CN108736014A - Composite negative pole and preparation method thereof includes the alkali metal battery of composite negative pole - Google Patents

Abstract

The invention discloses a composite negative pole, a preparation method thereof, and an alkali metal battery comprising the composite negative pole. According to an exemplary embodiment, a composite negative electrode for an alkali metal battery may include: a current collector; and a composite negative active layer formed on the current collector, the composite negative active layer including at least two different negative electrodes active material and have a porosity of 20% to 90%. The composite negative electrode of the present invention can reduce or prevent the phenomenon of alkali metal precipitation and dendrite growth on the surface, thereby effectively improving the safety, energy density and working performance of the alkali metal battery under high current density.

Description

Composite negative electrode and preparation method thereof, alkali metal battery including composite negative electrode

technical field

The present invention generally relates to the fields of electrochemical energy storage devices and new energy sources, and more particularly relates to a composite negative electrode for an alkali metal (lithium, sodium, potassium) battery, a preparation method thereof, and an alkali metal comprising the composite negative electrode Battery.

Background technique

The negative electrode active materials used in the current commercialization of lithium-ion batteries and the alkali metal batteries under development mainly include various carbon materials (such as artificial graphite, natural graphite, artificial mesocarbon microspheres, soft carbon, hard carbon, etc.) etc.) and silicon-containing negative electrodes (such as silicon oxide, silicon-carbon composite negative electrodes, etc.) materials, etc. Compared with carbon materials, silicon-based anode materials have higher theoretical specific capacity (4200mAh/g) and relatively low electrode potential (vs Li/Li+), so they have great application potential. However, silicon-based anode materials also have some defects, such as large volume expansion during charge and discharge, and the first-week Coulombic efficiency is not high. In order to increase the energy density of the battery, researchers are trying to use silicon-carbon composite materials as the negative electrode active material of the battery. Compared with the negative electrode active materials such as pure silicon negative electrode and silicon oxide, the Coulombic efficiency and volume expansion have achieved significant improvement in the first week. improve. The use of such composite anode active materials has improved the energy density of existing lithium-ion batteries to a certain extent, but there is still a need to further increase the energy density of batteries while taking into account the cycle characteristics of working conditions and prolong service life.

In order to further increase the energy density of batteries, metal lithium and lithium alloy anodes are one of the future development directions. Lithium metal has a high theoretical specific capacity (3860mAh/g) and a very low standard electrode potential (-3.04V), which has great application potential. However, there are significant defects in pure metal lithium anodes and lithium alloy anodes, mainly because lithium batteries using metal lithium anodes have serious lithium pulverization and lithium dendrite growth during charging and discharging, while batteries using lithium alloy anodes are also There are problems such as pulverization and lithium segregation and aggregation, which are more prominent at high rate/high current density. Since lithium ions are mainly deposited and extracted on a limited surface on the negative electrode side, the performance of withstanding high current (larger current per unit area) is poor, so to realize the practical application of batteries using pure metal lithium and lithium alloy negative electrodes, Many problems still need to be overcome.

Contents of the invention

One aspect of the present invention is to provide a high-porosity composite negative electrode for alkali metal (lithium, sodium, potassium) batteries and a preparation method thereof, which can reduce or prevent surface alkali metal precipitation and dendrite growth, thereby effectively Improve the safety, energy density and performance of alkali metal batteries at high current densities.

Another aspect of the present invention is to provide an alkali metal battery including the above composite negative electrode.

According to an exemplary embodiment, a composite negative electrode for an alkali metal battery may include: a current collector; and a composite negative active layer formed on the current collector, the composite negative active layer including at least two different negative electrodes active material and have a porosity of 20% to 90%.

In some examples, the composite negative active layer has a porosity of 25% to 60%.

In some examples, the composite negative active layer has a porosity of 30% to 50%.

In some examples, the mass of each of the at least two different negative electrode active materials accounts for 1% to 99% of the total effective electrode mass of the composite negative electrode active layer.

In some examples, the at least two different negative electrode active materials are selected from the group consisting of lithium metal, lithium alloy, sodium metal, sodium alloy, potassium metal, potassium alloy, natural graphite, artificial graphite, artificial mesophase Carbon microspheres, hard carbon, soft carbon, lithium titanate, silicon oxide, silicon, silicon-carbon composite anode materials, tin-containing anode materials, transition metal compound anode materials A _x B _y , where A is Ti, V, Cr , Fe, Co, Ni, Mn, Cu, Zn, Ru or Mo, B is F, O, S or N, x and y are positive integers.

In some examples, the at least two different negative electrode active materials are selected from lithium titanate, soft carbon, and hard carbon.

In some examples, the composite negative electrode further includes: an interface layer disposed between the current collector and the composite negative electrode active layer to improve electrical conductivity between the two.

In some examples, the interface layer includes graphene.

According to another exemplary embodiment, a method of preparing a composite negative electrode for an alkali metal battery may include: providing a current collector; and forming a composite negative active layer on the current collector, the composite negative active layer comprising at least two different negative active materials and have a porosity of 20% to 90%.

In some examples, forming a composite negative electrode active layer on the current collector includes: forming a slurry of at least two different negative electrode active materials; and spraying, extrusion coating, spin coating, rolling, or sputtering The slurry is applied to the current collector.

According to another exemplary embodiment, an alkali metal battery may include: a positive electrode including a positive electrode current collector and a positive electrode active layer disposed on the positive electrode current collector; the composite negative electrode described above; and a separator disposed on the positive electrode and the composite negative electrode, and the positive electrode current collector and the negative electrode current collector are located outside.

The composite electrode provided by the embodiment of the present invention and the alkali metal battery comprising the composite electrode have better safety and higher energy density and energy efficiency than traditional alkali metal (lithium, sodium, potassium) batteries. The composite electrode can be used to assemble traditional alkali metal (lithium, sodium, potassium) ion batteries such as lithium ion batteries, and can also assemble alkali metal batteries that use alkali metals (lithium, sodium, potassium) as negative electrodes indirectly or directly. The batteries assembled using the composite electrodes are significantly different from the alkali metal (lithium, sodium, potassium) batteries using pure metals (lithium, sodium, potassium) and their alloys as negative electrodes. Traditionally, pure metals (lithium, sodium, potassium) When charging and discharging a negative electrode battery, the alkali metal (lithium, sodium, potassium) ions are mainly deposited and extracted on the surface of the negative electrode, and the alkali metal (lithium, sodium, potassium) battery alkali metal ions assembled using the composite electrode can be Intercalation, deposition, and deintercalation are carried out inside the electrode material particles and in the gaps between the electrode material particles, so that there will be no surface metal precipitation and dendrite growth, thus effectively improving the safety of alkali metal (lithium, sodium, potassium) batteries. Energy density and performance at high current densities.

The above and other features and advantages of the present invention will become apparent from the following description of the exemplary embodiments.

Description of drawings

FIG. 1 shows an electrode structure of an alkali metal battery according to an embodiment of the present invention.

FIG. 2 shows a composite negative electrode according to another embodiment of the present invention.

Fig. 3 shows a flowchart of a method for preparing a composite negative electrode according to an embodiment of the present invention.

FIG. 4A shows a surface topography SEM image of a composite negative electrode according to an embodiment of the present invention.

Fig. 4B shows a cross-sectional SEM image of a composite negative electrode according to an embodiment of the present invention.

FIG. 5 shows charge and discharge curves of an alkali metal battery including a composite negative electrode according to an embodiment of the present invention.

FIG. 6 shows the variation curves of capacity and coulombic efficiency during cycling of an alkali metal battery including a conventional negative electrode.

FIG. 7 shows the capacity variation curves of an alkali metal battery including a conventional negative electrode and an alkali metal battery including a composite negative electrode according to an embodiment of the present invention during cycling.

Fig. 8 shows the coulombic efficiency variation curves of an alkali metal battery including a conventional negative electrode and an alkali metal battery including a composite negative electrode according to an embodiment of the present invention during cycling.

Detailed ways

Exemplary embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an electrode structure of an alkali metal battery 100 according to an embodiment of the present invention. As shown in FIG. 1 , an alkali metal battery 100 may include a negative electrode 110, a positive electrode 120, and a separator 130 therebetween. The negative electrode 110 may include a negative electrode current collector 112 and a composite negative electrode active layer 114 formed on the negative electrode current collector 112 , and thus is also referred to as a composite negative electrode 110 . The positive electrode 120 may also include a positive electrode collector 122 and a positive electrode active layer 124 formed on the positive electrode collector 122 .

Each of the negative electrode collector 112 and the positive electrode collector 122 may include a metal material with good electrical conductivity, such as but not limited to copper, copper alloy containing more than 80% copper, stainless steel, titanium, titanium alloy, nickel, nickel alloy, iron, ferroalloy etc. Copper and copper alloys are preferred in view of electrical conductivity and cost. Each of the negative electrode collector 112 and the positive electrode collector 122 may be in the form of a metal foil, such as a dense foil or a porous foil, and its thickness may be, for example, 1 μm˜20 mm, preferably 2˜8 μm.

Composite negative electrode active layer 114 can comprise the mixture of two or more different negative electrode active materials, and these negative electrode active materials can be selected from commonly used in lithium battery, lithium ion battery, sodium battery, sodium ion battery, potassium battery, potassium ion battery negative electrode active materials, examples of which include, but are not limited to, lithium metal, lithium alloy, sodium metal, sodium alloy, potassium metal, potassium alloy, natural graphite, artificial graphite, artificial mesocarbon microspheres, hard carbon, soft carbon, titanic acid Lithium, silicon oxide, silicon, silicon-carbon composite negative electrode materials, tin-containing negative electrode materials, and transition metal compound negative electrode materials (the general expression of which is A _x By _y , where A is a transition metal element with variable valence, including but not limited to Ti, V, Cr, Fe, Co, Ni, Mn, Cu, Zn, Ru, Mo; B is a non-metallic element, including but not limited to F, O, S, N; x and y are positive integers), where the transition metal Examples of compound negative electrode materials include, but are not limited to, eg, titanium dioxide, manganese dioxide, and the like. In some preferred embodiments, the composite negative electrode active layer 114 may include lithium titanate, soft carbon, hard carbon and other electrode materials with fast kinetic response.

As mentioned above, the composite negative electrode active layer 114 may include a mixture of two or more different negative electrode active materials. Wherein, the mass fraction of each material may be in the range of 1% to 99%, and the specific value may vary depending on the material. The sum of the parts by mass of each material may be 1.

Conventional anode active layers generally have a dense and compact structure to provide a large amount of anode active materials in a limited space. Different from the conventional technology, the composite negative electrode active layer 114 of the present invention has a porous structure, and its porosity is above 20%, such as between 20% and 90%, or between 20% and 85%, preferably between Between 25% and 60%, more preferably between 30% and 50%. By adopting the above-mentioned composite material, it can contribute to the formation of a high-porosity negative electrode active layer.

The diaphragm 130 may include, for example, a polymer film. Examples of polymeric materials used to form the diaphragm 130 include, but are not limited to, polypropylene, polyethylene, ethylene oxide, polypropylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethylmethacrylate ester, polyacrylonitrile, polyimide, polyetherimide, polycarbonate, polyaramid, cellulose, and any combination thereof. In some embodiments, the thickness of the membrane 130 may be in the range of 6-60 μm, preferably in the range of 6-25 μm. In some embodiments, the separator 130 may be porous to facilitate the circulation of the electrolyte, for example, the separator 130 may have a porosity of 30%-90%.

The positive electrode active layer 124 may include various commonly used positive electrode active materials, examples of which include but are not limited to lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium-rich layered oxide, nickel manganese acid Lithium, lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate, lithium nickel phosphate, lithium iron manganese phosphate, iron phosphate, manganese phosphate, cobalt phosphate, nickel phosphate, lithium iron silicate, lithium manganese silicate, lithium cobalt silicate, Lithium nickel silicate, iron silicate, manganese silicate, cobalt silicate, nickel silicate, manganese dioxide, iron sulfide, manganese sulfide, cobalt sulfide, nickel sulfide, titanium sulfide, iron sulfate, sulfur carbon and vanadium oxide, and any combination of them.

The electrode structure of the alkali metal battery 100 is briefly described above. It should be understood that the above-mentioned negative electrode 110, positive electrode 120, and separator 130 can be stacked on each other or wound into a predetermined shape, and then packaged in a battery case, and the positive electrode current collector 124 and the negative electrode current collector 114 can be connected to connection terminals outside the case, Or connect to the case itself which acts as a connection terminal. The battery 100 may be a solid battery or a liquid battery. In this case, an electrolyte is injected into the battery case, and the electrolyte may be an aqueous electrolyte or an organic electrolyte without water.

The inventors of the present invention have found that when a composite negative electrode active layer with a porosity of more than 20% is used, compared with the prior art, the precipitation of metal lithium and the growth of dendrites can be reduced. Although not limited to this in theory, the inventors believe that this may be related to the porous structure of the composite negative electrode active layer. When traditional alkaline batteries are charged and discharged, alkali metal (lithium, sodium, potassium) ions are mainly deposited and extracted on the surface of the negative electrode, and when the composite negative electrode with high porosity of the present invention is used, the alkali metal ions can be deposited on the negative electrode material. Intercalation, deposition, and deintercalation are carried out in the interior of the particles and in the interstices of the particles, so there will be no surface metal precipitation and dendrite growth, thereby effectively improving the safety, energy density, and performance of the alkali metal battery at high current densities. . Experiments have found that when the porosity of the composite negative electrode active layer 114 is between 25% and 60%, more preferably between 30% and 50%, the phenomenon of metal lithium precipitation and dendrite growth can be significantly reduced, greatly improving safety , while maintaining a large energy density.

Although not shown, in some embodiments, the negative electrode 110 may also be pre-lithiated to further improve its cycle characteristics.

FIG. 2 shows a composite negative electrode according to another embodiment of the present invention. In FIG. 2, the same components as those in FIG. 1 are denoted by the same reference numerals, and repeated description thereof will be omitted here.

Referring to FIG. 2 , the negative electrode 110 may further include an interface layer 116 formed between the negative electrode collector 112 and the composite negative active layer 114 to enhance the interfacial conductivity between the negative current collector 112 and the composite negative active layer 114. The interface layer 116 may include a material with excellent electrical conductivity, such as graphene, which can be easily grown on, for example, a Cu current collector, and may be grown in a two-dimensional layered shape, or in a three-dimensional upright shape. By setting the graphene interface layer 116, the internal resistance of the alkali metal battery can be significantly reduced, thereby further improving its cycle performance. In some embodiments, graphene material can also be mixed in the composite negative electrode active layer 114 to improve current conduction properties, although graphene does not provide activity.

FIG. 3 shows a flowchart of a method 200 for preparing a composite negative electrode according to an embodiment of the present invention. As shown in FIG. 3, the method 200 may include step S210, providing a negative electrode current collector, such as the negative electrode current collector 112 described above, which may be a commercially purchased metal foil, or further processed, such as forming a plurality of through-holes by stamping. holes, or are punched into a predetermined shape suitable for fitting into a battery such as a button cell. It should be understood that after forming a plurality of negative electrodes on the metal foil, it can be punched into multiple individual negative electrode sheets.

Continuing to refer to FIG. 3 , in step S220 , a high-porosity composite negative active layer is formed on the negative current collector. The step of forming the negative electrode active layer may include forming a mixed slurry of two or more different electrode materials, and the slurry may include an electrode coating binder, such as an organic binder. The slurry is then applied to a current collector and dried to form a negative electrode. In the slurry, the proportion of each electrode material to the total mass of the effective electrode can range from 1% to 99%, and the specific value can vary depending on the material. The method of applying the slurry includes, but is not limited to, extrusion coating, spray coating, rolling, sputtering, and spin coating, among which spray coating, extrusion coating, and rolling are preferred.

Although not shown, in some embodiments, a step of forming an interface layer such as a graphene layer on the current collector is further included between steps S210 and S220. It can be understood that the graphene layer can be directly grown on the current collector by methods such as molecular beam epitaxy (MBE) or chemical vapor deposition (CVD), or can be first grown on other substrates and then transferred to the current collector. The growth and transfer techniques of graphene layers have been widely reported in various literatures and will not be repeated here.

After the negative electrode is formed, the negative electrode, separator and positive electrode can be assembled into a battery core as in the prior art, and then the battery core is packaged in a battery case to form an alkali metal battery, and these steps will not be described in detail here .

Fig. 4A shows a surface topography SEM image of a composite negative electrode according to an embodiment of the present invention, and Fig. 4B shows a cross-sectional topography SEM image thereof. The composite negative electrode includes a graphene interface layer formed on a current collector and a composite negative electrode active layer, wherein the composite negative electrode active layer includes a mixture of lithium titanate and soft carbon. As shown in Figures 4A and 4B, the composite negative active layer exhibits a structure with high porosity.

A half-cell was assembled using the negative electrode shown in FIGS. 4A and 4B and metal lithium, and then its charge and discharge characteristics were measured. The results are shown in the graph of FIG. 5 . From the charge-discharge curve shown in Figure 5, it can be seen that the high-porosity composite negative electrode of the present invention has a higher first-cycle Coulombic efficiency, and has a higher capacity under a low potential platform, so the composite negative electrode is used to match the positive electrode When forming an alkali metal battery, the Coulombic efficiency and discharge potential of the full battery can be improved.

FIG. 6 shows the variation curves of capacity and coulombic efficiency during cycling of an alkali metal battery including a conventional negative electrode. FIG. 7 shows the capacity variation curves of an alkali metal battery including a conventional negative electrode and an alkali metal battery including a composite negative electrode according to an embodiment of the present invention during cycling. Fig. 8 shows the coulombic efficiency variation curves of an alkali metal battery including a conventional negative electrode and an alkali metal battery including a composite negative electrode according to an embodiment of the present invention during cycling. The conventional alkali metal battery shown in Fig. 6-8 comprises lithium cobaltate positive electrode material and carbon negative electrode material, and the alkali metal battery according to an embodiment of the present invention shown in Fig. 7 and Fig. 8 also comprises lithium cobaltate positive electrode material, but its The negative electrode includes a high-porosity composite layer of lithium titanate and soft carbon. Referring to FIG. 6, it can be seen that the capacity of the conventional alkali metal battery decreases significantly as the number of cycles increases. In contrast, as shown in FIG. 7 , the capacity of the alkali metal battery of the present invention remains basically unchanged as the number of cycles increases, and is much larger than that of conventional batteries. In addition, it can be seen from FIG. 8 that the coulombic efficiency of the battery of the present invention is also higher than that of the conventional battery. Therefore, while improving the safety, the present invention also achieves a significant improvement in the cycle characteristics of the alkali metal battery.

Some examples of the composite negative electrode of the present invention are described below. In these examples, the composite negative electrode active layer is composed of negative electrode material 1, negative electrode material 2, and negative electrode material 3, wherein at least two of negative electrode material 1, negative electrode material 2, and negative electrode material 3 are different from each other, and can be selected from the following materials: 1, metallic lithium; 2, lithium alloy; 3, artificial graphite; 4, natural graphite; 5, artificial mesocarbon microspheres; 6, hard carbon; 7, soft carbon; 8, lithium titanate; 9, silicon oxide ; 10, silicon; 11, silicon-carbon composite material; 12, negative electrode containing tin; 13, transition metal compound A _x By _y , wherein A is a transition metal element with variable valence, including but not limited to Ti, V, Cr, Fe, Co, Ni, Mn, Cu, Zn, Ru, Mo, B are non-metallic elements, including but not limited to F, O, S, N, x and y are positive integers, examples of which are titanium dioxide, manganese dioxide, etc.; 14, Other suitable negative electrode materials for lithium batteries, lithium-ion batteries, sodium batteries, sodium-ion batteries, potassium batteries, and potassium-ion batteries. The mass proportion of each of the negative electrode material 1 , the negative electrode material 2 and the negative electrode material 3 may be in the range of 1% to 99%, and the sum of the mass proportions of the three materials is 1.

The negative current collector can be selected from the following materials: 1, copper; 2, copper alloy containing copper mass fraction higher than 80%; 3, nickel; 4, nickel alloy; 5, titanium; 6, titanium alloy; 7, iron; 8 , iron alloy; 9, other suitable negative electrode current collector materials.

The composite negative electrode preparation process may include: 1. Roll pressing; 2. Extrusion coating; 3. Spray coating; 4. Spin coating; 5. Other suitable methods for composite negative electrode preparation.

Electrode coating binder can include: 1, polyvinylidene fluoride; 2, carboxymethyl cellulose; 3, polymethyl acrylate; 4, polyamideimide; 5, polyimide; 6, polycyclic Ethylene oxide; 7, polypropylene oxide; 8, styrene-butadiene rubber; 9, polyacrylonitrile; 10, cyclodextrin; 11, pectin; Adhesive-coated materials.

The prepared composite negative electrode may have a porosity in the range of 20% to 90%, preferably in the range of 30% to 50%.

Table 1 below lists Examples 1-45. Experiments have shown that these examples can significantly inhibit the precipitation of lithium metal and dendrite growth, greatly improving safety while maintaining a large energy density.

Table 1

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the scope of the present invention. Protection scope, within the spirit and principles of the present invention, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.

Claims (11)

1. a kind of composite negative pole for alkali metal battery, including：

Collector；And

The composite negative pole active layer being formed on the collector, the composite negative pole active layer include at least two different negative Pole active material, and with 20% to 90% porosity.

2. composite negative pole as described in claim 1, wherein the composite negative pole active layer has 25% to 60% hole Rate.

3. composite negative pole as claimed in claim 2, wherein the composite negative pole active layer has 30% to 50% hole Rate.

4. composite negative pole as described in claim 1, wherein in described at least two different negative electrode active materials each Quality accounts for the 1% to 99% of the active electrode gross mass of the composite negative pole active layer.

5. composite negative pole as described in claim 1, wherein it includes such as that described at least two different negative electrode active materials, which are selected from, The group of lower material：Lithium metal, lithium alloy, metallic sodium, sodium alloy, metallic potassium, potassium-sodium alloy, natural graphite, artificial graphite, it is artificial in Between phase carbosphere, hard carbon, soft carbon, lithium titanate, the sub- silicon of oxidation, silicon, silicon-carbon cathode composite materials, containing tin negative pole material, transition Metallic compound negative material A_xB_y, wherein A be Ti, V, Cr, Fe, Co, Ni, Mn, Cu, Zn, Ru or Mo, B F, O, S or N, x with Y is positive integer.

6. composite negative pole as described in claim 1, wherein described at least two different negative electrode active materials are selected from metatitanic acid Lithium, soft carbon and hard carbon.

7. composite negative pole as described in claim 1, further includes：

Boundary layer is arranged between the collector and the composite negative pole active layer to improve electric conductivity between the two.

8. composite negative pole as claimed in claim 7, wherein the boundary layer includes graphene.

9. a kind of method preparing the composite negative pole for alkali metal battery, including：

Collector is provided；And

Composite negative pole active layer is formed on the collector, the composite negative pole active layer includes at least two different cathode Active material, and with 20% to 90% porosity.

10. method as claimed in claim 9, wherein forming composite negative pole active layer on the collector includes：

Form the slurry of at least two different negative electrode active materials；And

The slurry is applied on the collector by spraying, extrusion coated, spin coating, roll-in or sputtering.

11. a kind of alkali metal battery, including：

Anode, including plus plate current-collecting body and the positive-active layer that is arranged on the plus plate current-collecting body；

Composite negative pole described in any one of claim 1 to 8；And

Diaphragm, setting is between the anode and the composite negative pole, and the plus plate current-collecting body and the negative current collector Positioned at outside.