A layered lithium metal composite anode for a thermal battery and a preparation method thereof

Abstract

The present invention provides a layered lithium metal composite anode for thermal batteries and a preparation method thereof. By simply mechanically rolling, two-dimensional materials such as graphene with good lithium wettability (lithophilic) are compounded with metallic lithium through mechanical rolling to prepare a layered lithium metal composite electrode. Due to the layered framework structure with a high specific surface area and a high metallic lithium content, when used as the anode of a thermal battery, the layered composite lithium electrode exhibits excellent high-current discharge performance and long-time discharge performance. At the same time, during the operation of the thermal battery, the molten metallic lithium is adsorbed and fixed inside the composite electrode structure by the lithophilic layered framework, reducing the safety risk caused by the overflow of metallic lithium in the thermal battery and increasing the safety of the thermal battery. The preparation method is simple, the layered structure is easy to adjust, and the adaptability is strong, which can meet the requirements of large-scale and diversified production of thermal batteries.

Description

Technical Field

[0001] The present invention belongs to the field of material chemistry, and particularly relates to a layered lithium metal composite anode for thermal batteries and a preparation method thereof. Background Art

[0002] A thermal battery is a thermally activated reserve battery, mainly composed of a heating layer, a positive electrode layer, an electrolyte layer, and a negative electrode layer. When the thermal battery receives an activation signal, the built-in heating system of the battery instantaneously heats up, melting the non-conductive solid electrolyte, enabling an electrochemical reaction between the positive and negative electrodes and realizing the output of electrical energy. Due to its unique advantages such as long storage life, short activation time, high current density, high output power, and strong environmental adaptability, it is widely used in the weapon field and emergency systems.

[0003] Due to the working characteristics of thermal batteries, the temperature inside the battery stack is usually greater than 400 °C after activation, which is higher than the melting point of lithium metal (180 °C). If metallic lithium is directly used as the negative electrode of a thermal battery, it is easy to cause lithium to melt and liquefy, and then flow out of the battery stack, resulting in a short circuit of the battery stack and triggering a safety accident. Therefore, the commonly used negative electrode materials for thermal batteries are lithium-silicon alloys and lithium-boron alloys that are solid at high temperatures. Among them, the theoretical capacity of lithium-silicon alloys is low (1747 A·s·g -1 ), and the commonly used lithium-boron alloys have a higher capacity (3000 A·s·g according to the content of metallic lithium in them -1 -8000 A·s·g -1 ), but their skeleton occupies a relatively large proportion and the wettability of the skeleton structure to metallic lithium is poor. Especially when the content of metallic lithium is high (corresponding capacity ≥ 4000 A·s·g -1 ), it is easy to cause the overflow of metallic lithium, leading to serious safety problems, and cannot meet the requirements of high specific power, high specific capacity, and high safety for thermal batteries with the development of technology in the weapon field. Summary of the Invention

[0004] The present invention provides a layered lithium metal composite anode for thermal batteries and a preparation method thereof. It is characterized in that a lithiophilic two-dimensional material such as graphene is compounded with metallic lithium by simple mechanical rolling to prepare a layered composite lithium electrode.

[0005] The technical solution for achieving the object of the present invention is: a layered lithium metal composite anode for thermal batteries, which is formed by alternately stacking and rolling a two-dimensional matrix material and lithium metal; the two-dimensional matrix material and lithium metal are alternately distributed in a layered manner in the composite anode, and the thickness of each layer is adjustable according to the process, and the single-layer thickness range is 1 nm - 0.5 mm.

[0006] A preparation method of the layered lithium metal composite anode for thermal batteries as described above includes:

[0007] Stack the lithiumophilic two-dimensional matrix material and lithium metal alternately and perform rolling;

[0008] Continue to stack the lithiumophilic two-dimensional matrix material and the above rolling product alternately and perform rolling, repeat 0 to 20 times, to prepare a layered lithium metal composite negative electrode material.

[0009] Preferably, the lithiumophilic two-dimensional matrix material is a two-dimensional material film layer or a two-dimensional material film layer attached to the surface of a metal foil or two-dimensional material powder.

[0010] Preferably, the lithiumophilic two-dimensional matrix material is one or a mixture of graphene infiltrated with lithium, titanium carbide, boron nitride, black phosphorus, etc.

[0011] Preferably, when the lithiumophilic two-dimensional matrix material is graphene oxide powder,

[0012] S1: Uniformly spread 0.5 g - 5 g of graphene oxide powder on the surface of a lithium strip with a thickness of 0.5 mm - 2 mm;

[0013] S2: Stack 3 to 5 lithium strips prepared in S1 in sequence and perform mechanical rolling; the roll gap parameter of the rolling machine is set to 1.5 mm - 10 mm, and repeat rolling 1 to 20 times;

[0014] S3: After folding the above rolled lithium strip, uniformly spread 0.2 g - 4 g of graphene oxide powder on its surface and then perform mechanical rolling. The roll gap parameter of the rolling machine is set to 1.5 mm - 10 mm, and repeat rolling 1 to 20 times;

[0015] S4: Repeat S3 0 to 20 times to prepare a layered lithium metal composite negative electrode.

[0016] Preferably, when the lithiumophilic two-dimensional matrix material is a graphene oxide film layer,

[0017] S1: Add 200 ml - 2000 ml of an aqueous solution of graphene oxide (GO) with a mass fraction of 20% - 80% to the filter cup for vacuum filtration, perform suction filtration, and vacuum dry the suction filtration product to prepare a GO film;

[0018] S2: Place the GO film prepared in S1 into a high-temperature furnace, after inert gas protection, introduce hydrogen, heat up to 200°C - 600°C, keep warm for 10 min - 60 min, and obtain a partially reduced graphene oxide film (rGO film) after the heat preservation ends, and cut it into a sheet structure;

[0019] S3: Alternately stack the rGO films prepared in two steps of S2 with lithium metal strips having a thickness of 0.2 mm - 2 mm, and then perform rolling; set the roll gap parameter of the rolling machine to 1.5 mm - 10 mm, and repeat the rolling 1 - 20 times; cut the rolled composite structure to obtain a composite sheet structure;

[0020] S4: Alternately stack the composite sheet structure prepared in the previous step with the rGO film prepared in S2, and then perform rolling; set the roll gap parameter of the rolling machine to 1.5 mm - 10 mm, and repeat the rolling 1 - 20 times;

[0021] S5: Repeat S4 for 0 - 20 times to prepare a layered lithium metal composite negative electrode.

[0022] Preferably, vacuum dry the suction filtration product at 25°C - 80°C for 4 h - 24 h to prepare a GO film.

[0023] Preferably, when the two-dimensional matrix material is a reduced graphene oxide film layer,

[0024] S1: Uniformly spray 50 ml - 2000 ml of a reduced graphene oxide (rGO) ethanol solution with a mass fraction of 10% - 70% onto the surface of a copper foil with a thickness of 0.1 mm - 0.5 mm, and vacuum dry at 25°C - 80°C for 6 h - 12 h to prepare a composite copper foil with an rGO film, and cut it into a sheet structure;

[0025] S2: Clamp a lithium strip with a thickness of 0.5 mm - 2 mm with two composite copper foils prepared in S1, with the side of the composite copper foil with rGO in contact with the lithium metal, and perform rolling along the long side of the copper foil. Set the roll gap parameter of the rolling machine to 0.2 mm - 1.9 mm. After rolling, remove the copper foils on both sides to obtain a composite lithium strip;

[0026] S3: Fold the composite lithium strip prepared in the previous step several times, and then perform rolling. Set the roll gap parameter of the rolling machine to 0.5 mm - 2 mm, repeat the rolling 1 - 20 times, then cut the lithium strip, stack it with two composite copper foils with rGO films prepared in S1, with the side of the composite copper foil with rGO in contact with the composite lithium strip, roll 1 - 5 times, and remove the copper foils on both sides to obtain a composite lithium strip;

[0027] S4: Repeat S3 for 0 - 20 times to prepare a layered lithium metal composite negative electrode.

[0028] Preferably, the change rate of the roll gap parameter of the rolling machine each time does not exceed 50% - 90% of the previous time, and the number of repetitions under the same roll gap parameter is 1 - 20 times.

[0029] A thermal battery includes the negative electrode described above, and the negative electrode is prepared by the method described above.

[0030] The layered lithium metal composite anode for thermal batteries of the present invention has the following advantages: The present invention prepares a layered lithium metal composite electrode by simply mechanically rolling and compounding conductive two-dimensional materials such as graphene and titanium carbide with metallic lithium. Due to the layered framework structure with a high specific surface area and a high metallic lithium content, when used as the anode of a thermal battery, this layered lithium anode exhibits excellent high-current discharge performance and long-term discharge performance. At the same time, during the operation of the thermal battery, the molten metallic lithium is adsorbed and fixed inside the electrode structure by the layered framework with a high specific surface area, reducing the safety risk caused by the overflow of metallic lithium in the thermal battery and increasing the safety of the thermal battery. This preparation method is simple, the layered structure is easy to adjust, and it has strong adaptability, capable of meeting the requirements of large-scale and diversified production of thermal batteries.

[0031] (1) The present invention utilizes the ductility of metallic lithium and two-dimensional materials themselves to prepare a layered lithium metal composite electrode, and for the first time uses it as the anode of a thermal battery, enabling it to simultaneously exhibit the characteristics of high specific capacity and high-temperature safety;

[0032] (2) The layered lithium metal composite anode prepared by the present invention uses metallic lithium as the active substance to provide the electrons and ions required for the discharge of the thermal battery. With a two-dimensional material with a high specific surface area as the framework structure, the molten metallic lithium during the working state is fixed inside the framework structure, and simultaneously exhibits the characteristics of high capacity, high rate, and safety and stability, having good application prospects;

[0033] (3) The method for preparing the layered lithium metal composite anode adopted by the present invention is a simple mechanical rolling method. The method is simple, easy to operate, has strong adaptability, and is conducive to large-scale promotion and use. Detailed implementation mode

[0034] The technical solutions of the present invention are described below through specific embodiments. It should be understood that one or more steps mentioned in the present invention do not exclude the existence of other methods and steps before and after the combined steps, or other methods and steps can be inserted between these clearly mentioned steps. It should also be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. Unless otherwise specified, the numbers of each method step are only for the purpose of identifying each method step, rather than limiting the arrangement order of each method or defining the implementation scope of the present invention. The change or adjustment of their relative relationship, under the condition of no substantial change in technical content, can also be regarded as the scope in which the present invention can be implemented.

[0035] There are no specific restrictions on the sources of the raw materials and instruments used in the embodiments, and they can be purchased on the market or prepared according to the conventional methods well-known to those skilled in the art.

[0036] It should be understood that one or more steps mentioned in the present invention do not exclude the existence of other methods and steps before and after the combined steps, or other methods and steps can be inserted between these explicitly mentioned steps.

[0037] Example 1:

[0038] Step 1: Uniformly spread 0.5 g - 5 g of graphene oxide (GO) powder on the surface of a lithium strip with a width of 50 mm and a length of 100 mm and a thickness of 0.5 mm - 2 mm.

[0039] Step 2: Stack 3 - 5 lithium strips prepared as above in sequence, and perform mechanical rolling. The roll gap parameter of the rolling machine is set to 1.5 mm - 10 mm, and the rolling is repeated 1 - 20 times.

[0040] Step 3: After folding the rolled lithium strip, uniformly spread 0.2 g - 4 g of graphene oxide powder on its surface, and then perform mechanical rolling. The roll gap parameter of the rolling machine is set to 1.5 mm - 10 mm, and the rolling is repeated 1 - 20 times.

[0041] Step 4: After repeating Step 3 (0 - 20 times), a layered lithium metal composite negative electrode can be prepared.

[0042] The lithium layer thickness of the composite lithium metal negative electrode prepared by this method is about 10 nm - 800 nm. When this composite electrode is used as the negative electrode of a thermal battery for discharge testing, its discharge capacity is 4600 A·s·g -1 , and no metal lithium spillage occurs after working at high temperature for 30 min.

[0043] Example 2:

[0044] Step 1: Add 200 ml - 2000 ml of graphene oxide aqueous solution with a mass fraction of 20% - 80% to the filter cup for vacuum filtration. The filtered product is vacuum dried at 25°C - 80°C for 4 h - 24 h to prepare a GO film.

[0045] Step 2: Place the prepared GO film in a high - temperature furnace. After argon protection, hydrogen is introduced, and the temperature is raised to 200°C - 600°C and kept warm for 10 min - 60 min. After the heat preservation ends, a partially reduced graphene oxide film (rGO film) is obtained. The rGO film layer is cut into a sheet structure of 50 mm × 70 mm.

[0046] Step 3: Alternately place two rGO films prepared in Step 2 and a lithium strip with a thickness of 0.2 mm - 2 mm and a size of 50 mm × 50 mm, and then perform rolling. The roll gap parameter of the rolling machine is set to 1.5 mm - 10 mm, and the rolling is repeated 1 - 20 times. The prepared composite structure is cut into a sheet of 50 mm × 50 mm

[0047] Step 4: Alternately stack the composite sheet structure prepared in the previous step and the rGO film with a size of 50 mm × 70 mm prepared in Step 2, and then perform rolling. The roll gap parameter of the rolling machine is set to 1.5 mm - 10 mm, and the rolling is repeated 1 - 20 times;

[0048] Step 5: Repeat Step 4 (0 - 20 times) to prepare a layered lithium metal composite negative electrode.

[0049] The lithium layer thickness of the composite lithium metal negative electrode prepared by this method is about 10 - 2000 nm. When this composite electrode is used as the negative electrode of a thermal battery for discharge testing, its discharge capacity is 5200 A·s·g -1 , and no lithium metal overflows after working at high temperature for 30 min.

[0050] Example 3:

[0051] Step 1: Uniformly spray 50 ml - 2000 ml of a reduced graphene oxide (rGO) ethanol solution with a mass fraction of 10% - 70% onto the surface of a copper foil with a thickness of 0.1 mm - 0.5 mm, and vacuum dry it at 25°C - 80°C for 6 h - 12 h to prepare a composite copper foil with an rGO film. Cut the composite copper foil into 50 mm × 100 mm;

[0052] Step 2: Sandwich a lithium strip with a size of 50 mm (length) × 50 mm (width) and a thickness of 0.5 mm - 2 mm between two pieces of the composite copper foil prepared in Step 1. The side of the composite copper foil with rGO is in close contact with the lithium metal, and roll along the long side of the copper foil. The roll gap parameter of the rolling machine is set to 0.2 mm - 1.9 mm. After rolling, remove the copper foils on both sides to obtain a composite lithium strip;

[0053] Step 3: Fold the composite lithium strip prepared in the previous step several times and then perform rolling. The roll gap parameter of the rolling machine is set to 0.5 mm - 2 mm. After repeating the rolling 1 - 10 times, cut the lithium strip into 50 mm (length) × 50 mm (width), stack it with two pieces of the composite copper foil with rGO film prepared in Step 1. The side of the composite copper foil with rGO is in close contact with the composite lithium strip, and roll along the long side of the copper foil 1 - 5 times. After removing the copper foils on both sides, obtain a composite lithium strip;

[0054] Step 4: Repeat Step 3 (0 - 20 times) to prepare a layered lithium metal composite negative electrode.

[0055] The lithium layer thickness of the composite lithium electrode prepared by this method is about 100 nm - 3000 nm. When this composite electrode is used as the negative electrode of a thermal battery for discharge testing, the capacity is 5600 A·s·g -1, there was no case of lithium metal overflow after working at high temperature for 30 minutes.

[0056] The above embodiments merely describe the specific implementation manners of the present invention, rather than limiting the scope of the present invention. Those skilled in the art can make various modifications and changes based on the prior art. Without departing from the design spirit of the present invention, various variations and improvements made by ordinary engineering technicians in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

[0057] The parts not detailed in the present invention belong to the common general knowledge of those skilled in the art.

Claims

1. A preparation method of a layered lithium metal composite negative electrode for a thermal battery, characterized in that The preparation method includes: S1: Uniformly spray 50 ml - 2000 ml of a reduced graphene oxide (rGO) ethanol solution with a mass fraction of 10% - 70% onto the surface of a copper foil with a thickness of 0.1 mm - 0.5 mm, and vacuum dry it at 25°C - 80°C for 6 h - 12 h to obtain a composite copper foil with an rGO film, which is cut into a sheet structure; S2: Clamp a lithium strip with a thickness of 0.5 mm - 2 mm with two composite copper foils prepared in S1, with the side of the composite copper foil with rGO in close contact with the lithium metal, and roll along the long side of the copper foil. Set the roll gap parameter of the rolling press to 0.2 mm - 1.9 mm. After rolling, remove the copper foils on both sides to obtain a composite lithium strip; S3: After folding the composite lithium strip prepared in the previous step several times, roll it. Set the roll gap parameter of the rolling press to 0.5 mm - 2 mm. After repeating the rolling 1 - 20 times, cut the lithium strip and stack it with two composite copper foils with rGO films prepared in S1, with the side of the composite copper foil with rGO in close contact with the composite lithium strip, and roll 1 - 5 times. After removing the copper foils on both sides, obtain a composite lithium strip; S4: Repeat S3 0 - 20 times to prepare a layered lithium metal composite negative electrode.

2. The preparation method according to claim 1, characterized in that: The change rate of the roll gap parameter of the rolling press each time does not exceed 50% - 90% of the previous time, and the number of repetitions under the same roll gap parameter is 1 - 20 times.

3. A thermal battery, characterized in that It includes a layered lithium metal composite negative electrode for a thermal battery, and the negative electrode is prepared by the method according to one of claims 1 - 2.