CN216773280U - Metallic lithium negative electrode and secondary battery - Google Patents

Abstract

A metallic lithium anode and a secondary battery are provided. The metallic lithium negative electrode comprises a lithium current collector with a sandwich structure, a metallic lithium strip or a lithium alloy strip attached to the surface of the current collector and a lug, wherein the sandwich structure of the lithium current collector is formed by an intermediate polymer film and lithium layers positioned on two sides of the polymer film. The lithium current collector can replace copper foil to be directly used as the current collector, so that the specific capacity of the battery is greatly improved, and the coiled metal lithium negative electrode can be produced in batch because the metal lithium negative electrode is flexible.

Description

Metallic lithium negative electrode and secondary battery

Technical Field

The utility model relates to the technical field of energy storage, in particular to a novel light flexible metal lithium cathode for a secondary battery.

Background

Lithium batteries are widely used in the fields of aerospace, computers, mobile communication devices, electric vehicles, and the like due to their advantages of high energy density, long cycle life, and wide applicable temperature range. With the development of society and the progress of science and technology, the requirements on the energy density and the cycle life of a lithium battery are higher and higher, but the lithium ion battery which only uses graphite as a negative electrode at present cannot meet the social requirements, so that a novel positive and negative electrode material with higher specific capacity needs to be developed. For the negative electrode material, the lithium metal has high specific capacity (3860mAh/g, which is 10 times of that of a graphite negative electrode) and the lowest oxidation-reduction potential (-3.04V VS standard hydrogen potential), so that the specific energy of the battery can be effectively improved.

In the existing formed battery, lithium iron phosphate, lithium cobaltate or high nickel ternary material is used as the anode material, the anode material contains lithium, and the cathode uses little metal lithium (the thickness of the metal lithium is less than 50 um); because the metal lithium is soft, if the thickness of the metal lithium is less than 50um, the metal lithium is easy to break and adhere without a support film, so the currently used metal lithium negative electrode generally adopts a lithium-copper composite belt, and copper also plays a role in supporting while being used as a current collector. The thickness of the copper foil used in the current secondary battery is 6-8um, the copper foil accounts for about 13% of the total mass of the battery, and the specific energy of the battery needs to be further improved.

SUMMERY OF THE UTILITY MODEL

In order to improve the specific energy of the battery, the inventor of the present invention has found that a light flexible metallic lithium negative electrode can be obtained without using a copper foil by using a lithium current collector having a sandwich structure and a metallic lithium ribbon or a lithium alloy ribbon and a tab attached to the surface of the lithium current collector.

Specifically, the inventors found the following problems when trying to replace copper foil with a polymer support film and directly compound a metal lithium tape thereon, on one hand, the polymer film material has a small binding force with metal lithium, and a large pressure is applied to obtain a stable metal lithium negative electrode, which easily causes wrinkling and even breakage of the metal lithium tape; on the other hand, both the polymer film material and the lithium metal tape are flexible, and the rigidity of the formed lithium metal negative electrode is insufficient. Therefore, the inventor has further studied and found that when a polymer film is used as a support material, if an ultrathin lithium layer is deposited on the polymer support film and then a metal lithium strip is compounded, the compounding pressure can be significantly reduced, and the rigidity of the formed metal lithium negative electrode is better. Thus, the present invention has been completed.

Accordingly, one aspect of the present invention is directed to a metallic lithium negative electrode including a lithium current collector having a sandwich structure formed of an intermediate polymer film and lithium layers on both sides of the polymer film, a metallic lithium ribbon or a lithium alloy ribbon attached on a surface of the lithium current collector, and tabs placed on a surface of the lithium current collector in contact with the metallic lithium ribbon or the lithium alloy ribbon.

Optionally, the polymer film has a thickness of 3-10 um.

Alternatively, the thin lithium layers each have a thickness of 20nm-3um, preferably 100nm-2um, more preferably 0.5-2 um.

Alternatively, the thickness of the metallic lithium or lithium alloy ribbon is 5-100um, preferably 5-50um, more preferably 5-20 um.

Optionally, the polymer film layer comprises at least one of polyethylene, polypropylene, polyethylene terephthalate, polycarbonate, polydiformylphenylenediamine, polyvinyl chloride, polystyrene, polytetrafluoroethylene, polyvinylidene fluoride, polyamide, polyimide, polystyrene, polybutylene terephthalate, polyparaphenylene terephthalamide, acrylonitrile-butadiene-styrene copolymer, aramid, epoxy resin, polyoxymethylene, phenolic resin, silicone rubber, starch and derivatives thereof, cellulose and derivatives thereof, protein and derivatives thereof, polyethylene glycol and cross-linked products thereof, polyvinyl alcohol and cross-linked products thereof.

Alternatively, the lithium alloy is an alloy of metallic lithium with one or more of Ag, Al, Au, Ba, Be, Bi, C, Ca, Cd, Co, Cr, Cs, Fe, Ga, Ge, Hf, Hg, In, Ir, K, Mg, Mn, Mo, N, Na, Nb, Ni, Pt, Pu, Rb, Rh, S, Se, Si, Sn, Sr, Ta, Te, Ti, Y, V, Zn, Zr, Pb, Pd, Sb and Cu. By adjusting the amount of the alloying element, the amount of metallic lithium (effective lithium) can be controlled without changing the thickness of the lithium-containing layer. The content of metallic lithium in the lithium alloy is generally 10 to 90% by weight.

Optionally, the thickness of the tab is less than or equal to that of the lithium metal strip or the lithium alloy strip.

Optionally, one side edge of the lithium current collector in the width direction thereof is aligned with the lithium metal strip or lithium alloy strip, and the other side edge is covered by the tab.

Optionally, the lithium metal negative electrode is a rolled negative electrode, wherein a lateral width of the lithium metal strip or lithium alloy strip is smaller than a lateral width of the lithium current collector, and a sum of the lateral widths of the lithium metal strip or lithium alloy strip and the tab is larger than the lateral width of the lithium current collector.

Another aspect of the present invention provides a secondary battery comprising the above-described metallic lithium negative electrode.

Optionally, the secondary battery further comprises a positive electrode/separator/electrolyte or a positive electrode/solid electrolyte.

Alternatively, the metal lithium cathode can be directly used as a cathode of a secondary battery and can be assembled with a positive electrode/electrolyte/diaphragm to form a liquid secondary battery; or can be assembled with a positive electrode/solid electrolyte (with or without electrolyte) to form a semi-solid or solid secondary battery.

Alternatively, the positive electrode active material may be selected from lithium iron phosphate, lithium cobaltate, high nickel ternary material (NCM nickel cobalt manganese ternary or NCA nickel cobalt aluminum ternary), and the like.

Alternatively, the separator may be selected from a polypropylene (PP) film or a polypropylene/polyethylene/polypropylene (PP/PE/PP) three-layer composite film, and the separator may have a ceramic or layer thereon.

Alternatively, the solid electrolyte may be selected from the group consisting of a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte (e.g., PEO, PVDF, PAN, etc., and lithium salt composition), a sulfide solid electrolyte and a polymer mixed electrolyte, an oxide solid electrolyte, and a polymer mixed electrolyte.

Optionally, the electrolyte is selected from an ester electrolyte or an ether electrolyte.

Alternatively, the secondary battery has a laminated or wound structure.

The utility model achieves at least one of the following advantages:

1. the specific energy of the lithium metal negative electrode can be improved by about 10 percent compared with the battery using the copper foil as the current collector (the density of the copper foil is 8.93 g/cm)³The metallic lithium density was 0.534g/cm³The density of the polymer film material is 0.7-1.4 g/cm³Since metal lithium and polymer film materials are both light materials, the energy density of the battery is improved by about 10% compared with that of a battery using a copper foil current collector).

2. The metal lithium negative electrode can be directly used as a current collector because the metal lithium has conductivity.

3. The lithium metal cathode is a coiled material and can be produced in batch by a roll-to-roll process.

Drawings

Fig. 1 is a schematic structural view of a lithium metal anode of the present invention;

fig. 2 is a schematic sectional view taken along the plane a-a of fig. 1.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the utility model and are not intended to limit the utility model. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

Fig. 1 is a schematic structural view of a lithium metal anode of the present invention. The lithium metal anode includes: a polymer film material 1; lithium layers 2 on both upper and lower surfaces of the polymer film 1; a lithium strip/lithium alloy strip 3 and a tab 4 laminated in a juxtaposed manner on the lithium layer 2 (the lithium strip/lithium alloy strip 3 and the tab 4 are juxtaposed in contact in the a-a direction shown in fig. 1). The polymer film material 1 and the lithium layers 2 on the two sides jointly form a lithium current collector. One side of the lithium current collector is aligned with the lithium metal strip or the lithium alloy strip, and the edge of the other side is covered by the tab.

Fig. 2 is a schematic sectional view taken along the plane a-a of fig. 1. The positional relationship of the polymer film 1, the lithium layer 2, the lithium strip/lithium alloy strip 3 and the tab 4 is clearly shown.

The lithium metal negative electrode can be produced by the following method: respectively carrying out vapor deposition on a thin lithium layer 2 on the upper surface and the lower surface of a polymer film material 1 (the polymer film material 1 and the lithium layers 2 on the two sides form a lithium current collector), and rolling and laminating a lithium belt/lithium alloy belt 3 on the upper surface and the lower surface of the lithium current collector to obtain a metal lithium cathode; before or at the same time of compounding the lithium strip/lithium alloy strip 3, respectively rolling a compound copper strip (the width of the copper strip can be 15-30mm) on the upper surface and the lower surface of an edge area (the width of the edge area can be 5-10mm) on one side of a lithium current collector to form the tab 4.

Fig. 1 shows only the pattern of the lithium metal negative electrode and the lead tab formed on the upper surface of the polymer film, and the pattern of the lithium metal negative electrode and the lead tab formed on the lower surface of the polymer film is consistent with the pattern of the upper surface of the polymer film.

The rolling of the tab and the rolling of the composite lithium/lithium alloy strip on the thin lithium current collector may be performed simultaneously or in two passes.

When the thickness of the copper strip is consistent with that of the lithium/lithium alloy strip, for example, the thickness of the copper strip or the lithium/lithium alloy strip is 5-10um, the process of pressure compounding the lug and the lithium/lithium alloy strip on the lithium current collector can be carried out simultaneously. For example, a thin lithium current collector, two upper and lower coils of lithium/lithium alloy metal strips, and two upper and lower coils of copper strips can be simultaneously unwound under the same pressure, and the two coils are combined under the pressure of a rolling press to obtain a lithium metal negative electrode with a tab.

When the thickness of the copper strip is smaller than that of the lithium/lithium alloy strip, for example, the thickness of the copper strip is 5-10um, and the thickness of the lithium/lithium alloy strip is larger than 10um, under the condition, the copper strip needs to be firstly compounded on the upper and lower lithium layers of the lithium current collector 5, so as to obtain the current collector with the copper strip tabs on the two sides; and then, the current collector with copper strip tabs on both sides and the upper and lower metal lithium/lithium alloy tapes are unreeled and compounded by rolling again to obtain the metal lithium cathode with the tab.

Example 1:

preparation of a lithium metal negative electrode a: using coiled PET film as support film with thickness of 4um, drying coiled PET film in vacuum oven at 60 deg.C for 24 hr, and vacuum evaporating in vacuum evaporation equipment (vacuum degree of 10)^-3And (3) evaporating and plating thin lithium layers on the upper surface and the lower surface of the coiled PET film within Pa and the temperature of 500 ℃, wherein the thickness of the thin lithium layers is 1um, and thus obtaining the thin lithium current collector. And (3) compounding an upper coil of lithium belt and a lower coil of lithium belt (with the thickness of 20um) on a thin lithium current collector in a drying workshop (with the dew point of-45 ℃) by means of a winding and unwinding device and a rolling machine under the pressure of 3Mpa to obtain a coiled lithium metal cathode A.

Battery assembly and test 1: the metal lithium negative electrode A is used as a negative electrode, and the positive electrode adopts a lithium iron phosphate material (the single-side surface density is 15.5 mg/cm)²) The negative electrode is cut into 45 mm and 58mm by a punching device, the positive electrode is cut into 43 mm and 56mm, a PP film of Celgard2500 type is adopted as a diaphragm, a laminating machine is adopted to assemble the soft package battery, 1M LiPF6 is adopted as electrolyte, and EC: EMC is 3: 7 (vol/vol). The test voltage range is 2-3.7V, and the charge-discharge current is 0.5C.

Comparative example 1:

preparation of lithium metal negative electrode B: using the coiled copper foil as a current collector, wherein the thickness of the copper foil is 6um, and drying the coiled copper foil in a vacuum oven for 24 hours at 80 ℃; and (3) compounding an upper roll of lithium strip and a lower roll of lithium strip (with the thickness of 20um) on a copper foil current collector in a drying workshop (with the dew point of-45 ℃) by means of reeling and unreeling equipment and a rolling machine under the pressure of 5Mpa to obtain a coiled metal lithium cathode B.

Battery assembly and test 2: the procedure for assembling and testing the negative electrode using the metallic lithium negative electrode B, the positive electrode, the separator, the electrolyte, and the battery was the same as that of the battery assembly and test 1 in example 1.

Table 1 shows the specific energy comparison between example 1 and comparative example 1:

specific energy measurement method: assembling the soft package battery, and weighing the weight of the soft package battery; the discharge capacity and platform voltage of the soft package battery are tested by a certain current charge-discharge cycle on a battery tester, and the specific energy of the battery is calculated according to the following formula:

specific energy (discharge capacity platform voltage)/weight of the cell.

As can be seen from comparison between example 1 and comparative example 1, the specific energy of the battery using the polymer film and the thin lithium layer as the current collectors and the battery using the pure copper foil as the current collectors are respectively improved by 8.59-8.78%, and the requirement of the current high specific energy battery is met.

Claims (9)

1. A lithium metal anode characterized by: the lithium metal negative electrode comprises a lithium current collector with a sandwich structure, a lithium metal strip or a lithium alloy strip attached to the surface of the lithium current collector and tabs, wherein the sandwich structure of the lithium current collector is formed by a middle polymer film and lithium layers positioned on two sides of the polymer film, and the tabs are contacted with the lithium metal strip or the lithium alloy strip and are arranged on the surface of the lithium current collector.

2. The lithium metal anode of claim 1, wherein the polymer film has a thickness of 3-10 um.

3. The lithium metal anode of claim 1, wherein the lithium layers are each 20nm-3um thick.

4. The lithium metal anode of claim 1, wherein the lithium metal ribbon or lithium alloy ribbon has a thickness of 5-100 um.

5. The lithium metal anode of claim 1, wherein one side edge of the lithium current collector in a width direction thereof is aligned with the lithium metal strip or the lithium alloy strip, and the other side edge is covered with the tab.

6. The lithium metal anode of claim 1, wherein the lithium metal anode is a rolled anode, wherein the lateral width of the lithium metal strip or lithium alloy strip is less than the lateral width of the lithium current collector, and the sum of the lateral widths of the lithium metal strip or lithium alloy strip and the tab is greater than the lateral width of the lithium current collector.

7. The lithium metal anode of claim 1, wherein the tab has a thickness equal to or less than a thickness of a lithium metal strip or a lithium alloy strip.

8. A secondary battery comprising the lithium metal anode of any one of claims 1 to 7.

9. The secondary battery according to claim 8, wherein the secondary battery has a laminated or wound structure.

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