at least one other metal nitrate. By coating a plurality of nitrate salts in the form of solid particles on the positive electrode, the synergistic effect between different nitrate salts is utilized, the positive electrode reaction kinetics is effectively improved, the electrochemical polarization is reduced, and the battery has a more stable discharge voltage platform and more excellent large-current discharge capacity at room temperature.

Description

Technical Field

[0001] This invention relates to the field of lithium primary battery technology, specifically to a room temperature lithium metal primary battery with a positive electrode containing a composite nitrate active material and its preparation method. Background Technology

[0002] Lithium metal primary batteries use metallic lithium as the negative electrode active material. Thanks to their extremely high theoretical specific capacity and lowest electrode potential, they possess unparalleled advantages in terms of specific energy compared to other chemical power sources. Simultaneously, lithium metal primary batteries also exhibit excellent discharge performance and ultra-long storage life, making them irreplaceable in specialized equipment fields with extremely stringent requirements for power reliability, specific energy, and storage life, such as aerospace, deep-sea exploration, emergency rescue, oil drilling, and emergency positioning.

[0003] Currently, the positive electrode active materials for room temperature lithium metal primary batteries are mainly divided into the following categories: The first category is transition metal oxides, such as manganese dioxide and vanadium pentoxide, whose specific capacity is usually between 200 and 300 mAh / g, and whose specific energy is limited; the second category is metal sulfides, such as iron disulfide, which have certain specific capacity advantages, but the preparation process of some materials is complex and the cost is high; the third category is oxyacid salts, among which lithium nitrate is considered a highly promising candidate material for positive electrode active materials due to its high theoretical capacity, low cost, and environmental friendliness.

[0004] Existing technologies involving room-temperature lithium metal primary batteries using lithium nitrate as the positive electrode active material all employ a technical approach where "lithium nitrate is dissolved in the electrolyte, and the positive electrode is merely a conductive framework." This means that lithium nitrate is completely dissolved in the electrolyte, and the positive electrode is only coated with conductive carbon material, containing no nitrate active material. This solution-based system has significant drawbacks: firstly, lithium nitrate dissolved in the electrolyte is prone to migration and loss, leading to a continuous decrease in the concentration of active material during battery discharge, resulting in poor discharge stability and rapid capacity decay; secondly, high concentrations of lithium nitrate in the electrolyte easily trigger side reactions, leading to increased battery self-discharge rate and decreased storage performance; furthermore, the utilization rate of active material in this system is low, making it difficult to fully utilize the high energy density advantage of lithium nitrate.

[0005] To address the inherent defects of the aforementioned dissolved systems, those skilled in the art have attempted to fix lithium nitrate in solid form onto the positive electrode, thus developing a single-lithium nitrate coated positive electrode technology. However, the single-lithium nitrate solid positive electrode reveals new problems during actual discharge: on the one hand, due to the extremely poor electronic conductivity of lithium nitrate particles, electrons are difficult to effectively transfer to the interior of the lithium nitrate particles during discharge, leading to voltage lag or increased polarization in the initial stage of discharge; on the other hand, the discharge products of lithium nitrate are insulating materials, and as the discharge progresses, these products continuously cover and accumulate on the surface of the lithium nitrate particles, gradually blocking electron transport channels and ion diffusion paths, causing a sharp deterioration in reaction kinetics and a continuous increase in polarization. Summary of the Invention

[0006] The present invention aims to provide a room temperature lithium metal primary battery with a positive electrode containing a composite nitrate active material and a method for preparing the same. By coating a composite nitrate containing lithium nitrate and at least one other metal nitrate as a solid active material onto the positive electrode, the synergistic effect between the multiple nitrate components is utilized to overcome the inherent defects of a single nitrate positive electrode.

[0007] To achieve the above objectives, the first aspect of this application provides the following technical solution: A room-temperature lithium metal primary battery with lithium nitrate active material in the positive electrode includes a negative electrode, a positive electrode sheet, and a non-aqueous electrolyte. The positive electrode sheet includes a current collector, a positive electrode coating coated on the current collector, and a composite nitrate dispersed in the positive electrode coating in the form of solid particles. The composite nitrate is composed of lithium nitrate and at least one other metal nitrate.

[0008] In some embodiments, the other metal nitrate is selected from one or more of sodium nitrate, potassium nitrate, rubidium nitrate, cesium nitrate, magnesium nitrate, calcium nitrate, strontium nitrate, and barium nitrate.

[0009] Furthermore, in the composite nitrate, lithium nitrate accounts for 30% to 95% by mass, and other metal nitrates account for 5% to 70% by mass.

[0010] Furthermore, the positive electrode coating comprises, by mass ratio of components: 65-95% composite nitrate, 2-25% conductive agent, and 1-10% binder.

[0011] Optimized, the conductive agent is selected from one or more of acetylene black, Super P, carbon nanotubes, graphene, and Ketjen black.

[0012] Preferably, the adhesive is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylic acid, and LA133 waterborne adhesive.

[0013] Furthermore, the non-aqueous electrolyte contains lithium salts and non-aqueous organic solvents.

[0014] Furthermore, the lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, and lithium difluorooxalate borate; the non-aqueous organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, ethylene glycol dimethyl ether, 1,3-dioxolane, and tetraethylene glycol dimethyl ether.

[0015] A second aspect of this application provides a method for preparing the primary battery described in the first aspect, comprising the following steps: S1. Preparation of composite positive electrode sheet: In a dry environment with a dew point below -40°C, lithium nitrate solid powder and at least one other metal nitrate solid powder are pre-mixed and ground in a certain proportion to obtain a composite nitrate precursor; the precursor is dispersed in a solvent with a conductive agent and a binder in a certain proportion and stirred and mixed evenly to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the surface of the current collector, and after drying, rolling and cutting, a composite positive electrode sheet is obtained; S2. Electrolyte preparation: Dissolve lithium salt in a non-aqueous organic solvent in an inert atmosphere or dry air environment, stir evenly, and a non-aqueous electrolyte is obtained. S3. Battery assembly: In an inert atmosphere or dry air environment, the prepared composite positive electrode, separator, and lithium metal negative electrode are stacked or wound in sequence, injected with the prepared non-aqueous electrolyte, sealed and left to stand to obtain a room temperature lithium metal primary battery.

[0016] Furthermore, the solvent mentioned in step S1 is N-methylpyrrolidone or deionized water.

[0017] Working principle and beneficial effects of the present invention: Compared with existing single lithium nitrate systems and other soluble systems, this invention has the following significant advantages: 1. Synergistic optimization of discharge performance: The introduced alkali metal nitrates such as sodium nitrate and potassium nitrate have higher decomposition potentials or different melting characteristics than lithium nitrate. In solid-phase reactions, they can act as a "solid solution framework" to alleviate the dense accumulation of lithium nitrate discharge products, thereby reducing electrochemical polarization, making the discharge voltage platform more stable, and increasing the median voltage.

[0018] 2. Significantly improved rate performance: For example, the introduction of nitrates with low hygroscopicity or high ionic conductivity (such as potassium nitrate and rubidium nitrate) can improve the ion transport channels between solid particles, making the capacity retention rate of the battery significantly better than that of pure lithium nitrate cathode when discharged at higher rates (such as 0.5C and 1C).

[0019] 3. Cost Control and Environmental Adaptability: The cost of bulk inorganic salts such as sodium nitrate and potassium nitrate is much lower than that of lithium nitrate. By using composite formulations, the overall cost of cathode materials can be effectively reduced. At the same time, multi-component composite salts can form eutectic mixtures, reducing the sensitivity of the cathode coating to moisture and lowering the environmental control difficulty and process cost of electrode preparation.

[0020] 4. High safety: Since the electrolyte contains no nitrate solutes, and only the positive electrode coating contains fixed nitrates, the free release of highly oxidizing nitrates in the electrolyte is avoided, which fundamentally improves the safety performance of the battery under short circuit, over-discharge or high temperature storage conditions. Attached Figure Description

[0021] Figure 1 Implementation Case 1: Discharge Curves at Different Rates Figure 2 Comparison of discharge curves at different rates in case studies Detailed Implementation The following detailed description illustrates the specific implementation method: Example 1 (LiNO3-NaNO3 composite system) (1) Preparation of composite positive electrode sheet: In a drying room with a dew point of -45 ℃, two nitrate solids were weighed at a mass ratio of LiNO3:NaNO3 = 7:3, mixed and ground for 30 minutes to obtain composite nitrate. PVDF was dissolved in NMP at a ratio of 85% composite nitrate, 10% conductive agent acetylene black, and 5% binder PVDF. Acetylene black and composite nitrate were added, and the mixture was stirred under vacuum for 4 h. The mixture was coated onto 20 μm carbon-coated aluminum foil, vacuum dried at 120 ℃ for 12 h, and then rolled and cut.

[0022] (2) Electrolyte preparation: Prepare an electrolyte solution of 1.0 M LiTFSI dissolved in DOL / DME (volume ratio 1:1) in the glove box.

[0023] (3) Battery assembly: Using lithium metal sheets as negative electrodes and Celgard 2325 as separators, CR2032 button cells are assembled.

[0024] Example 2 (LiNO3-KNO3 composite system) In Example 1, NaNO3 was replaced with KNO3, and the mass ratio of LiNO3 to KNO3 was 8:2. The remaining steps were the same as in Example 1.

[0025] Example 3 (LiNO3-Mg(NO3)2 composite system) The compound nitrate formulation was modified to 80% LiNO3 and 20% Mg(NO3)2 (anhydrous). Given that Mg(NO3)2 is highly hygroscopic, the feeding and mixing processes must be strictly operated under conditions where the dew point is below -50 °C. The remaining steps are the same as in Example 1.

[0026] Example 4 (Multi-component composite system) The composite nitrate formulation consisted of 60% LiNO3, 20% NaNO3, and 20% KNO3. The conductive agent was a mixture of carbon nanotubes (CNTs) and Super P (mass ratio 1:1), and the binder was LA133 water-based adhesive. The solvent was deionized water. The coating drying temperature was 100 °C. The remaining steps were the same as in Example 1.

[0027] Comparative Example 1 (Pure Lithium Nitrate Cathode) The positive electrode active material is pure LiNO3, and the rest of the process is the same as in Example 1.

[0028] Performance testing: At room temperature (25 ℃), the capacitor was discharged at a constant current rate of 0.2 C to 1.5 V. The discharge plateau voltage and specific capacitance were recorded. The test results are shown in the table below:

[0029] As can be seen from the data in the table above, compared with the pure lithium nitrate cathode (Comparative Example 1), the composite nitrate cathode system of the present invention (Examples 1-4), although due to the introduction of non-electrochemically active cations (such as Na+), + K + Mg 2+ This resulted in a slight decrease in specific capacity based on the total mass of the positive electrode coating, but the plateau voltage of the battery generally increased by 0.06–0.12V, and the high-rate discharge performance (1.0C) was significantly improved. This indicates that the composite nitrate system effectively improved solid-phase reaction kinetics and reduced electrochemical polarization through the synergistic effect among its multiple components, enabling the battery to maintain a high utilization rate of active materials even at high current densities. This performance improvement is of great significance for special power supplies that require high-current pulse operation (such as emergency positioning beacons and downhole oil well instruments).

[0030] The above description is merely a preferred embodiment of this application and does not limit the patent scope of this application. Any equivalent structural transformations made based on the inventive concept of this application and the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A room-temperature lithium metal primary battery with a positive electrode containing lithium nitrate active material, comprising a negative electrode, a positive electrode sheet, and a non-aqueous electrolyte, characterized in that, The positive electrode includes a current collector, a positive electrode coating coated on the current collector, and a composite nitrate dispersed in the positive electrode coating in the form of solid particles; the composite nitrate is composed of lithium nitrate and at least one other metal nitrate.

2. The primary battery according to claim 1, characterized in that, The other metal nitrates are selected from one or more of sodium nitrate, potassium nitrate, rubidium nitrate, cesium nitrate, magnesium nitrate, calcium nitrate, strontium nitrate, and barium nitrate.

3. The primary battery according to claim 2, characterized in that, In the composite nitrate, lithium nitrate accounts for 30% to 95% by mass, and other metal nitrates account for 5% to 70% by mass.

4. The primary battery according to claim 3, characterized in that, The positive electrode coating comprises, by mass ratio of components: 65-95% composite nitrate, 2-25% conductive agent, and 3-10% binder.

5. The primary battery according to claim 4, characterized in that, The conductive agent is selected from one or more of acetylene black, Super P, carbon nanotubes, graphene, and Ketjen black.

6. The primary battery according to claim 5, characterized in that, The adhesive is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylic acid, and LA133 waterborne adhesive.

7. The primary battery according to claim 1, characterized in that, The non-aqueous electrolyte contains lithium salts and non-aqueous organic solvents.

8. The primary battery according to claim 7, characterized in that, The lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, and lithium difluorooxalate borate; the non-aqueous organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, ethylene glycol dimethyl ether, 1,3-dioxolane, and tetraethylene glycol dimethyl ether.

9. The method for preparing a primary battery according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Preparation of composite positive electrode sheet: In a dry environment with a dew point below -40°C, lithium nitrate solid powder and at least one other metal nitrate solid powder are pre-mixed and ground in a certain proportion to obtain a composite nitrate precursor; the precursor is dispersed in a solvent with a conductive agent and a binder in a certain proportion and stirred and mixed evenly to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the surface of the current collector, and after drying, rolling and cutting, a composite positive electrode sheet is obtained; S2. Electrolyte preparation: Dissolve lithium salt in a non-aqueous organic solvent in an inert atmosphere or dry air environment, stir evenly, and a non-aqueous electrolyte is obtained. S3. Battery assembly: In an inert atmosphere or dry air environment, the prepared composite positive electrode, separator, and lithium metal negative electrode are stacked or wound in sequence, injected with the prepared non-aqueous electrolyte, sealed and left to stand to obtain a room temperature lithium metal primary battery.

10. The method for preparing a primary battery according to claim 9, characterized in that, The solvent mentioned in step S1 is N-methylpyrrolidone or deionized water.

Images