A negative electrode sheet and a battery

Abstract

The present application provides a negative electrode sheet and a battery. The negative electrode sheet includes a negative electrode current collector, an active coating, and an insulating layer. The negative electrode current collector, the active coating, and the insulating layer are sequentially stacked, and the active coating is located between the negative electrode current collector and the insulating layer. The active coating is a porous structure coating. The negative electrode sheet provided by the embodiment of the present application utilizes the setting of the active coating with a porous structure to release the stress generated during the charge and discharge process of the battery for forming lithium dendrites, so as to inhibit the growth of lithium dendrites on the negative electrode sheet, avoid the situation that the lithium dendrites pierce the separator, and improve the safety of the battery.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to a negative electrode sheet and a battery. Background Art

[0002] Since lithium metal batteries entered the market, they have been widely used due to their advantages such as long life, high specific capacity, and no memory effect.

[0003] In applications, it is found that since the negative electrode of a lithium metal battery uses lithium metal, lithium dendrites (i.e., strip-shaped metallic lithium crystals formed by the inactivation of active lithium in the battery) are likely to form on the negative electrode of the lithium metal battery. This not only reduces the active lithium inside the battery, thereby resulting in a low Coulomb efficiency of the battery (i.e., an irreversible reduction in the battery capacity); but also pierces the separator and causes a series of safety problems.

[0004] As can be seen from the above, the battery prepared based on the related technology has poor safety. Summary of the Invention

[0005] The purpose of the embodiments of this application is to provide a negative electrode sheet and a battery, which are used to solve the problem of poor safety of the battery prepared by the related technology.

[0006] In a first aspect, the embodiments of this application provide a negative electrode sheet, including:

[0007] A negative electrode current collector, and an active coating and an insulating layer provided on at least one side of the negative electrode current collector;

[0008] The negative electrode current collector, the active coating, and the insulating layer are sequentially stacked, and the active coating is located between the negative electrode current collector and the insulating layer; the active coating is a porous structure coating.

[0009] Optionally, the active coating includes a two-dimensional material, a network construction material, a catalytic material, and a conductive agent, and the two-dimensional material and the network construction material form the porous structure.

[0010] Optionally, the mass proportion of the two-dimensional material in the active coating is greater than or equal to 50% and less than or equal to 70%;

[0011] The mass proportion of the network construction material in the active coating is greater than or equal to 10% and less than or equal to 30%;

[0012] The mass proportion of the catalytic material in the active coating is greater than or equal to 3% and less than or equal to 7%.

[0013] Optionally, the two-dimensional material includes at least one of two-dimensional carbides and nitrides, graphene, porous graphene, porous two-dimensional carbides and nitrides, two-dimensional lamellar metal oxides, metal hydroxides, and metal sulfides.

[0014] Optionally, the network construction material includes at least one of carbon nanotubes, multi-walled carbon nanotubes, polyethylene terephthalate, polymer fibers, metal fibers, and glass fibers.

[0015] Optionally, the catalytic material includes at least one of nano gold, nano silver, nano copper, nano platinum, and nano metal oxides; the conductive agent includes at least one of electro-carbon black, carbon microspheres, acetylene black, and Ketjen black.

[0016] Optionally, the thickness of the insulating layer is greater than or equal to the thickness of the active coating.

[0017] Optionally, the insulating layer includes an insulating material, a lithium salt, an adhesive, and conductive carbon;

[0018] wherein, the insulating material includes at least one of ceramic materials and inorganic solid electrolytes.

[0019] Optionally, the mass ratio of the insulating material in the insulating layer is greater than or equal to 80% and less than or equal to 95%;

[0020] The mass ratio of the lithium salt in the insulating layer is greater than or equal to 1% and less than or equal to 5%;

[0021] The mass ratio of the adhesive in the insulating layer is greater than or equal to 3% and less than or equal to 5%;

[0022] The mass ratio of the conductive carbon in the insulating layer is greater than or equal to 3% and less than or equal to 8%

[0023] In a second aspect, an embodiment of the present application further provides a battery, including:

[0024] A battery case, a positive electrode sheet, and a negative electrode sheet as described in the first aspect.

[0025] The above technical solution has the following advantages or beneficial effects:

[0026] The negative electrode sheet provided by the embodiment of the present application uses the setting of the active coating with a porous structure to release the stress generated during the charge and discharge process of the battery for forming lithium dendrites, so as to inhibit the growth of lithium dendrites on the negative electrode sheet, avoid the situation that lithium dendrites pierce the separator, and improve the safety of the battery. Description of the Drawings

[0027] Figure 1 is a schematic structural diagram of a negative electrode sheet provided by an embodiment of the present application;

[0028] Brief Description of the Drawings: 10, negative current collector; 20, active coating; 30, insulating layer. Detailed Embodiments

[0029] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0030] Please refer to Figure 1 , Figure 1 which is a schematic structural diagram of a negative electrode sheet provided by an embodiment of the present application. As Figure 1 shown, the negative electrode sheet includes:

[0031] a negative current collector 10, and an active coating 20 and an insulating layer 30 provided on at least one side of the negative current collector 10;

[0032] The negative current collector 10, the active coating 20, and the insulating layer 30 are sequentially stacked, and the active coating 20 is located between the negative current collector 10 and the insulating layer 30; the active coating 20 is a porous structure coating.

[0033] Exemplarily, the negative current collector 10 may be at least one of copper foil, carbon-coated copper foil, copper foam, and perforated copper foil. In applications, it is preferably set that the negative current collector 10 is copper foil or copper foam.

[0034] Among them, the active coating 20 includes a two-dimensional material and a network construction material, and the two-dimensional material and the network construction material form the porous structure;

[0035] Among them, the two-dimensional material includes at least one of two-dimensional carbides and nitrides, graphene, porous graphene, porous two-dimensional carbides and nitrides, two-dimensional sheet metal oxides, metal hydroxides, and metal sulfides.

[0036] The network construction material includes at least one of carbon nanotubes, multi-walled carbon nanotubes, polyethylene terephthalate, polymer fibers, metal fibers, and glass fibers.

[0037] It should be noted that when preparing the negative electrode active coating based on related technologies and the negative electrode active coating material used includes at least two different active materials, although the particle sizes of different active materials are inconsistent, the particle shapes are basically similar. Therefore, when different active materials are mixed, they will only stack on each other, which will cause certain voids in the formed negative electrode active coating. However, after multiple rolling treatments (to improve the structural stability of the negative electrode active coating), the porosity of the negative electrode active coating will decrease sharply, which makes the void size of the negative electrode active coating decrease sharply. When facing the stress for forming lithium dendrites, due to the too small voids, the stress cannot be fully released, and it will impact the structure of the negative electrode active coating through the voids, resulting in poor safety of the negative electrode sheet in the later stage of charge-discharge cycles.

[0038] In the example of the present application, the active coating 20 is formed by mixing two-dimensional materials and network construction materials. The relationship between the two-dimensional materials and the network construction materials is not a simple stacking relationship, but they can cooperate with each other to form a three-dimensional porous structure similar to a honeycomb or network shape. Among them, the two-dimensional materials can be approximately understood as sheet materials, and the network construction materials can be approximately understood as columnar materials. Using the columnar materials to connect and support the sheet materials can enable the prepared active coating 20 to maintain better structural stability (still maintain a high porosity after multiple rolling treatments) even when there are large voids. With the above setting of the three-dimensional porous structure, the voids existing inside the active coating 20 can maintain a large space to fully release the stress generated during the charge-discharge process of the battery for forming lithium dendrites. On the one hand, it inhibits the growth of lithium dendrites on the negative electrode sheet and avoids the situation of lithium dendrites piercing the separator. On the other hand, it avoids the stress from impacting the structure of the active coating 20, thereby achieving the purpose of improving the safety of the battery.

[0039] The active coating 20 and the insulating layer 30 form a composite coating on the negative electrode current collector 10, and this composite coating is located on at least one side of the negative electrode current collector 10 to adapt to the coating setting requirements in complex scenarios.

[0040] Exemplarily, when there is only one such composite coating, this composite coating can be arranged on the first side of the negative electrode current collector 10 or on the second side of the negative electrode current collector 10; when there are two such composite coatings, one composite coating is arranged on the first side of the negative electrode current collector 10, and the other composite coating is arranged on the second side of the negative electrode current collector 10, where the first side and the second side of the negative electrode current collector 10 are the opposite sides of the negative electrode current collector 10.

[0041] Further, the active coating 20 may further include a catalytic material, a conductive material, and a binder material. Among them, the catalytic material can be used to promote the deposition of lithium metal, inhibit the generation of stress for forming lithium dendrites, and improve the kinetic performance of the battery; the conductive material can be used to enhance the processing performance of the active coating 20, so as to facilitate the coating operation of the active material for forming the active coating 20; the binder material can be used to enhance the adhesion between the active coating 20 and the negative electrode current collector 10, and promote the mixing of various materials in the active coating 20, so that the active coating 20 has better structural stability.

[0042] Exemplarily, the catalytic material may be at least one of nano gold, nano silver, nano copper, nano platinum, and nano metal oxide. The conductive material may be at least one of conductive carbon black, carbon microspheres, acetylene black, and Ketjen black. The binder material may be at least one of polyvinyl alcohol, acrylonitrile, acrylic acid, styrene-butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride, polyvinylpyrrolidone, and polyimide.

[0043] Optionally, the mass ratio of the two-dimensional material in the active coating 20 is greater than or equal to 50% and less than or equal to 70%;

[0044] The mass ratio of the network building material in the active coating 20 is greater than or equal to 10% and less than or equal to 30%;

[0045] The mass ratio of the catalytic material in the active coating 20 is greater than or equal to 3% and less than or equal to 7%;

[0046] The mass ratio of the conductive agent (i.e., the aforementioned conductive material) in the active coating 20 is greater than or equal to 3% and less than or equal to 5%;

[0047] The mass ratio of the binder material in the active coating 20 is greater than or equal to 3% and less than or equal to 5%.

[0048] Specifically, in the active coating 20, the sum of the mass ratios of the two-dimensional material, the network building material, the catalytic material, the conductive material, and the binder material is 100%. In applications, the two-dimensional material, the network building material, the catalytic material, the conductive material, and the binder material can be adaptively adjusted within the above numerical ranges according to actual needs. The embodiments of the present application do not limit this.

[0049] As described above, by using the two-dimensional material as the main body and blending an appropriate amount of network building material to form the active coating 20, the prepared active coating 20 can have better structural stability. This enables the active coating 20 to still maintain a high porosity after multiple rolling treatments, so as to release the stress for forming lithium dendrites, achieving the purpose of inhibiting the growth of lithium dendrites on the negative electrode sheet.

[0050] Optionally, the thickness of the insulating layer 30 is greater than or equal to the thickness of the active coating 20.

[0051] As described above, by setting the thickness of the insulating layer 30 to be greater than or equal to the thickness of the active coating 20, when a small amount of lithium dendrites are formed on the active coating 20, it can be ensured that the insulating layer 30 can separate the formed small amount of lithium dendrites from the battery separator, so as to avoid the situation that the lithium dendrites pierce the separator. Among them, the thickness of the active coating 20 can be greater than or equal to 1 and less than or equal to 5 microns, and the thickness of the insulating layer 30 can be greater than or equal to 3 and less than or equal to 5 microns. In the application, the thickness of the insulating layer 30 and the thickness of the active coating 20 can be adaptively adjusted according to actual needs, and the embodiments of the present application do not limit this.

[0052] Optionally, the insulating layer 30 includes an insulating material, a lithium salt, an adhesive, and conductive carbon.

[0053] The insulating material includes at least one of ceramic materials (such as silicates, aluminosilicates, kaolin, metal nitrides, borides, etc.) and inorganic solid electrolytes (such as glass electrolytes, ceramic electrolytes, Perovskite type, NaSiCON type, LiSiCON type, LiPON type, LiPOLiSiO type, and GARNET type, sulfide amorphous electrolytes such as LiSSiS, LiSPS, LiSBS).

[0054] Among them, the insulating material can be used to protect the separator to prevent contact between lithium dendrites and the separator in the presence of lithium dendrites, and avoid the situation that lithium dendrites pierce the separator and cause safety problems.

[0055] As described above, by setting the lithium salt in the insulating layer 30, not only can the insulating layer 30 have a lithium supplement function (that is, supplement the lost lithium ions of the positive electrode through the lithium salt in the insulating layer 30 to improve the first Coulomb efficiency of the battery), but also the thickness of the battery can be reduced (compared with the structure of additionally setting a coating for supplementing lithium ions), and the effect of further improving the energy density of the battery can be achieved.

[0056] Exemplarily, the lithium salt includes at least one of lithium perchlorate, lithium chloride, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium bis(fluorosulfonyl)imide.

[0057] Furthermore, the mass ratio of the insulating material in the insulating layer 30 is greater than or equal to 80% and less than or equal to 95%;

[0058] The mass ratio of the lithium salt in the insulating layer 30 is greater than or equal to 1% and less than or equal to 5%;

[0059] The mass ratio of the adhesive in the insulating layer 30 is greater than or equal to 3% and less than or equal to 5%.

[0060] The mass ratio of the conductive carbon in the insulating layer 30 is greater than or equal to 3% and less than or equal to 8%.

[0061] As described above, the mass ratio of the insulating material in the insulating layer 30 is limited within the range of 80% - 95% to ensure the stable performance of the insulating effect of the insulating layer 30. In applications, the mass ratios of the insulating material, lithium salt, adhesive, and conductive carbon in the insulating layer 30 can be adaptively adjusted within the above numerical range according to actual requirements, and the embodiments of the present application do not limit this.

[0062] The embodiments of the present application further provide a battery, which includes a battery case, a positive electrode sheet, and the negative electrode sheet provided in the foregoing embodiments.

[0063] Among them, the positive electrode active material on the positive electrode sheet can be at least one of metal oxides (such as lithium cobaltate, lithium nickelate, lithium manganate, nickel cobalt manganese ternary material, lithium nickel cobalt aluminate, lithium-rich manganese-based, lithium nickel manganate, iron tetroxide, lithium vanadate), polyanion salts (such as lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium oxygen vanadium phosphate, lithium cobalt phosphate, lithium nickel phosphate, lithium iron silicate, lithium iron fluorosulfate, lithium iron borate, lithium iron titanate), and other compounds (such as fluorides, sulfides, selenides). In applications, at least one of the above materials can be adaptively selected as the positive electrode active material according to requirements, and the embodiments of the present application do not limit this.

[0064] For easy understanding, examples are illustrated as follows:

[0065] It is assumed that the negative electrode current collector 10 is a copper foil with a thickness of 6 microns, the positive electrode current collector is an aluminum foil with a thickness of 10 microns, the positive electrode active material is lithium cobaltate, the positive electrode conductive agent is conductive carbon black, and the positive electrode binder is polyvinylidene fluoride.

[0066] It is further assumed that the preparation method of reduced graphene oxide (rGO) is:

[0067] Graphene oxide (prepared from flake graphite) is uniformly dispersed in ethylene glycol. After being sufficiently stirred by a stirring device for 30 minutes, the stirred slurry is transferred to a round-bottom flask and refluxed at 130 degrees Celsius for 3 hours. Finally, it is cooled to room temperature, and the reduced graphene oxide is collected from the cooled solution by a centrifugation device.

[0068] Two-dimensional titanium carbide (Ti3C2T x )'s preparation method is:

[0069] Two-dimensional titanium carbide was synthesized by acid etching Ti3AlC2 with a mixture of hydrochloric acid (HCl) and lithium fluoride (LiF). The specific process is as follows: LiF was added to 9M HCl (in a polytetrafluoroethylene beaker) within ten minutes, and then Ti3AlC2 was slowly added to the above mixed solution within 10 minutes. Subsequently, it was etched in a water bath at 35 °C for 24 hours. Then the acidic suspension was washed and centrifuged until the pH of the supernatant reached 7. Then it was vacuum dried at 80 °C for half a day to obtain two-dimensional titanium carbide powder.

[0070] The preparation method of the positive electrode sheet is as follows:

[0071] By weight fraction, 96% of the positive electrode active material (lithium cobaltate), 2% of the positive electrode conductive agent (conductive carbon black SP), and 2% of the positive electrode binder (polyvinylidene fluoride) were added to N-methylpyrrolidone to prepare a positive electrode lithium cobaltate slurry, and the positive electrode lithium cobaltate slurry was coated on the positive electrode current collector (both sides of the aluminum foil). After drying, rolling, slitting, and welding the positive electrode tab, the positive electrode sheet was prepared.

[0072] The electrolyte is composed of a lithium salt and a solvent. The organic solvent is a mixture of propylene carbonate, ethylene carbonate, and dimethyl carbonate, and the volume ratio of the three solvents is 1:1:1. The lithium salt is LiPF6, and the corresponding concentration is 1M.

[0073] The preparation method of the battery is as follows:

[0074] The battery was assembled in a glove box filled with argon, and the moisture and oxygen content were both kept below 1.0 ppm. The cut positive electrode, negative electrode, separator, and electrolyte were assembled in the following order: positive electrode case, positive electrode sheet, electrolyte (appropriately infiltrated), separator, electrolyte (appropriately infiltrated), negative electrode sheet, electrolyte (appropriately infiltrated), gasket, spring piece, negative electrode case. Then it was sealed with a sealing machine and left at room temperature for 12 h.

[0075] Control Group 1:

[0076] The negative electrode sheet uses a lithium sheet, and the electrolyte, separator, and positive electrode sheet are prepared according to the above preparation method, and the battery corresponding to Control Group 1 is obtained through the above battery assembly method.

[0077] Experimental Group 1:

[0078] The negative electrode active paste (by mass fraction: take 70 parts of reduced graphene oxide, 20 parts of carbon nanotubes, 5 parts of silver nanoparticles, 2 parts of conductive carbon, and 3 parts of polyvinylidene fluoride dissolved in N-methylpyrrolidone solution to form the negative electrode active paste) is coated on the negative electrode current collector 10 (copper foil) to form the active coating 20; the insulating paste (by mass fraction: take 90 parts of garnet-type solid electrolyte, 7 parts of conductive carbon, and 3 parts of polyvinylidene fluoride dissolved in N-methylpyrrolidone solution to form the protective layer paste) is coated on the active coating 20 to form the insulating layer 30, that is, the negative electrode sheet is formed. The electrolyte, separator, and positive electrode sheet are prepared according to the above preparation method, and the battery corresponding to Experimental Group 1 is obtained through the above battery assembly method.

[0079] Experimental Group 2:

[0080] The difference from Experimental Group 1 is that the reduced graphene oxide in the negative electrode active paste is replaced by two-dimensional titanium carbide.

[0081] Experimental Group 3:

[0082] The difference from Experimental Group 1 is that the mass fraction of silver nanoparticles in the negative electrode active paste is adjusted from 5 parts to 3 parts, and the mass fraction of conductive carbon is adjusted from 2 parts to 4 parts.

[0083] Experimental Group 4:

[0084] The difference from Experimental Group 3 is that 7 parts of conductive carbon in the insulating paste are replaced by 1 part of lithium hexafluorophosphate and 6 parts of conductive carbon.

[0085] Experimental Group 5:

[0086] The difference from Experimental Group 3 is that 7 parts of conductive carbon in the insulating paste are replaced by 3 parts of lithium hexafluorophosphate and 4 parts of conductive carbon.

[0087] Experimental Group 6:

[0088] The difference from Experimental Group 3 is that 7 parts of conductive carbon in the insulating paste are replaced by 5 parts of lithium hexafluorophosphate and 2 parts of conductive carbon.

[0089] Experimental Group 7:

[0090] The difference from Experimental Group 5 is that 70 parts of reduced graphene oxide in the negative electrode active paste are replaced by 35 parts of reduced graphene oxide and 35 parts of two-dimensional titanium carbide.

[0091] The composition ratios of the negative electrode sheet materials of Experimental Groups 1 to 7 and Control Group 1 are shown in Table 1:

[0092]

[0093]

[0094] Table 1

[0095] The battery performances of Experimental Groups 1 to 7 and Control Group 1 are shown in Table 2 as follows:

[0096]

[0097]

[0098] Table 2

[0099] As can be seen from Table 1 and Table 2, the setting of the active coating 20 with a porous structure on the negative electrode can improve the initial Coulomb efficiency of the battery and the charge-discharge Coulomb efficiency, while the lithium salt in the insulating layer 30 can effectively improve the retention rate of the battery cycle capacity.

[0100] The embodiments of the present application have been described above in conjunction with the accompanying drawings. However, the present application is not limited to the above specific embodiments. The above specific embodiments are merely illustrative rather than restrictive. Under the inspiration of the present application, those of ordinary skill in the art can also make many forms without departing from the spirit of the present application and the scope protected by the claims, and all of them belong to the protection scope of the present application.

Claims

1. A negative electrode sheet, characterized in that, Comprising: a negative current collector, and an active coating and an insulating layer provided on at least one side of the negative current collector; the negative current collector, the active coating, and the insulating layer are sequentially stacked, and the active coating is located between the negative current collector and the insulating layer; the active coating is a porous structure coating; the active coating includes a two-dimensional material, a network construction material, a catalytic material, and a conductive agent, and the two-dimensional material and the network construction material form the porous structure; the mass ratio of the two-dimensional material in the active coating is greater than or equal to 50% and less than or equal to 70%; the mass ratio of the network construction material in the active coating is greater than or equal to 10% and less than or equal to 30%; the mass ratio of the catalytic material in the active coating is greater than or equal to 3% and less than or equal to 7%; the two-dimensional material includes at least one of two-dimensional titanium carbide and reduced graphene oxide, the network construction material includes carbon nanotubes, the catalytic material includes silver nanoparticles, and the conductive agent includes conductive carbon.

2. The negative electrode sheet according to claim 1, wherein the thickness of the insulating layer is greater than or equal to the thickness of the active coating.

3. The negative electrode sheet according to claim 1, wherein, the insulating layer includes an insulating material, a lithium salt, an adhesive, and conductive carbon; wherein, the insulating material includes at least one of a ceramic material and an inorganic solid electrolyte.

4. The negative electrode sheet according to claim 3, wherein the mass ratio of the insulating material in the insulating layer is greater than or equal to 80% and less than or equal to 95%.

5. A battery, characterized in that, Comprising a battery case, a positive electrode sheet, and the negative electrode sheet according to any one of claims 1-4.

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