Negative-electrode-free lithium metal battery structure and application thereof

Abstract

The non-cathode lithium metal battery structure is characterized in that the non-cathode lithium metal battery structure comprises a copper current collector, an insulating isolation net, a diaphragm and a positive electrode, the positive electrode is located at the top of the non-cathode lithium metal battery structure, the insulating isolation net covers the surface of the copper current collector, and the diaphragm covers the surface of the copper current collector. The diaphragm is arranged between the positive electrode and the insulating isolation net, and the copper current collector, the insulating isolation net, the diaphragm and the positive electrode are all immersed in the electrolyte. The insulating separation net covers the surface of the copper current collector, so that electrolyte can be effectively separated, local space charges in the circulation process are reduced, and dendritic crystal growth is inhibited, so that the lithium deposition uniformity is improved, and dendritic crystal growth is inhibited; the insulating separation net is wide in material source, low in price and suitable for large-scale popularization. The negative-electrode-free lithium metal battery is reasonable in structural design, the energy density and the cycling stability of the negative-electrode-free lithium metal battery are effectively improved by additionally arranging the insulating separation net, meanwhile, the cost is low, and industrial application and popularization are facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium metal batteries and relates to a lithium metal battery structure, and in particular to a negative electrode-free lithium metal battery structure and application thereof. Background Art

[0002] The rapid development of electric vehicles and portable electronic products has put forward higher requirements for the energy density of secondary batteries. The theoretical specific capacity of lithium metal anode is as high as 3860mAh / g, which is 10 times that of graphite. It has an extremely low electrode potential (-3.04V vs. standard hydrogen electrode) and is considered to be the "holy grail" electrode in the next generation of high specific energy batteries. However, the uneven deposition / dissolution of lithium metal during the cycle leads to dendrite growth, which leads to a decrease in battery capacity and even causes safety accidents such as fire and explosion. Therefore, in order to make up for the loss of active lithium in each cycle, the lithium foil currently used contains excessive lithium, which reduces the energy density, processability and safety of lithium metal batteries. In order to solve the above problems, the negative electrode-free design avoids the use of excessive lithium in the negative electrode, and only uses copper current collectors or other non-lithium-based substrates as negative electrodes, which effectively improves the energy density of the battery and also shows significant advantages in terms of cost and production portability. However, due to the loss of lithium in each cycle, the capacity of negative electrode-free lithium metal batteries decays rapidly.

[0003] In order to improve the cycle stability of anode-free lithium metal batteries, a variety of control strategies have been developed, including current collector surface modification, electrolyte and separator design, and cut-off voltage / discharge depth control. However, due to the uneven deposition of lithium metal and the serious side reactions between lithium deposition and electrolyte, anode-free lithium metal batteries with both high coulombic efficiency and cycle stability remain a huge challenge. Summary of the invention

[0004] The first technical problem to be solved by the present invention is to provide a negative electrode-free lithium metal battery structure with reasonable structural design, good cycle stability and high energy density.

[0005] The second technical problem to be solved by the present invention is to provide an application of a negative electrode-free lithium metal battery structure.

[0006] The technical solution adopted by the present invention to solve the above-mentioned first technical problem is: a negative electrode-free lithium metal battery structure, characterized in that: the negative electrode-free lithium metal battery structure includes a copper current collector, an insulating isolation net, a diaphragm and a positive electrode, wherein the positive electrode is located at the top of the negative electrode-free lithium metal battery structure, the insulating isolation net covers the surface of the copper current collector, the diaphragm is arranged between the positive electrode and the insulating isolation net, and the copper current collector, the insulating isolation net, the diaphragm and the positive electrode are all immersed in the electrolyte.

[0007] Preferably, the material of the insulating isolation net includes but is not limited to one of polyethylene, glass fiber, polyester fiber, polyester fiber, nylon and cotton yarn.

[0008] Preferably, the structure of the insulating isolation net includes but is not limited to a mesh, a hole or a honeycomb.

[0009] Finally, the thickness of the insulating isolation net is between 0.01-1 mm, and the pore size is 1.25-800 μm.

[0010] The technical solution adopted by the present invention to solve the above-mentioned second technical problem is: an application of the above-mentioned negative electrode-free lithium metal battery structure, characterized in that: the negative electrode-free lithium metal battery structure is applied to the field of high specific energy lithium metal secondary batteries.

[0011] Compared with the prior art, the advantages of the present invention are:

[0012] Covering the surface of the copper current collector with an insulating isolation net can effectively separate the electrolyte, reduce the local space charge during the cycle, and inhibit the growth of dendrites, thereby improving the uniformity of lithium deposition and inhibiting the growth of dendrites; the material source of the insulating isolation net is wide, the price is low, and it is suitable for large-scale promotion. The structural design of the present invention is reasonable. By adding an insulating isolation net, the energy density and cycle stability of the negative electrode-free lithium metal battery are effectively improved. At the same time, the cost is low, which is conducive to industrial promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a structural schematic diagram of a negative electrode-free lithium metal battery structure provided by the present invention;

[0014] Figure 2 is an optical picture of the polyethylene net used in Example 1 of the present invention;

[0015] Figure 3 (a) to (b) are lithium deposition morphologies of Example 3 of the present invention;

[0016] Figure 4 (a) to 4(d) are the difference diagrams of lithium deposition morphology between Example 1 of the present invention and Comparative Examples 1 and 2;

[0017] Figure 5 The coulombic efficiency curves of Example 1 and Comparative Examples 1 and 2 of the present invention after being assembled into lithium metal batteries;

[0018] Figure 6 Cycle curves of Example 1 of the present invention and Comparative Examples 1 and 2 after being assembled into a symmetrical battery. DETAILED DESCRIPTION

[0019] The present invention is further described in detail below with reference to the accompanying drawings.

[0020] like Figures 1 to 6 As shown, a negative electrode-free lithium metal battery structure includes a copper current collector 1, an insulating isolation net 2, a diaphragm 3 and a positive electrode 4, wherein the positive electrode 4 is located at the top of the negative electrode-free lithium metal battery structure, the insulating isolation net 2 covers the surface of the copper current collector 1, the diaphragm 3 is arranged between the positive electrode 4 and the insulating isolation net 2, and the copper current collector 1, the insulating isolation net 2, the diaphragm 3 and the positive electrode 4 are all immersed in the electrolyte.

[0021] The material of the insulating isolation net 2 includes but is not limited to one of polyethylene, glass fiber, polyester fiber, polyester fiber, nylon and cotton yarn. The structure of the insulating isolation net 2 includes but is not limited to a mesh, a hole or a honeycomb. The thickness of the insulating isolation net 2 is between 0.01-1mm, and the pore size is 1.25-800μm.

[0022] The copper current collector 1, the separator 3 and the positive electrode 4 are consistent with the prior art and will not be described in detail here.

[0023] Example 1

[0024] A negative electrode-free lithium metal battery structure and its application, comprising the following steps:

[0025] (1) Use a polyethylene mesh with a thickness of 0.1 mm and a mesh size of 40 as an insulating isolation net (such as Figure 1 ), washing the polyethylene mesh with ethanol and deionized water, and drying it in a vacuum drying oven at 40-80° C.;

[0026] (2) punching the cleaned and dried polyethylene mesh into discs with a diameter of 12 mm;

[0027] (3) Assemble a negative electrode-free lithium metal battery in the order of lithium iron phosphate sheet, electrolyte, separator, electrolyte, polyethylene sheet, copper current collector, gasket, and spring.

[0028] Example 2

[0029] A negative electrode-free lithium metal battery structure and its application, comprising the following steps:

[0030] (1) A polyethylene mesh with a thickness of 0.1 mm and a mesh size of 80 is used as an insulating isolation mesh, the polyethylene mesh is cleaned with ethanol and deionized water, and dried in a vacuum drying oven at 40-80° C.;

[0031] (2) punching the cleaned and dried polyethylene mesh into discs with a diameter of 12 mm;

[0032] (3) Assemble a negative electrode-free lithium metal battery in the order of lithium iron phosphate sheet, electrolyte, separator, electrolyte, polyethylene sheet, copper current collector, gasket, and spring.

[0033] Example 3

[0034] A negative electrode-free lithium metal battery structure and its application, comprising the following steps:

[0035] (1) A polyethylene mesh with a thickness of 0.5 mm and a mesh size of 40 is used as an insulating isolation mesh, the polyethylene mesh is cleaned with ethanol and deionized water, and dried in a vacuum drying oven at 40-80° C.;

[0036] (2) punching the cleaned and dried polyethylene mesh into discs with a diameter of 12 mm;

[0037] (3) Assemble a negative electrode-free lithium metal battery in the order of lithium iron phosphate sheet, electrolyte, separator, electrolyte, polyethylene sheet, copper current collector, gasket, and spring.

[0038] Lithium deposition testing in anode-free lithium metal batteries:

[0039] At 0.3 mAh / cm 2 The capacity is 0.5mA / cm 2 Lithium was deposited on the surface of the copper current collector at a current density of 1.5 %. The deposition morphology of lithium was observed. Figure 3 (a) It can be seen that the lithium deposited on the surface of the copper current collector covered with the polyethylene mesh is dense and uniform. The lithium deposition at the polyethylene mesh line is also very dense and the outline of the mesh line can be observed, such as Figure 3 (b).

[0040] Comparative Example 1

[0041] In this comparative example, the copper current collector of the negative electrode-free lithium metal battery was prepared and the negative electrode-free lithium metal battery was assembled according to the following steps:

[0042] (1) Wipe the surface of a 9 μm copper foil clean with ethanol and dry it at 80°C for 3 h to obtain a negative electrode current collector;

[0043] (2) Assemble a negative electrode-free lithium metal battery in the order of lithium iron phosphate sheet, electrolyte, separator, electrolyte, copper current collector, gasket, and spring.

[0044] Comparative Example 2

[0045] In this comparative example, the copper current collector of the negative electrode-free lithium metal battery was prepared and the negative electrode-free lithium metal battery was assembled according to the following steps:

[0046] (1) Preparing microstructures on the surface of a copper current collector using a microindenter;

[0047] (2) wiping the surface of the copper current collector with the microstructure prepared with ethanol and drying at 80° C. for 3 h to obtain the negative electrode current collector;

[0048] (3) Assemble a negative electrode-free lithium metal battery in the order of lithium iron phosphate sheet, electrolyte, diaphragm, electrolyte, copper current collector, gasket, and spring.

[0049] Lithium deposition testing in anode-free lithium metal batteries:

[0050] At 0.3 mAh / cm 2 The capacity is 0.5mA / cm 2 Lithium was deposited on the surface of the copper current collector at a current density of 1.50 Å. The deposition morphology of lithium was observed. Figure 4 (a) to 4 (d) are the differences in the lithium deposition morphology between Example 1 and Comparative Examples 1 and 2. Figure 4 (a) to 4 (d) show that the lithium deposited on the surface of the copper current collector covered with the polyethylene mesh is dense and uniform ( Figure 4 a), the lithium deposition at the polyethylene mesh is also very dense and the mesh outline can be observed ( Figure 4 b). However, a large number of dendrites appeared on the surface of the copper current collector in Comparative Example 1, indicating the unevenness of lithium deposition ( Figure 4 c), the lithium deposition on the surface of the copper current collector with microstructure prepared in Comparative Example 2 is also relatively dense, and the lithium deposition morphology is mainly spherical ( Figure 4 d).

[0051] Electrochemical performance testing in anode-free lithium metal batteries:

[0052] At 1 mAh / cm 2 The capacity is 0.5mA / cm 2 Lithium was electrodeposited on the surface of copper current collector at a current density of 2.5 V and then charged to 1.5 V to compare the cycling stability of the battery. Figure 5 The Coulomb efficiency curves of Example 1 and Comparative Examples 1 and 2 after being assembled into lithium metal batteries. Figure 5 , the lithium metal battery using 40 mesh polyethylene mesh in Example 1 can stably cycle 80 times, and the average coulomb efficiency is 97.1%. The lithium metal battery using the copper current collector in Comparative Example 1 can only stably cycle 16 times, and the average coulomb efficiency is only 89.3%. The lithium metal battery using the copper current collector in Comparative Example 2 can stably cycle 50 times, and the average coulomb efficiency is 92.1%.

[0053] At 6 mAh / cm 2 The capacity is 1mA / cm 2 Lithium was electrodeposited on the surface of the copper current collector at a current density of 0.5 mA / cm 2 The current density is 0.5 mAh / cm 2 The charge and discharge depth of the battery is cycled to compare the cycle stability differences. Figure 6As shown, Example 1 can stably cycle for about 400 hours, and the cycle overpotential is stable at 30mV. The symmetrical battery in Comparative Example 1 can only stably cycle for 100 hours, and it fails after about 50 cycles, and the pre-deposited lithium has been completely lost. The symmetrical battery in Comparative Example 2 can stably cycle for 230 hours, and fails after about 115 cycles, and the cycle overpotential is not much different from that in Example 1.

[0054] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A negative electrode-free lithium metal battery structure, characterized in that: The negative electrode-free lithium metal battery structure includes a copper current collector, an insulating isolation net, a diaphragm and a positive electrode, wherein the positive electrode is located at the top of the negative electrode-free lithium metal battery structure, the insulating isolation net covers the surface of the copper current collector, the diaphragm is arranged between the positive electrode and the insulating isolation net, and the copper current collector, the insulating isolation net, the diaphragm and the positive electrode are all immersed in the electrolyte.

2. The negative electrode-free lithium metal battery structure according to claim 1, characterized in that: The material of the insulating isolation net includes but is not limited to one of polyethylene, glass fiber, polyester fiber, polyester fiber, nylon and cotton yarn.

3. The negative electrode-free lithium metal battery structure according to claim 2, characterized in that: The structure of the insulating isolation net includes but is not limited to a mesh, a hole or a honeycomb.

4. The negative electrode-free lithium metal battery structure according to claim 3, characterized in that: The thickness of the insulating isolation net is between 0.01-1 mm, and the pore size is between 1.25-800 μm.

5. An application of the negative electrode-free lithium metal battery structure according to claim 4, characterized in that: The negative electrode-free lithium metal battery structure is applied to the field of high specific energy lithium metal secondary batteries.

Images