Electrochemical device and electronic device including the same

Abstract

The present application discloses an electrochemical device, belonging to the field of battery technology. An electrochemical device includes a negative electrode sheet and a negative electrode tab, wherein the negative electrode sheet includes a sheet region and a tab region, wherein the tab region is adjacent to the sheet region; both the sheet region and the tab region include a lithium-containing metal belt, wherein the non-lithium element content in the lithium-containing metal belt is m1, and the value range of m1 is 0wt%≤m1≤10wt%; wherein a reinforcement device is provided in the tab region; the reinforcement device includes a metal foil, and the negative electrode tab is connected to the metal foil. This design can not only ensure that the electrochemical device has a high energy density, but also improve the stability of the tab during the charging and discharging process, and enhance the cycle performance of the electrochemical device.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a lithium metal battery and its preparation. Background Art

[0002] Electrochemical devices such as lithium-ion batteries have advantages such as high specific energy, high operating voltage, low self-discharge rate, small size, and light weight, and are widely used in the field of consumer electronics. However, with the rapid development of electric vehicles and mobile electronic devices, people have increasingly higher demands on the energy density, safety, and cycle performance of electrochemical devices.

[0003] Lithium metal is the metal with the smallest relative atomic mass and the lowest standard electrode potential among all metal elements, and its theoretical gram capacity can reach 3860mAh / g. Therefore, using lithium metal as the negative electrode of the battery, combined with some high-energy-density positive electrode materials, can greatly improve the energy density and operating voltage of the electrochemical device. At present, electrochemical devices such as lithium metal batteries usually use lithium-coated copper strips as negative electrode plates and copper foil as negative electrode current collectors, which makes it difficult to give full play to their energy density advantages. Summary of the invention

[0004] This patent introduces an electrochemical device, which improves the energy density of the electrochemical device while achieving stability in the lug area (especially the lug connection area) during the cycle, thereby improving the cycle performance of the electrochemical device by locally setting a reinforcement device in the lug area, or by alloying the negative electrode plate as a whole, or by differentially alloying the negative electrode plate locally.

[0005] An electrochemical device comprises a negative electrode plate and a negative electrode tab, wherein the negative electrode plate comprises a plate region and a tab region, wherein the tab region is adjacent to the plate region; both the plate region and the tab region comprise a lithium-containing metal strip, wherein the lithium-containing metal strip contains non-lithium elements m1, and the value range of m1 is 0wt%≤m1≤10wt%; wherein a reinforcement device is arranged in the tab region; the reinforcement device comprises a metal foil, and the negative electrode tab is connected to the metal foil.

[0006] Optionally, the lithium-containing metal strip comprises a lithium strip or a lithium-containing alloy strip;

[0007] The material used for the lithium-containing alloy strip includes any one of the alloys shown in Formula I;

[0008] Li-A 1 Formula I

[0009] Among them, A 1 The element is selected from at least one of Ag, Al, B, Mg, Au, Na, Si, Sn, Zn, Ba, Bi, C, Ca, Ge, Cs, Ga, K, Pb, P or Sb.

[0010] Optionally, the lithium-containing alloy strip includes any one of Li-Ag, Li-Al, Li-B, Li-Mg, Li-Au, Li-Na, Li-Si, Li-Sn, Li-Zn, Li-Ba, Li-Bi, Li-C, Li-Ca, Li-Ge, Li-Cs, Li-Ga, Li-K, Li-Pb, Li-P, Li-Sb, Li-B-Mg or Li-Mg-Si.

[0011] Optionally, the metal foil includes any one of Cu foil, Mg foil, Al foil or Ti foil.

[0012] Optionally, the metal foil is wrapped around a local position of the tab region; or,

[0013] The metal foil is attached to a local position of the tab region.

[0014] Optionally, the connection width between the negative electrode tab and the reinforcement device is L1, and the width of the reinforcement device is L2;

[0015] The relationship between L1 and L2 satisfies the formula shown in formula ⅰ:

[0016] L1<L2 Formula Ⅰ

[0017] The value range of L2 is 1mm≤L2≤10mm.

[0018] Optionally, the thickness of the metal foil is d1, and the value range of d1 is 8 μm≤d1≤50 μm.

[0019] In a second aspect of the present application, an electrochemical device is also provided, including a negative electrode plate and a negative electrode tab, wherein the negative electrode plate includes a plate region and a tab region, the tab region is adjacent to the plate region, and the tab is connected to the tab region; the plate region and the tab region both include a lithium-containing alloy strip, the non-lithium element content in the lithium-containing alloy strip is m3, and the value range of m3 is 10wt%<m3<50wt%.

[0020] Optionally, the value range of m3 is 15wt%≤m3≤25wt%.

[0021] Optionally, the material used for the lithium-containing alloy strip includes any one of the alloys shown in Formula I;

[0022] Li-A 1 Formula I

[0023] Among them, A 1 The element is selected from at least one of Ag, Al, B, Mg, Au, Na, Si, Sn, Zn, Ba, Bi, C, Ca, Ge, Cs, Ga, K, Pb, P or Sb.

[0024] Optionally, the lithium-containing alloy strip includes any one of Li-Ag, Li-Al, Li-B, Li-Mg, Li-Au, Li-Na, Li-Si, Li-Sn, Li-Zn, Li-Ba, Li-Bi, Li-C, Li-Ca, Li-Ge, Li-Cs, Li-Ga, Li-K, Li-Pb, Li-P, Li-Sb, Li-B-Mg or Li-Mg-Si.

[0025] The third aspect of the present application also provides an electrochemical device, including a negative electrode plate and a negative electrode tab, wherein the negative electrode plate includes a plate region and a tab region, and the tab region is adjacent to the plate region; the plate region and the tab region both include a lithium-containing metal strip, the non-lithium element content in the lithium-containing metal strip is m1, and the value range of m1 is 0wt%≤m1≤10wt%; wherein a lithium alloy foil is arranged in the tab region; the non-lithium element content in the lithium alloy foil is m2, and the value range of m2 is 10wt%<m2<100wt%, and m1<m2, and the tab is connected to the lithium alloy foil.

[0026] Optionally, the lithium-containing metal strip includes a lithium strip or a lithium-containing alloy strip; the material used for the lithium-containing alloy strip includes any one of the alloys shown in Formula I;

[0027] Li-A 1 Formula I

[0028] The material used for the lithium alloy foil includes any one of the alloys shown in Formula II;

[0029] Li-A 2 Formula II

[0030] Among them, A 1 Elements and A 2 The element is independently selected from at least one of Ag, Al, B, Mg, Au, Na, Si, Sn, Zn, Ba, Bi, C, Ca, Ge, Cs, Ga, K, Pb, P or Sb.

[0031] Optionally, the lithium-containing alloy strip and the lithium alloy foil have the same alloy composition; or, the lithium-containing alloy strip and the lithium alloy foil have different alloy compositions.

[0032] Optionally, the A 1 The element is Mg; the A 2 The element is selected from at least one of Ag, Al, B, Mg, Au, Na, Si, Sn, Zn, Ba, Bi, C, Ca, Ge, Cs, Ga, K, Pb, P or Sb.

[0033] Optionally, the value range of m2 is 10wt%<m2≤30wt%.

[0034] Optionally, the lithium alloy foil is connected to a local position of the tab region;

[0035] Optionally, the connection width between the negative electrode tab and the lithium alloy foil is L1, and the width of the lithium alloy foil is L3;

[0036] The relationship between L1 and L3 satisfies the equation ii:

[0037] L1<L3 Formula ii

[0038] The value range of L3 is 1mm≤L3≤10mm.

[0039] Optionally, the thickness of the lithium alloy foil is d2, and the value range of d2 is 8 μm≤d2≤50 μm.

[0040] According to a fourth aspect of the present application, an electronic device is also provided, comprising the electrochemical device described in any one of the above items.

[0041] The beneficial effects of the technical solution provided by this application include at least:

[0042] The present invention aims to improve the energy density of the electrochemical device by directly using lithium-containing metal strips to prepare negative electrode plates, and then improve the hardness of the pole lug connection area by overall alloying (i.e., increasing the content of alloy components) or local differential alloying of the lithium-containing metal strips, or by locally reinforcing the pole lug area to further improve the connection reliability of the pole lug, significantly improve the breakage problem of the pole lug connection area during the cycle, and then improve the cycle performance of the electrochemical device, so that the electrochemical device has both high energy density and better cycle performance.

[0043] Pre-reinforcement of the tab connection area using a tab reinforcement device can improve connection reliability, thereby improving the cycle performance of the electrochemical device based on its high energy density.

[0044] The use of integral alloy negative electrode sheets or locally differentiated alloy negative electrode sheets to improve the hardness of the tab connection area can also improve the reliability of the tab connection on the basis of improving the energy density of the electrochemical device, improve the problem of tab connection area fracture during the cycle, and thus improve the cycle performance of the electrochemical device. In theory, the more alloy elements are added, the more the hardness is improved. Too low an alloy component may result in a low hardness of the lithium alloy strip, causing connection failure. Therefore, the amount of alloy component added to the integral alloy sheet or the amount of alloy component added to the locally differentiated lithium alloy foil must be greater than 10wt%.

[0045] By using a further preferred locally differentiated alloy negative electrode plate, controlling the alloy content of the lithium alloy strip in the plate area to 1-10wt%, and increasing the alloy content of the lithium alloy foil in the tab area to 10-100wt%, the stability of the tab connection can be enhanced, the cycle performance of the electrochemical device can be improved, and the electrochemical device can have a higher energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0047] Figure 1 After the negative electrode tab is connected in the prior art, cracks appear in the lithium belt near the connection area;

[0048] Figure 2 A top view of a solution for locally setting a reinforcement device for the negative electrode plate provided in the present application;

[0049] Figure 3 A cross-sectional view of a solution for locally setting a reinforcement device for the negative electrode plate provided in the present application (encapsulation setting);

[0050] Figure 4 A lithium strip product with a pre-installed tab reinforcement device provided in this application and a punching schematic diagram (fitting setting);

[0051] Figure 5 A top view of the locally differentially alloyed negative electrode sheet provided in this application;

[0052] Figure 6 This is a cross-sectional view of the locally differentially alloyed negative electrode sheet provided in this application (fitting arrangement). DETAILED DESCRIPTION

[0053] Electrochemical devices such as lithium metal batteries usually use lithium-coated copper foil as the negative electrode. The copper foil as the current collector greatly increases the weight of the lithium metal battery, which makes it difficult to further increase the energy density. Since lithium metal itself conducts electrons, the weight of the battery can be effectively reduced by directly using lithium-containing metal strips as the negative electrode of lithium metal batteries, thereby increasing the energy density. However, lithium metal is soft and has low hardness, and connection failure is prone to occur in the lug connection area. In addition, the volume of lithium metal batteries expands greatly during the charging and discharging process, and the lithium metal strip pole piece in the lug connection area is prone to breakage during multiple forced stretching processes, resulting in a decrease in cycle performance.

[0054] 1. Solution for local reinforcement of the tab area:

[0055] An electrochemical device comprises a negative electrode plate and a negative electrode tab, wherein the negative electrode plate comprises a plate region and a tab region, wherein the tab region is adjacent to the plate region; both the plate region and the tab region comprise a lithium-containing metal strip, wherein the lithium-containing metal strip contains non-lithium elements m1, and the value range of m1 is 0wt%≤m1≤10wt%; wherein a reinforcement device is arranged in the tab region; the reinforcement device is wrapped with metal foil, and the negative electrode tab is connected to the metal foil.

[0056] Specifically, the negative electrode includes a pole piece region and a lug region. The pole piece region is usually square (rectangular or square), and the lug region is usually also square, and the area of ​​the lug region is smaller than the area of ​​the pole piece region. For example, the short side of the lug region is connected to the long side of the pole piece region. Of course, the short side of the lug region can also be connected to the short side of the pole piece region, and this patent does not strictly limit it. The overall shape of the pole piece region and the lug region can be a "convex" shape, and the lug region is the convex part; of course, the overall shape of the pole piece region and the lug region can also include other irregular shapes. The pole piece region and the lug region are usually integrally formed, and the pole piece region and the lug region are obtained by cutting the lithium-containing metal strip.

[0057] The lithium-containing metal strip must contain lithium element. In addition, it may also contain other metal elements, such as Mg, Al, Na, Sn, Zn, Ba, Bi, Ca, Ge, Cs, Ga, K, Pb, Sb, etc. Of course, it may also contain some non-metallic elements, such as C, B, P, Si, etc.

[0058] The reinforcement device includes a metal foil, and the metal foil includes a non-lithium foil. In the metal foil, the content of a certain metal element is greater than 80wt%, and the main metal element can be selected from any one of Cu, Mg, Al, Ti, Fe, Ni, and Zn. The metal foil described in this patent may include a pure metal foil with a main metal content of more than 99wt%, such as Cu foil, Mg foil, and Al foil, and the content of the main element is more than 99wt%; the metal foil described in this patent also includes a non-lithium alloy foil (that is, the alloy foil does not contain lithium elements), as long as the content of the main element is greater than 80wt%, such as 5A06 aluminum alloy (Mg content 5.8wt% to 6.8wt%). The material used for the metal foil is preferably a material with high conductivity and good connection with the negative electrode tab, such as Cu foil.

[0059] The material of the tab may include Ni or Ni-Cu (nickel-plated copper) (unless otherwise specified, the "tab" in this application refers to the "negative tab").

[0060] The connection between the tab and the metal foil can be achieved by welding, gluing, or other methods known in the art. This patent does not make strict restrictions, as long as the tab can achieve the effect of flow diversion.

[0061] In some implementations, the lithium-containing metal ribbon includes a lithium ribbon (ie, a pure lithium metal ribbon), wherein the content of Li element in the lithium ribbon is greater than 99 wt %.

[0062] In some other embodiments, the lithium-containing metal strip includes a lithium-containing alloy strip, that is, an alloy composed of Li and other elements. The material used for the lithium-containing alloy strip includes any one of the alloys shown in Formula I;

[0063] Li-A 1 Formula I

[0064] Among them, A 1 The element is selected from at least one of Ag, Al, B, Mg, Au, Na, Si, Sn, Zn, Ba, Bi, C, Ca, Ge, Cs, Ga, K, Pb, P or Sb.

[0065] Preferably, the lithium-containing alloy ribbon includes any one of Li-Ag, Li-Al, Li-B, Li-Mg, Li-Au, Li-Na, Li-Si, Li-Sn, Li-Zn, Li-Ba, Li-Bi, Li-C, Li-Ca, Li-Ge, Li-Cs, Li-Ga, Li-K, Li-Pb, Li-P, Li-Sb, Li-B-Mg or Li-Mg-Si.

[0066] The lithium-containing alloy belt in this patent can be purchased commercially or obtained according to the preparation method in the prior art. For example, alloys such as Li-Mg and Li-Al can be purchased; Li-Ag alloy is prepared according to Song Jin, Yadong Ye, Yijie Niu, Yansong Xu, Hongchang Jin, Jinxi Wang, Zhaowei Sun, Anmin Cao, Xiaojun Wu, Yi Luo, Hengxing Ji, and Li-Jun Wan. Solid-Solution-Based Metal Alloy Phase for Highly Reversible Lithium Metal Anode. J. Am. Chem. Soc. 2020, 142, 8818-8826. Other alloy preparation methods can refer to this document. In the process of preparing the alloy, the metal Ag can be replaced with other metals.

[0067] In this patent, the metal foil is connected to the local position of the pole lug area. The metal foil is connected to the pole lug area in the following ways: it can be wrapped around the local position of the pole lug area; or the metal foil is attached to the local position of the pole lug area.

[0068] Specifically, "wrapping" means that the metal foil overlaps with the lithium-containing metal strip in the tab region in the thickness direction. For example, the metal foil may overlap with the thickness direction of one side of the tab region, or the metal foil may overlap with the thickness direction of both sides of the tab region. "Lamination" means that the metal foil only overlaps with the surface of the lithium-containing metal strip in the tab region, and does not overlap with the thickness direction of the tab region.

[0069] The metal foil can be located in the middle of the pole lug area, or can be located in the upper part of the pole lug area (ie, away from the pole sheet area), or located in the lower part of the pole lug area (ie, close to the pole sheet area). When located in the lower part of the pole lug area, the metal foil needs to be separated from the pole sheet area.

[0070] In this patent, the connection width between the tab and the reinforcement device is L1, and the width of the reinforcement device is L2; ​​the relationship between L1 and L2 satisfies the formula (i):

[0071] L1<L2 Formula Ⅰ

[0072] The value range of L2 is 1mm≤L2≤10mm.

[0073] Specifically, the width of the reinforcement device is the width of the metal foil, such as Figure 2 Similarly, the connection width between the tab and the reinforcing device is the distance in the y direction when the tab is connected to the tab region (not shown in the figure).

[0074] In this patent, the pole ear is connected to the metal foil of the pole ear area, and the connection width of the pole ear and the metal foil needs to be smaller than the width of the metal foil, that is, the pole ear connection area needs to be entirely located in the metal foil, otherwise (that is, at least part of the pole ear connection area is located on the lithium-containing metal belt in the pole ear area), even if the metal foil is provided on the pole ear area, the effect of high energy density and high cycle performance cannot be achieved. In some examples of this patent, each layer of the pole piece of the electrochemical device has a pole ear area, and the pole piece area and the pole ear area are integrally formed, and the two are obtained by cutting. Before the connection, the pole ear areas of all layers are stacked together, and the pole ear areas and the pole ears of all layers need to be connected together to derive current and supply power. In some examples of this patent, the metal foil (such as Cu foil) wraps all layers of the pole ear area, and then the pole ear is connected to the metal foil and welded into a whole; or the metal foil is attached to each layer of the pole ear area, and then the pole ear is connected to the metal foil, for example, the pole ear is connected to the outer metal foil or the pole ear is connected to the inner metal foil, and welded into a whole; no matter which method, the pole ear and the negative pole piece can be connected into a whole. There can be one or more tabs, which is not limited in this patent, and those skilled in the art can set them according to actual needs.

[0075] In this patent, the thickness of the metal foil is d1, and the value range of d1 is 8μm≤d1≤50μm. If the metal foil is too thick, the connection of the tab is not firm, and if the metal foil is too thin, it is easy to break, which will affect the energy density and cycle performance of the electrochemical device.

[0076] 2. Solution for overall alloying of negative electrode sheets

[0077] An electrochemical device comprises a negative electrode plate and a negative electrode tab, wherein the negative electrode plate comprises a plate region and a tab region, wherein the tab region is adjacent to the plate region; the tab is connected to the tab region; the plate region and the tab region both comprise a lithium-containing alloy strip, wherein the non-lithium element content of the lithium-containing alloy strip is m3, and the value range of m3 is 10wt%<m3<100wt%.

[0078] Specifically, the negative electrode pole piece includes a pole piece area and a lug area. The pole piece area is usually square (rectangular or square), and the lug area is usually also square, and the area of ​​the lug area is smaller than the area of ​​the pole piece area. For example, the short side of the lug area is connected to the long side of the pole piece area. Of course, the short side of the lug area can also be connected to the short side of the pole piece area, which is not strictly limited in this patent. The overall shape of the pole piece area and the lug area can be a convex shape, and the lug area is the convex part; of course, the overall shape of the pole piece area and the lug area can also include other irregular shapes. The pole piece area and the lug area are usually integrally formed, and the pole piece area and the lug area are obtained by cutting the lithium-containing metal strip.

[0079] The pole piece area and the pole ear area both include lithium-containing alloy strips, and the alloy component (non-lithium element) in the lithium-containing alloy strip needs to be greater than 10wt%. This can improve the hardness of the pole ear connection area, improve the connection reliability, improve the problem of fracture in the pole ear connection area during the cycle, and thus improve the cycle performance of the electrochemical device. In theory, the more alloy elements are added, the more the hardness is improved. If the alloy component is added too little, the hardness of the lithium-containing alloy strip may be low and difficult to use. Therefore, the amount of alloy component added is limited to greater than 10wt%.

[0080] Optionally, the value range of m3 is 15wt%≤m3≤25wt%. If the content of alloy components in the lithium-containing alloy strip is too high, the energy density and cycle performance will be affected; if the content is too low, it will not improve the hardness of the alloy and the connection.

[0081] For the pole tabs in this solution connected to the pole tab area, the pole tab areas can be stacked during the preparation of the electrochemical device, the pole tabs can be connected to the outer pole tab area, or the pole tabs can be connected to the inner pole tab area. This patent does not make strict limitations, as long as the pole tabs are connected to the pole tab area.

[0082] 3. Solutions for local differential alloying:

[0083] An electrochemical device comprises a negative electrode plate and a negative electrode tab, wherein the negative electrode plate comprises a plate region and a tab region, wherein the tab region is adjacent to the plate region; both the plate region and the tab region comprise a lithium-containing metal strip, wherein the content of non-lithium elements in the lithium-containing metal strip is m1, and the value range of m1 is 0wt%≤m1≤10wt%; wherein a reinforcing device lithium alloy foil is arranged in the tab region; the content of non-lithium elements in the lithium alloy foil is m2, and the value range of m2 is 10wt%<m2<100wt%, and m1<m2; and the negative electrode tab is connected to the lithium alloy foil.

[0084] In this solution, the electrode area and the ear area in the negative electrode are similar to those in Solution 1 and will not be described in detail here. The lithium-containing metal strip must contain lithium elements, and may also contain other metal elements, such as metal elements, non-metal elements, etc., which are similar to those in Solution 1 and will not be described in detail here.

[0085] The lithium-containing metal strip and the lithium alloy foil need to have different alloy contents. Specifically, the lithium-containing metal strip used as the pole piece area and the pole lug area may include a pure lithium strip, or a lithium-containing alloy strip with an alloy content (non-lithium element) ≤ 10wt%, while the lithium alloy foil located on the lithium-containing metal strip in the pole lug area has an alloy content of > 10wt%. That is, the alloy content in the lithium-containing alloy strip is very small or directly a pure lithium strip, while the alloy content in the lithium alloy foil located in the pole lug area needs to be higher, so that the alloy content of the two is differentiated.

[0086] When alloying the pole piece as a whole, the content of the alloy component must be at least >10wt%, and some lithium alloy pole pieces have their own preferred alloy component range. When the preferred alloy component range is not within this range (>10wt%), it will affect the cycle performance and limit the types of alloys used; and the alloy component content of the overall pole piece is >10wt%, because the excessively high alloy component content may affect the energy density. Therefore, only lithium alloy foil with high alloy content is used in the area connected to the pole lug, and lithium alloy with lower alloy component content is used in the rest of the area. This not only ensures that the cycle performance of the lithium alloy pole piece is further improved, but also reduces the alloy content as a whole, and improves the energy density of the electrochemical device.

[0087] In this patent, the lithium-containing metal strip includes a lithium strip or a lithium-containing alloy strip, and the material used for the lithium-containing alloy strip includes any one of the alloys shown in Formula I;

[0088] Li-A 1 Formula I

[0089] The material used for the lithium alloy foil includes any one of the alloys shown in Formula II;

[0090] Li-A 2 Formula II

[0091] Among them, A 1 Elements and A 2 The element is independently selected from at least one of Ag, Al, B, Mg, Au, Na, Si, Sn, Zn, Ba, Bi, C, Ca, Ge, Cs, Ga, K, Pb, P or Sb.

[0092] In this patent, the alloy composition of the lithium-containing alloy strip and the lithium alloy foil is the same; or, the alloy composition of the lithium-containing alloy strip and the lithium alloy foil is different.

[0093] Specifically, when the alloy composition of the lithium-containing alloy strip and the lithium alloy foil is the same, the element types of the two are the same, but the content of the elements is different, for example, the lithium-containing alloy strip is Li-5wt%Mg, and the lithium alloy foil is Li-20wt%Mg. When the alloy composition of the lithium-containing alloy strip and the lithium alloy foil is different, the element types and contents of the two are different, for example, the lithium-containing alloy strip is Li-5wt%Mg, and the lithium alloy foil is Li-20wt%Al; of course, this situation also includes that some elements may be the same, the lithium-containing alloy strip is Li-5wt%Mg, and the lithium alloy foil is Li-10wt%Mg-10wt%Si.

[0094] A preferred embodiment, said A 1 The element is Mg; the A 2 The element is selected from at least one of Ag, Al, B, Mg, Au, Na, Si, Sn, Zn, Ba, Bi, C, Ca, Ge, Cs, Ga, K, Pb, P or Sb. The preferred alloy composition range of Li-Mg alloy is 5wt% to 10wt%. Within this range, the alloy material has excellent cycle performance, and the pole piece uses an alloy with a low Mg content as a whole, and only uses lithium alloy foil with a high alloy content in the pole ear connection part, which can reduce the weight of the pole piece as a whole and effectively avoid unnecessary energy density loss.

[0095] Specifically, the pole piece region and the pole lug region include a lithium-containing alloy strip, which is Li-Mg, and the Mg content is 5wt%≤m1<10wt%. The lithium alloy foil arranged in the pole lug region includes Li-A 2 , A 2 The element is at least one selected from Ag, Al, B, Mg, Au, Na, Si, Sn, Zn, Ba, Bi, C, Ca, Ge, Cs, Ga, K, Pb, P or Sb, A 2 The content of the element is 10wt%<m2≤20wt%.

[0096] In another preferred embodiment, the lithium-containing metal strip includes a lithium strip, and the material used for the lithium alloy foil includes any one of the alloys shown in Formula II;

[0097] Li-A 2 Formula II

[0098] Among them, A 2 The elements independently include at least one of Ag, Al, B, Mg, Au, Na, Si, Sn, Zn, Ba, Bi, C, Ca, Ge, Cs, Ga, K, Pb, P or Sb.

[0099] Specifically, the pole piece region and the pole lug region include pure lithium strips, and the lithium alloy foil disposed in the pole lug region includes Li-A 2 , which not only enables the electrochemical device to have good cycle performance but also high energy density.

[0100] Preferably, the lithium alloy foil is connected to the tab region by wrapping the foil around a local portion of the tab region; or the lithium alloy foil is attached to a local portion of the tab region. Specifically, the meanings of "wrapping", "attaching" and "local portion" in this solution are similar to those in Solution 1 and will not be repeated here.

[0101] The connection width between the tab and the lithium alloy foil is L1, and the width of the lithium alloy foil is L3; the relationship between L1 and L3 satisfies the formula II:

[0102] L1<L3 Formula ii

[0103] The value range of L3 is 1mm≤L3≤10mm.

[0104] Specifically, the connection width L1 between the tab and the lithium alloy foil is similar to that in the first solution, and will not be described in detail here. The width L3 of the lithium alloy foil is similar to the thickness L2 of the metal foil in the first solution, which is the distance of the lithium alloy foil in the y direction, such as Figure 5 shown.

[0105] In this patent, the tab is connected to the lithium alloy foil in the tab area, and the connection width between the tab and the lithium alloy foil needs to be smaller than the width of the lithium alloy foil, that is, the tab connection area needs to be entirely located in the lithium alloy foil. When at least part of the tab connection area is located on the lithium-containing metal band in the tab area, even if a lithium alloy foil is provided on the tab area, the effects of high energy density and high cycle performance cannot be achieved.

[0106] In this patent, the thickness of the lithium alloy foil is d2, and the value range of d2 is 8μm≤d2≤50μm. If the alloy foil is too thick, the tab connection is not firm, and if the alloy foil is too thin, it is easy to break, which will affect the energy density and cycle performance of the electrochemical device.

[0107] The connection method between the tab and the lithium alloy foil is similar to the connection method between the tab and the metal foil in Scheme 1, and will not be repeated here.

[0108] Positive electrode:

[0109] In the present application, the positive electrode material layer includes a positive electrode active material. The present application has no particular restrictions on the positive electrode active material, as long as the purpose of the present application can be achieved, for example, it may include at least one of lithium or a composite oxide of a transition metal element. The present application has no particular restrictions on the above-mentioned transition metal elements, as long as the purpose of the present application can be achieved, for example, it may include at least one of nickel, manganese, cobalt or iron. Specifically, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate or lithium titanate.

[0110] Electrolyte:

[0111] The electrolyte of the present application may also include lithium salts and other non-aqueous solvents. The present application has no particular restrictions on the lithium salts, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB or lithium difluoroborate. Preferably, the lithium salt includes LiPF6.

[0112] The present application has no particular restrictions on other non-aqueous solvents, as long as the purpose of the present application can be achieved, for example, it may include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents. The above-mentioned carbonate compounds may include but are not limited to at least one of linear carbonate compounds, cyclic carbonate compounds or fluorinated carbonate compounds. The above-mentioned linear carbonate compounds may include but are not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or ethyl methyl carbonate (MEC). The above-mentioned cyclic carbonate may include but is not limited to at least one of propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound may include, but is not limited to, at least one of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The above-mentioned carboxylate compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decalactone, valerolactone, or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, cyclopentane, methyl cyclopentane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The content of the other non-aqueous solvents is not particularly limited, as long as the purpose of the present application can be achieved.

[0113] Electrochemical device:

[0114] The electrochemical device of the present application includes any device that generates an electrochemical reaction, and specific examples thereof include all kinds of primary batteries or secondary batteries. In particular, the electrochemical device is a lithium secondary battery.

[0115] In some embodiments, the electrochemical device of the present application includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte.

[0116] In some embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly through a winding process or a lamination process, or other processes in the art can be selected to make an electrode assembly. This application is not limited as long as the purpose of this application is achieved.

[0117] The electrochemical device of the present application also includes an outer package for packaging the electrode assembly. In some embodiments, the outer package can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc., or a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0118] Electronics:

[0119] The present application further provides an electronic device, which includes the electrochemical device according to the present application.

[0120] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0121] The core innovation of the present invention is to use the lithium-containing metal strip that is alloyed as a whole, or partially alloyed, or partially reinforced directly as the electrochemical negative electrode, which can significantly increase the energy density of the electrochemical device while improving the cycle performance. The local reinforcement of the lug area of ​​the lithium-containing metal strip can improve the problem of lug connection and lug connection area fracture during the cycle process. The present invention has high practical application value.

[0122] In the embodiments of this patent, the pure lithium strip is purchased from Zhongneng Lithium Industry with a purity of 99.9%;

[0123] Li-Mg alloy was purchased from Zhongneng Lithium Industry;

[0124] Li-Ag alloy preparation method reference: Song Jin, Yadong Ye, Yijie Niu, Yansong Xu, Hongchang Jin, Jinxi Wang, Zhaowei Sun, Anmin Cao, Xiaojun Wu, Yi Luo, Hengxing Ji, and Li-Jun Wan. Solid-Solution-Based Metal Alloy Phase for Highly Reversible Lithium Metal Anode. J. Am. Chem. Soc. 2020, 142, 8818-8826;

[0125] Li-1wt%Mg-8wt%B preparation method reference: Chen Wu, et al.Mg Doped Li–LiB Alloy with In Situ Formed Lithiophilic LiB Skeleton for Lithium Metal Batteries. Adv. Sci. 2020, 1902643;

[0126] Li-45wt%B alloy was purchased from Zhongneng Lithium Industry;

[0127] Li-5wt%Mg-25wt%B preparation method reference: Chen Wu, et al.Mg Doped Li–LiBAlloy with In Situ Formed Lithiophilic LiB Skeleton for Lithium Metal Batteries. Adv. Sci. 2020, 1902643;

[0128] Li-5wt%Mg-5wt%Si preparation method reference: Chen Wu, et al.Mg Doped Li–LiBAlloy with In Situ Formed Lithiophilic LiB Skeleton for Lithium Metal Batteries. Adv. Sci. 2020, 1902643;

[0129] "NMC811" refers to LiNi 0.8 Mn 0.1 Co 0.1 O2;

[0130] "SUS" alloy refers to stainless steel.

[0131] The following describes the performance evaluation of the lithium metal battery according to the embodiments, examples and comparative examples of the present application.

[0132] Example 1

[0133] (1) Preparation of negative electrode sheet

[0134] The 20 μm thick pure lithium strip is cut into the specifications of the pole piece area (40 mm×60 mm) and the pole lug area (5 mm×10 mm) for standby use, and the short side of the pole lug area is connected to the long side of the pole piece area.

[0135] (2) Preparation of positive electrode sheet

[0136] The positive electrode ternary active material NMC811, conductive carbon black (Super P), polyvinylidene fluoride (PVDF, molecular weight 180,000, the same as the following examples) are mixed in a weight ratio of 96:2:2, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 0.75 (i.e. 75wt%, the same as the following examples), and stirred evenly. The slurry is evenly coated on the positive electrode current collector aluminum foil and dried at 90°C to obtain a positive electrode sheet. After coating, the electrode sheet is cut into the specifications of the electrode sheet area (38mm×58mm) and the ear area (5mm×10mm) for standby use.

[0137] (3) Preparation of electrolyte

[0138] In a dry argon atmosphere, the organic solvent ethylene carbonate (EC) and 1,1,2,2-tetrafluoro-3-(1,1,2,2-tetrafluoroethoxy)propane (TTE) are first mixed in a mass ratio of EC:TTE=2:3, and then fluoroethylene carbonate (FEC), fluorodimethyl carbonate (FEMC) and lithium salt lithium hexafluorophosphate (LiPF6) are added to the organic solvent and dissolved and mixed evenly to obtain an electrolyte with a lithium salt concentration of 1.0M 1M LiPF6 in20% FEC+30% FEMC+20% EC+30% TTE.

[0139] (4) Preparation of lithium metal batteries

[0140] Polyethylene (PE) with a thickness of 15μm is selected as the isolation membrane, and a Z-shaped stacking method is adopted. The two sides of the diaphragm are the positive electrode and the negative electrode, and the isolation membrane is between the electrode pieces. After stacking, the pole ear (made of Ni) in the pole ear area is connected. Before connecting the pole ear, a layer of Cu foil with a width of 3mm and a thickness of 8μm is wrapped in the pole ear area. Then the pole ear and Cu foil are connected by welding. The width of the pole ear connection area is 2.5mm. After welding, the Cu foil is cut and trimmed, and then placed in the aluminum-plastic film. After top and side sealing, liquid injection, and packaging, a lithium metal battery is finally obtained.

[0141] Example 2

[0142] (1) Preparation of negative electrode sheet

[0143] The Cu foil is cut into thin strips with a width of 3mm and a thickness of 8μm. The thin strips of Cu foil are then rolled into the pure lithium strip to fit the pole piece containing the reinforcement device. Finally, the pole piece is cut into the specifications of the pole piece area (40mm×60mm) and the pole ear area (5mm×10mm) for use. The short side of the pole ear area is connected to the long side of the pole piece area. The thin strips of Cu foil are reserved in advance in the pole ear connection area.

[0144] (2) Preparation of positive electrode sheet

[0145] Same as Example 1

[0146] (3) Preparation of electrolyte

[0147] Same as Example 1

[0148] (4) Preparation of lithium metal batteries

[0149] Polyethylene (PE) with a thickness of 15μm is selected as the isolation membrane, and a Z-shaped stacking method is adopted. The positive electrode and the negative electrode are on both sides of the diaphragm, and the isolation membrane is between the electrode sheets. After stacking, the ear area (made of Ni) is connected. The ear is connected to the slender Cu foil by welding. The width of the ear connection area is 2.5mm, and then it is placed in the aluminum-plastic film. After top and side sealing, liquid injection, and packaging, a lithium metal battery is finally obtained.

[0150] Example 3

[0151] (1) Preparation of negative electrode sheet

[0152] Same as Example 1

[0153] (2) Preparation of positive electrode sheet

[0154] Same as Example 1

[0155] (3) Preparation of electrolyte

[0156] Same as Example 1

[0157] (4) Preparation of lithium metal batteries

[0158] Polyethylene (PE) with a thickness of 15μm is selected as the isolation membrane, and a Z-shaped stacking method is adopted. The two sides of the diaphragm are the positive electrode and the negative electrode, and the isolation membrane is between the electrode pieces. After stacking, the pole ear (made of Ni) in the pole ear area is connected. Before connecting the pole ear, a layer of Cu foil with a width of 3mm and a thickness of 5μm is wrapped in the pole ear connection area. Then the pole ear is connected to the Cu foil by welding. The width of the pole ear connection area is 2.5mm. After welding, the Cu foil is cut and trimmed, and then placed in the aluminum-plastic film. After top and side sealing, liquid injection, and packaging, a lithium metal battery is finally obtained.

[0159] Example 4

[0160] (1) Preparation of negative electrode sheet

[0161] Same as Example 1

[0162] (2) Preparation of positive electrode sheet

[0163] Same as Example 1.

[0164] (3) Preparation of electrolyte

[0165] Same as Example 1.

[0166] (4) Preparation of lithium metal batteries

[0167] Polyethylene (PE) with a thickness of 15μm is selected as the isolation membrane, and a Z-shaped stacking method is adopted. The positive electrode and the negative electrode are on both sides of the diaphragm, and the isolation membrane is between the electrode pieces. After stacking, the pole piece (made of Ni) in the pole piece area is connected. Before connecting the pole piece, a layer of Cu foil with a width of 3mm and a thickness of 10μm is wrapped in the pole piece connection area. Then the pole piece is connected to the Cu foil by welding. The width of the pole piece connection area is 2.5mm. After welding, the Cu foil is cut and trimmed, and then placed in the aluminum-plastic film. After top and side sealing, liquid injection, and packaging, a lithium metal battery is finally obtained.

[0168] Example 5

[0169] (1) Preparation of negative electrode sheet

[0170] Same as Example 1

[0171] (2) Preparation of positive electrode sheet

[0172] Same as Example 1

[0173] (3) Preparation of electrolyte

[0174] Same as Example 1

[0175] (4) Preparation of lithium metal batteries

[0176] Polyethylene (PE) with a thickness of 15μm is selected as the isolation membrane, and a Z-shaped stacking method is adopted. The positive electrode sheet and the negative electrode sheet are respectively on both sides of the diaphragm, and the isolation membrane is between the electrode sheets. After stacking, the ear tabs (made of Ni-Cu) in the ear area are connected. Before connecting the ear tabs, a layer of Cu foil with a width of 3mm and a thickness of 50μm is wrapped in the ear tab connection area. Then the ear tab is connected to the Cu foil by welding. The width of the ear tab connection area is 2.5mm. After welding, the Cu foil is cut and trimmed, and then placed in the aluminum-plastic film. After top and side sealing, liquid injection, and packaging, a lithium metal battery is finally obtained.

[0177] Example 6

[0178] (1) Preparation of negative electrode sheet

[0179] Same as Example 1

[0180] (2) Preparation of positive electrode sheet

[0181] Same as Example 1

[0182] (3) Preparation of electrolyte

[0183] Same as Example 1

[0184] (4) Preparation of lithium metal batteries

[0185] Polyethylene (PE) with a thickness of 15μm is selected as the isolation membrane, and a Z-shaped stacking method is adopted. The positive electrode sheet and the negative electrode sheet are respectively on both sides of the diaphragm, and the isolation membrane is between the electrode sheets. After stacking, the ear tabs (made of Ni-Cu) in the ear area are connected. Before connecting the ear tabs, a layer of Cu foil with a width of 3mm and a thickness of 100μm is wrapped in the ear tab connection area. Then the ear tab is connected to the Cu foil by welding. The width of the ear tab connection area is 2.5mm. After welding, the Cu foil is cut and trimmed, and then placed in the aluminum-plastic film. After top and side sealing, liquid injection, and packaging, a lithium metal battery is finally obtained.

[0186] Example 7

[0187] (1) Preparation of negative electrode sheet

[0188] Same as Example 1

[0189] (2) Preparation of positive electrode sheet

[0190] Same as Example 1

[0191] (3) Preparation of electrolyte

[0192] Same as Example 1

[0193] (4) Preparation of lithium metal batteries

[0194] Polyethylene (PE) with a thickness of 15μm is selected as the isolation membrane, and a Z-shaped stacking method is adopted. The two sides of the diaphragm are the positive electrode and the negative electrode, and the isolation membrane is between the electrode pieces. After stacking, the pole ear (made of Ni) in the pole ear area is connected. Before connecting the pole ear, a layer of Cu foil with a width of 2mm and a thickness of 8μm is wrapped in the pole ear connection area. Then the pole ear is connected to the Cu foil by welding. The width of the pole ear connection area is 2.5mm. After welding, the Cu foil is cut and trimmed, and then placed in the aluminum-plastic film. After top and side sealing, liquid injection, and packaging, a lithium metal battery is finally obtained.

[0195] Example 8

[0196] (1) Preparation of negative electrode sheet

[0197] Same as Example 1

[0198] (2) Preparation of positive electrode sheet

[0199] Same as Example 1

[0200] (3) Preparation of electrolyte

[0201] Same as Example 1

[0202] (4) Preparation of lithium metal batteries

[0203] Polyethylene (PE) with a thickness of 15μm is selected as the isolation membrane, and a Z-shaped stacking method is adopted. The two sides of the diaphragm are the positive electrode and the negative electrode, and the isolation membrane is between the electrode pieces. After stacking, the pole ear (made of Ni) in the pole ear area is connected. Before connecting the pole ear, a layer of Cu foil with a width of 5mm and a thickness of 8μm is wrapped in the pole ear connection area. Then the pole ear is connected to the Cu foil by welding. The width of the pole ear connection area is 2.5mm. After welding, the Cu foil is cut and trimmed, and then placed in the aluminum-plastic film. After top and side sealing, liquid injection, and packaging, a lithium metal battery is finally obtained.

[0204] Example 9

[0205] (1) Preparation of negative electrode sheet

[0206] Same as Example 1

[0207] (2) Preparation of positive electrode sheet

[0208] Same as Example 1

[0209] (3) Preparation of electrolyte

[0210] Same as Example 1

[0211] (4) Preparation of lithium metal batteries

[0212] Polyethylene (PE) with a thickness of 15μm is selected as the isolation membrane, and a Z-shaped stacking method is adopted. The positive electrode sheet and the negative electrode sheet are respectively on both sides of the diaphragm, and the isolation membrane is between the electrode sheets. After stacking, the ear tabs (made of Ni) in the ear area are connected. Before connecting the ear tabs, a layer of Al foil with a width of 3mm and a thickness of 10μm is wrapped in the ear tab connection area. Then the ear tab is connected to the Al foil by welding. The width of the ear tab connection area is 2.5mm. After welding, the Al foil is cut and trimmed, and then placed in the aluminum-plastic film. After top and side sealing, liquid injection, and packaging, a lithium metal battery is finally obtained.

[0213] Example 10

[0214] (1) Preparation of negative electrode sheet

[0215] Same as Example 1

[0216] (2) Preparation of positive electrode sheet

[0217] Same as Example 1

[0218] (3) Preparation of electrolyte

[0219] Same as Example 1

[0220] (4) Preparation of lithium metal batteries

[0221] Polyethylene (PE) with a thickness of 15μm is selected as the isolation membrane, and a Z-shaped stacking method is adopted. The two sides of the diaphragm are the positive electrode sheet and the negative electrode sheet, and the isolation membrane is between the electrode sheets. After stacking, the pole ear (made of Ni) in the pole ear area is connected. Before connecting the pole ear, a layer of Mg foil with a width of 3mm and a thickness of 10μm is wrapped in the pole ear connection area. Then the pole ear is connected to the Mg foil by welding. The width of the pole ear connection area is 2.5mm. After welding, the Mg foil is cut and trimmed, and then placed in the aluminum-plastic film. After top and side sealing, liquid injection, and packaging, a lithium metal battery is finally obtained.

[0222] Embodiment 11

[0223] (1) Preparation of negative electrode sheet

[0224] The 20 μm thick Li-5wt% Mg alloy is cut into the specifications of the pole piece area (40 mm×60 mm) and the pole lug area (5 mm×10 mm) for use, and the short side of the pole lug area is connected to the long side of the pole piece area.

[0225] (2) Preparation of positive electrode sheet

[0226] Same as Example 1

[0227] (3) Preparation of electrolyte

[0228] Same as Example 1

[0229] (4) Preparation of lithium metal batteries

[0230] Same as Example 1

[0231] Embodiment 112

[0232] (1) Preparation of negative electrode sheet

[0233] The 20 μm thick Li-5wt% Ag alloy is cut into the specifications of the pole piece region (40 mm×60 mm) and the pole lug region (5 mm×10 mm) for standby use, and the short side of the pole lug region is connected to the long side of the pole piece region.

[0234] (2) Preparation of positive electrode sheet

[0235] Same as Example 1

[0236] (3) Preparation of electrolyte

[0237] Same as Example 1

[0238] (4) Preparation of lithium metal batteries

[0239] Same as Example 1

[0240] Embodiment 13

[0241] (1) Preparation of negative electrode sheet

[0242] The 20 μm thick Li-1wt% Mg-8wt% B alloy is cut into the specifications of the pole piece area (40mm×60mm) and the pole ear area (5mm×10mm) for use, and the short side of the pole ear area is connected to the long side of the pole piece area.

[0243] (2) Preparation of positive electrode sheet

[0244] Same as Example 1

[0245] (3) Preparation of electrolyte

[0246] Same as Example 1

[0247] (4) Preparation of lithium metal batteries

[0248] Same as Example 1

[0249] Embodiment 14

[0250] (1) Preparation of negative electrode sheet

[0251] The 20 μm thick pure lithium ribbon was cut into the specifications of the pole piece area (40 mm×60 mm) for later use. The specifications of the pole lug area were the same as those of Comparative Example 1.

[0252] (2) Preparation of positive electrode sheet

[0253] Same as Example 1

[0254] (3) Preparation of electrolyte

[0255] Same as Example 1

[0256] (4) Preparation of lithium metal batteries

[0257] Polyethylene (PE) with a thickness of 15μm is selected as the isolation membrane, and a Z-shaped stacking method is adopted. The positive electrode sheet and the negative electrode sheet are respectively on both sides of the diaphragm, and the isolation membrane is between the electrode sheets. After stacking, the pole ears are connected at the pole ears. Before connecting the pole ears, a layer of Ti foil with a width of 3mm and a thickness of 10μm is wrapped in the pole ear connection area. Then the pole ear is connected to the Al foil by welding. The width of the pole ear connection area is 2.5mm. After welding, the Ti foil is cut and trimmed, and then placed in the aluminum-plastic film. After top and side sealing, liquid injection, and packaging, a lithium metal battery is finally obtained.

[0258] Example 14

[0259] (1) Preparation of negative electrode sheet

[0260] The 20 μm thick pure lithium strip was cut into (40 mm×60 mm) specifications for later use. The specifications of the tab area were the same as those of Comparative Example 1.

[0261] (2) Preparation of positive electrode sheet

[0262] Same as Example 1

[0263] (3) Preparation of electrolyte

[0264] Same as Example 1

[0265] (4) Preparation of lithium metal batteries

[0266] Polyethylene (PE) with a thickness of 15 μm is selected as the separator, and a Z-shaped stacking method is adopted. The positive electrode and the negative electrode are respectively on both sides of the separator, and the separator is between the electrode pieces. After stacking, the pole pieces are connected at the pole pieces. Before connecting the pole pieces, the pole piece connection area is wrapped with a layer of SUS foil with a width of 3 mm and a thickness of 10 μm (the specific composition of the SUS foil is: by weight percentage, carbon 0.08%, silicon 1.00%, chromium 20.00%, manganese 2.00%, nickel 11.00%, phosphorus 0.045%, sulfur 0.030%, and the rest is Fe). After that, the pole piece is connected to the SUS foil by welding. The width of the pole piece connection area is 2.5 mm. After welding, the SUS foil is cut and trimmed, and then placed in the aluminum-plastic film. After top and side sealing, liquid injection, and packaging, a lithium metal battery is finally obtained.

[0267] Embodiment 15

[0268] (1) Preparation of negative electrode sheet

[0269] The 20 μm thick Li-5 wt % Mg ribbon was cut into the same specifications as in Example 1.

[0270] (2) Preparation of positive electrode sheet

[0271] Same as Example 1

[0272] (3) Preparation of electrolyte

[0273] Same as Example 1

[0274] (4) Preparation of lithium metal batteries

[0275] A polyethylene (PE) with a thickness of 15 μm is selected as the separator, and a Z-shaped stacking method is adopted. The positive electrode and the negative electrode are on both sides of the separator, and the separator is between the electrodes. After stacking, the upper ear is directly welded on the ear area. After welding the ear, it is placed in the aluminum-plastic film, and after top and side sealing, liquid injection, and packaging, a lithium metal battery is finally obtained.

[0276] Example 16

[0277] (1) Preparation of negative electrode sheet

[0278] The 20 μm thick Li-10 wt % Mg ribbon was cut into the same specifications as in Example 1.

[0279] (2) Preparation of positive electrode sheet

[0280] Same as Example 1

[0281] (3) Preparation of electrolyte

[0282] Same as Example 1

[0283] (4) Preparation of lithium metal batteries

[0284] Same as Example 15

[0285] Embodiment 17

[0286] (1) Preparation of negative electrode sheet

[0287] The 20 μm thick Li-20 wt % Mg ribbon was cut into the same specifications as in Example 1.

[0288] (2) Preparation of positive electrode sheet

[0289] Same as Example 1

[0290] (3) Preparation of electrolyte

[0291] Same as Example 1

[0292] (4) Preparation of lithium metal batteries

[0293] Same as Example 15

[0294] Embodiment 18

[0295] (1) Preparation of negative electrode sheet

[0296] The 20 μm thick Li-20 wt % Ag tape was cut into the same specifications as in Example 1.

[0297] (2) Preparation of positive electrode sheet

[0298] Same as Example 1

[0299] (3) Preparation of electrolyte

[0300] Same as Example 1

[0301] (4) Preparation of lithium metal batteries

[0302] Same as Example 15

[0303] Embodiment 19

[0304] (1) Preparation of negative electrode sheet

[0305] The 20 μm thick Li-45 wt % B tape was cut into the same specifications as in Example 1.

[0306] (2) Preparation of positive electrode sheet

[0307] Same as Example 1

[0308] (3) Preparation of electrolyte

[0309] Same as Example 1

[0310] (4) Preparation of lithium metal batteries

[0311] Same as Example 15

[0312] Embodiment 20

[0313] (1) Preparation of negative electrode sheet

[0314] The 20 μm thick Li-5 wt % Mg-25 wt % B tape was cut into the same specifications as in Example 1.

[0315] (2) Preparation of positive electrode sheet

[0316] Same as Example 1

[0317] (3) Preparation of electrolyte

[0318] Same as Example 1

[0319] (4) Preparation of lithium metal batteries

[0320] Same as Example 15

[0321] Embodiment 21

[0322] (1) Preparation of negative electrode sheet

[0323] The 20 μm thick Li-5 wt % Mg ribbon was cut into the same specifications as in Example 1.

[0324] (2) Preparation of positive electrode sheet

[0325] Same as Example 1

[0326] (3) Preparation of electrolyte

[0327] Same as Example 1

[0328] (4) Preparation of lithium metal batteries

[0329] Polyethylene (PE) with a thickness of 15μm is selected as the isolation membrane, and a Z-shaped stacking method is adopted. The two sides of the diaphragm are the positive electrode sheet and the negative electrode sheet, and the isolation membrane is between the electrode sheets. After stacking, the pole ears (made of Ni) in the pole ear area are connected. Before connecting the pole ears, a layer of Li-20wt% Mg tape with a width of 3mm and a thickness of 10μm is wrapped in the pole ear connection area. After that, the pole ears are connected to the Li-20wt% Mg tape by welding. The width of the pole ear connection area is 2.5mm. After welding, the Li-20wt% Mg tape is cut and trimmed, and then placed in the aluminum-plastic film. After top and side sealing, liquid injection, and packaging, a lithium metal battery is finally obtained.

[0330] Embodiment 22

[0331] (1) Preparation of negative electrode sheet

[0332] The 15μm Li-20wt%Mg alloy strip (i.e., lithium alloy foil) is cut into 3mm wide strips, and then the Li-20wt%Mg alloy strip is rolled into a 20μm thick Li-5wt%Mg alloy strip (i.e., lithium-containing alloy strip) to form a locally differentially alloyed Li-Mg alloy strip. Finally, the pole piece is cut into the specifications of the pole piece area (40mm×60mm) and the pole ear area (5mm×10mm) for standby use, and the short side of the pole ear area is connected to the long side of the pole piece area. The part with a higher Mg content is reserved in advance in the pole ear connection area.

[0333] (2) Preparation of positive electrode sheet

[0334] Same as Example 1

[0335] (3) Preparation of electrolyte

[0336] Same as Example 1

[0337] (4) Preparation of lithium metal batteries

[0338] A polyethylene (PE) with a thickness of 15 μm is selected as the separator, and a Z-shaped stacking method is adopted. The positive electrode and the negative electrode are on both sides of the separator, and the separator is between the electrodes. After stacking, the pole ears are welded in the pole ear area, and the pole ears and the lithium alloy foil with a high Mg content are connected by welding. Then it is placed in an aluminum-plastic film, and after top and side sealing, liquid injection, and packaging, a lithium metal battery is finally obtained.

[0339] Embodiment 23

[0340] (1) Preparation of negative electrode sheet

[0341] The Li-20wt% Mg alloy strip in Example 21 is replaced by a Li-10wt% Al alloy strip, and the Li-5wt% Mg alloy strip is replaced by a Li-8wt% Mg alloy strip. The rest is the same as Example 21.

[0342] (2) Preparation of positive electrode sheet

[0343] Same as Example 1

[0344] (3) Preparation of electrolyte

[0345] Same as Example 1

[0346] (4) Preparation of lithium metal batteries

[0347] Same as Example 21.

[0348] Embodiment 24

[0349] (1) Preparation of negative electrode sheet

[0350] The Li-20wt% Mg alloy strip in Example 21 is replaced by a Li-25wt% B alloy strip, and the Li-5wt% Mg alloy strip is replaced by a Li-10wt% Mg alloy strip, and the rest is the same as Example 21.

[0351] (2) Preparation of positive electrode sheet

[0352] Same as Example 1

[0353] (3) Preparation of electrolyte

[0354] Same as Example 1

[0355] (4) Preparation of lithium metal batteries

[0356] Same as Example 21.

[0357] Embodiment 25

[0358] (1) Preparation of negative electrode sheet

[0359] The Li-20wt% Mg alloy strip in Example 21 is replaced by a Li-25wt% B-5wt% Mg alloy strip, and the Li-5wt% Mg alloy strip is replaced by a Li-5wt% Mg alloy strip. The rest is the same as Example 21.

[0360] (2) Preparation of positive electrode sheet

[0361] Same as Example 1

[0362] (3) Preparation of electrolyte

[0363] Same as Example 1

[0364] (4) Preparation of lithium metal batteries

[0365] Same as Example 21.

[0366] Embodiment 26

[0367] (1) Preparation of negative electrode sheet

[0368] The Li-20wt% Mg alloy strip in Example 21 is replaced by a Li-20wt% Ag alloy strip, and the Li-5wt% Mg alloy strip is replaced by a pure lithium strip. The rest is the same as Example 21.

[0369] (2) Preparation of positive electrode sheet

[0370] Same as Example 1

[0371] (3) Preparation of electrolyte

[0372] Same as Example 1

[0373] (4) Preparation of lithium metal batteries

[0374] Same as Example 21.

[0375] Embodiment 27

[0376] (1) Preparation of negative electrode sheet

[0377] The Li-20wt% Mg alloy strip in Example 21 is replaced by a Li-5wt% Mg-5wt% Si alloy strip, and the Li-5wt% Mg alloy strip is replaced by a Li-5wt% Mg alloy strip. The rest is the same as Example 21.

[0378] (2) Preparation of positive electrode sheet

[0379] Same as Example 1

[0380] (3) Preparation of electrolyte

[0381] Same as Example 1

[0382] (4) Preparation of lithium metal batteries

[0383] Same as Example 21.

[0384] Comparative Example 1

[0385] (1) Preparation of negative electrode sheet

[0386] The lithium-coated copper strip is cut into the specifications of the pole area (40mm×60mm) for use, in which the lithium strip layer thickness is 20μm and the copper foil thickness is 10μm. The specifications of the pole lug area (5mm×10mm) are for use, and the pole lug area is an empty copper foil without lithium layer coverage, and the short side of the pole lug area is connected to the long side of the pole area.

[0387] (2) Preparation of positive electrode sheet

[0388] Same as Example 1

[0389] (3) Preparation of electrolyte

[0390] Same as Example 1

[0391] (4) Preparation of lithium metal batteries

[0392] A polyethylene (PE) with a thickness of 15 μm is selected as the separator, and a Z-shaped stacking method is adopted. The positive electrode and the negative electrode are on both sides of the separator, and the separator is between the electrodes. After stacking, the pole ears are directly welded in the ear area. After connection, it is placed in an aluminum-plastic film, and after top and side sealing, liquid injection, and packaging, a lithium metal battery is finally obtained.

[0393] Comparative Example 2

[0394] (1) Preparation of negative electrode sheet

[0395] The lithium-coated porous copper strip was cut into the specifications of the electrode area (40 mm×60 mm) for standby use. The lithium layer thickness of the lithium-coated porous copper strip was 20 μm, the copper foil thickness was 10 μm, and the opening rate was 50%. The specifications of the electrode tab area were the same as those of Comparative Example 1.

[0396] (2) Preparation of positive electrode sheet

[0397] Same as Example 1

[0398] (3) Preparation of electrolyte

[0399] Same as Example 1

[0400] (4) Preparation of lithium metal batteries

[0401] Same as comparative example 1

[0402] Comparative Example 3 (no reinforcement)

[0403] The preparation method is similar to that of Example 1, except that no Cu foil reinforcement device is provided in the tab connection area.

[0404] Specifically, in step (4), after the positive electrode sheet, the negative electrode sheet and the separator are stacked as in Example 1, the tab is welded to the pure lithium strip in the tab area.

[0405] Energy density test:

[0406] Adopt 9th generation Neware test.

[0407] Cycle performance test:

[0408] The 9th generation Neware test was used: at 25°C, the lithium metal battery was allowed to stand for 5 minutes, charged to 4.3V at a constant current of 0.3C, and then charged at a constant voltage to a current of 0.025C; after the lithium metal battery was allowed to stand for 5 minutes, it was discharged to 2.8V at a constant current of 0.5C and allowed to stand for 5 minutes. This was a cyclic charge and discharge process. The above steps were repeated to cyclically charge and discharge the lithium metal battery.

[0409] The effectiveness of the scheme is evaluated by comparing the number of cycles of lithium metal batteries under the same capacity retention. The following table data involves two types of capacity retention, 80% and 88%, corresponding to two failure modes of the battery. 88% capacity retention corresponds to the normal capacity decay to 88%, and no welding failure occurs. 80% capacity retention corresponds to the battery having welding failure, and the capacity dives below 80% at a certain number of cycles.

[0410] See the table below for specific data:

[0411]

[0412] By comparing the examples and comparative examples in the table, it can be seen that the use of pure lithium strips or lithium-containing alloy strips to prepare negative electrode plates and the provision of a reinforcement device in the tab area can greatly improve the energy density and cycle performance of lithium metal batteries. The preferred solution is the local differential alloying design of the negative electrode plates in Examples 22-27, that is, the Li-Mg alloy strip is selected in the plate area, and a lithium alloy foil is provided in the tab area as a reinforcement device, and the lithium metal battery has better cycle performance and higher energy density.

[0413] Examples 1-6 and 8-13 illustrate that providing a reinforcement device including a metal foil in the tab area can ensure that the tab connection area has good stability during the battery cycle, thereby improving the battery cycle performance of lithium metal and ensuring that the lithium metal battery has a higher energy density.

[0414] Examples 1-6 illustrate that there is an optimal thickness (8-50 um) for the reinforcement device provided in the tab region. If the metal foil is too thin or too thick, it may affect the connection reliability and the cycle performance of the lithium metal battery.

[0415] Examples 3, 7 and 8 illustrate that there is an optimal width of the reinforcement device provided in the tab region, which is mainly related to the connection width between the tab and the reinforcement device. The width of the reinforcement device needs to be greater than the connection width between the tab and the reinforcement device, which can ensure that the lithium metal battery has better cycle performance and higher energy density. If the width of the reinforcement device is too narrow, the connection area between the tab and the reinforcement device falls outside the reinforcement device, affecting the reinforcement effect (not conducive to cycle performance), and if it is too wide, it may affect the energy density of the lithium metal battery.

[0416] Examples 4, 9-10, and 14 illustrate that the metal foil of the reinforcement device can be made of a variety of materials, such as Cu foil, Al foil, Mg foil, and Ti foil, all of which can improve the connection effect and improve the cycle performance of the lithium metal battery on the basis of the high energy density of the lithium metal battery.

[0417] Examples 15-20 illustrate that, in the overall alloying scheme, adding alloying elements can increase the pole piece hardness, improve the connection reliability, and improve the cycle performance of the lithium metal battery, while having better cycle performance and higher energy density.

[0418] Comparative Examples 1-2 show that when the negative electrode plate uses lithium-rich copper foil or perforated copper foil but no reinforcement device is provided in the tab connection area, the energy density of the lithium metal battery is low.

[0419] Comparative Example 3 shows that when lithium ribbon is directly used as the negative electrode plate, although the energy density of the lithium metal battery is high, the connection reliability is poor and the cycle performance is seriously deteriorated because no reinforcement device is set in the tab connection area.

[0420] The embodiments described above are merely preferred embodiments of the present application and are not intended to limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements made to the technical solutions of the present application by ordinary technicians in this field should fall within the protection scope determined by the claims of the present application.

Claims

1. An electrochemical device, comprising a negative electrode sheet and a negative electrode tab, characterized in that: The negative electrode plate comprises a plate region and a tab region; the tab region is adjacent to the plate region; The pole piece region and the pole ear region both include lithium-containing metal strips, the non-lithium element content in the lithium-containing metal strips is m1, and the value range of m1 is 0wt%≤m1≤10wt%; Wherein, the tab area is provided with a reinforcement device, and the reinforcement device comprises a metal foil; The negative electrode tab is connected to the metal foil, the metal foil is connected to a local position of the tab area, and the metal foil is spaced apart from the electrode area; Along the y direction, the connection width between the negative electrode tab and the metal foil is smaller than the width of the metal foil, and the y direction is the width direction of the metal foil; The metal foil includes any one of Cu foil, Mg foil, Al foil or Ti foil; The lithium-containing metal belt includes a lithium belt or a lithium-containing alloy belt, and the material used for the lithium-containing alloy belt includes any one of the alloys shown in Formula I; Li-A 1 Formula Ⅰ Among them, A 1 The element is selected from at least one of Ag, Al, B, Mg, Au, Na, Si, Sn, Zn, Ba, Bi, C, Ca, Ge, Cs, Ga, K, Pb, P or Sb.

2. The electrochemical device according to claim 1, which satisfies at least one of the following conditions; Condition 1: The lithium-containing alloy strip includes any one of Li-Ag, Li-Al, Li-B, Li-Mg, Li-Au, Li-Na, Li-Si, Li-Sn, Li-Zn, Li-Ba, Li-Bi, Li-C, Li-Ca, Li-Ge, Li-Cs, Li-Ga, Li-K, Li-Pb, Li-P, Li-Sb, Li-B-Mg or Li-Mg-Si; Condition 2: The width of the reinforcement device is L2, and the value range of L2 is 1mm≤L2≤10mm; Condition 3: The thickness of the metal foil is d1, and the value range of d1 is 8 μm≤d1≤50 μm.

3. An electrochemical device, comprising a negative electrode sheet and a negative electrode tab, characterized in that: The negative electrode pole piece includes a pole piece area and a pole ear area, the pole ear area is adjacent to the pole piece area, the pole piece area and the pole ear area are integrally formed; the negative electrode pole ear is connected to the pole ear area; The pole piece region and the pole ear region are both lithium-containing alloy strips, and the non-lithium element content in the lithium-containing alloy strip is m3, and the value range of m3 is 10wt%<m3<50wt%; The lithium-containing alloy strip includes any one of Li-Ag, Li-Al, Li-B, Li-Mg, Li-Au, Li-Na, Li-Si, Li-Sn, Li-Zn, Li-Ba, Li-Bi, Li-C, Li-Ca, Li-Ge, Li-Cs, Li-Ga, Li-K, Li-Pb, Li-P, Li-Sb, Li-B-Mg or Li-Mg-Si.

4. The electrochemical device according to claim 3, characterized in that The value range of m3 is 15wt%≤m3≤25wt%.

5. An electrochemical device, comprising a negative electrode sheet and a negative electrode tab, characterized in that: The negative electrode plate comprises a plate region and a tab region, wherein the tab region is adjacent to the plate region; The pole piece region and the pole ear region both include lithium-containing metal strips, the non-lithium element content in the lithium-containing metal strips is m1, and the value range of m1 is 0wt%≤m1≤10wt%; Wherein, the tab region is provided with a reinforcement device, and the reinforcement device comprises a lithium alloy foil; The non-lithium element content in the lithium alloy foil is m2, and the value range of m2 is 10wt%<m2<100wt%; And m1<m2; The negative electrode tab is connected to the lithium alloy foil, and the lithium alloy foil is connected to a local position of the tab area; the lithium alloy foil is spaced apart from the electrode area; The connection width between the negative electrode tab and the lithium alloy foil is L1, and the width of the lithium alloy foil is L3; The relationship between L1 and L3 satisfies the equation ii: L1<L3Formula ii The lithium-containing metal belt includes a lithium belt or a lithium-containing alloy belt, and the material used for the lithium-containing alloy belt includes any one of the alloys shown in Formula I; Li-A 1 Formula Ⅰ The material used for the lithium alloy foil includes any one of the alloys shown in Formula II; Li-A 2 Formula II Among them, A 1 Elements and A 2 The element is independently selected from at least one of Ag, Al, B, Mg, Au, Na, Si, Sn, Zn, Ba, Bi, C, Ca, Ge, Cs, Ga, K, Pb, P or Sb.

6. The electrochemical device according to claim 5, which satisfies at least one of the following conditions; Condition a: A 1 The element is Mg; The A 2 The element is selected from at least one of Ag, Al, B, Mg, Au, Na, Si, Sn, Zn, Ba, Bi, C, Ca, Ge, Cs, Ga, K, Pb, P and Sb; Condition b: the value range of m2 is 10wt%<m2≤30wt%; Condition c: The value range of L3 is 1mm≤L3≤10mm; Condition d: The thickness of the lithium alloy foil is d2, and the value range of d2 is 8 μm≤d2≤50 μm.

7. An electronic device comprising the electrochemical device according to any one of claims 1 to 6.

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