CN117199385A - Composite current collector, preparation method thereof, electrode plate and secondary battery - Google Patents
Composite current collector, preparation method thereof, electrode plate and secondary battery Download PDFInfo
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- CN117199385A CN117199385A CN202311134878.XA CN202311134878A CN117199385A CN 117199385 A CN117199385 A CN 117199385A CN 202311134878 A CN202311134878 A CN 202311134878A CN 117199385 A CN117199385 A CN 117199385A
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Landscapes
- Cell Electrode Carriers And Collectors (AREA)
Abstract
The invention provides a composite current collector and a preparation method thereof, an electrode plate and a secondary battery, wherein the composite current collector comprises an energy base layer and a conductive metal layer deposited on at least one surface of the energy base layer; the energy base layer comprises a base layer and an energy body which is at least partially embedded in the base layer and stores energy; the energy body is used for releasing stored energy when the triggering temperature is 85-130 ℃ so as to eject the conductive metal deposited on the surface of the energy body out of the conductive metal layer, and the melting point of the matrix layer is larger than the triggering temperature. Compared with the prior art, the composite current collector provided by the invention can break the conductive metal layer into mutually independent small blocks before thermal runaway, so that short-circuit current is blocked, heat accumulation is cut off from the source, thermal runaway of a battery core is avoided, and the thermal runaway problem caused by poor thermal conductivity of the conventional composite current collector is solved.
Description
Technical Field
The invention relates to the field of secondary batteries, in particular to a composite current collector, a preparation method thereof, an electrode plate and a secondary battery.
Background
The lithium ion battery has the advantages of high energy density, no memory effect, long cycle life, environmental friendliness and the like, and is widely applied to products such as 3C, electric automobiles, electric tools and the like. As the lithium battery industry is more and more competitive, so is the demand for energy density of lithium batteries, one way of which is to meet this demand by using a composite current collector.
The common composite current collector is a typical sandwich structure and comprises a high polymer material layer and a conductive metal layer deposited on the surface of the high polymer material layer by means of evaporation and the like. For example, a composite aluminum foil current collector with a thickness of 8 μm, which includes a1 μm thick aluminized layer + a 6 μm thick polymer material layer + a1 μm thick aluminized layer. Compared with the conventional aluminum foil current collector, the composite current collector can reduce the weight of the current collector on one hand, so that the mass energy density of the battery core is improved; on the other hand, the generation of section burrs during pole piece fracture can be reduced, so that the probability of short circuit of the battery cell is reduced, and the mechanical safety performance of the battery cell is improved. For example, the total mass of an 8 μm thick composite aluminum foil current collector is reduced by about 40% and the cell mass is reduced by about 1.2% (aluminum foil current collector mass is 3wt% of cell mass) compared to an 8 μm thick conventional aluminum foil current collector, and the mass energy density of the cell is improved by 1.2%.
However, the existing composite current collector also has the following problems: because the conductive metal layers with better thermal conductivity at both sides of the composite current collector are very thin (generally 1-2 μm), but the high polymer material layer (the thickness of which is generally more than 2 times of the thickness of the conductive metal layer) which occupies the main part of the composite current collector has poor thermal conductivity, the accumulation of heat is extremely easy to cause, when the accumulation of heat reaches a certain degree, SEI film, electrolyte, cathode active substances and the like are decomposed successively, and finally thermal runaway reaction occurs, and the battery core fires or even explodes.
In view of the foregoing, it is necessary to provide a solution to the above-mentioned problems.
Disclosure of Invention
One of the objects of the present invention is: in order to overcome the defects in the prior art, the composite current collector is provided to solve the problem of thermal runaway caused by poor thermal conductivity of the conventional composite current collector.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a composite current collector comprising:
an energy base layer comprising a base layer and an energy body at least partially embedded in the base layer and storing energy;
a conductive metal layer deposited on at least one surface of the energy base layer;
the energy body is used for releasing stored energy when the triggering temperature is 85-130 ℃ so as to eject the conductive metal deposited on the surface of the energy body out of the conductive metal layer, and the melting point of the matrix layer is larger than the triggering temperature.
Preferably, the ratio of the thickness of the base layer to the thickness of the conductive metal layer is (2-50): 1; the matrix layer is one or more of Polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), poly-p-phenylene terephthalamide (PPA) and Polyimide (PI).
Preferably, the energy body is composed of a plurality of energy bars, the plurality of energy bars are dispersed in the matrix layer, and a splicing surface formed by splicing the energy bars and the matrix layer is formed on the surface of the energy base layer, on which the conductive metal layer is deposited; the area of the energy body on the splicing surface accounts for 5% -50%.
Preferably, the energy body is an elastomer with elastic potential energy, and the energy body is used for releasing the elastic potential energy when the temperature is triggered so as to push out the conductive metal deposited on the surface of the energy body out of the conductive metal layer.
Preferably, the energy body comprises a fixed part with a melting point being a trigger temperature and an elastic part with elastic potential energy, and the elastic modulus of the fixed part is larger than that of the elastic part when the elastic potential energy is not released so as to stabilize the elastic part; the elastic part is used for releasing elastic potential energy when the temperature is triggered so as to eject the conductive metal deposited on the surface of the elastic part out of the conductive metal layer and form elastic bulges protruding out of the substrate layer.
Preferably, the thickness of the conductive metal layer is less than or equal to the height of the elastic bump; the fixing part is polyethylene oxide and/or polyethylene with a melting point of 85-130 ℃; the elastic modulus of the elastic part is 0.1-50 MPa, and the elastic part is at least one of polyurethane thermoplastic elastomer, polyester thermoplastic elastomer, polyacrylate thermoplastic elastomer, olefin copolymer elastomer, silicone rubber, fluororubber and natural rubber.
Preferably, the fixing part and the elastic part obtain the energy body through a coextrusion compounding process; the fixing part and the elastic part are arranged in a lamination mode, and at least two layers are arranged.
The second object of the present invention is to provide a method for preparing the composite current collector, comprising the following steps:
s1, attaching an energy body to the surface of a substrate layer, hot-pressing to enable the energy body to store energy and at least partially embed the energy body into the substrate layer, and maintaining pressure, cooling and shaping to obtain an energy base layer;
s2, depositing a conductive metal layer on at least one surface of the energy base layer obtained in the step S1 to obtain the composite current collector.
Preferably, in step S1, the hot pressing treatment is: heating at the temperature 10-30 ℃ higher than the triggering temperature, rolling at the pressure of more than or equal to 5MPa, enabling energy bodies to store energy and at least partially embed into the matrix layer, and then cooling and shaping at the same pressure for the pressure maintaining time of more than or equal to 5min.
A third object of the present invention is to provide an electrode sheet comprising the composite current collector described in any one of the above.
The fourth object of the present invention is to provide a secondary battery comprising a positive electrode sheet, a negative electrode sheet and a separator interposed between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet and/or the negative electrode sheet are/is the electrode sheet.
Compared with the prior art, the invention has the beneficial effects that: according to the composite current collector provided by the invention, the energy body stored with energy is embedded in the matrix layer, when the temperature of the battery reaches the trigger temperature of 85-130 ℃, the energy body releases the pre-stored energy, the conductive metal on the surface of the battery is ejected out and occupies the position, and the ejected conductive metal is separated from the conductive metal layer, so that the purpose of crushing the conductive metal layer is achieved. According to the invention, before thermal runaway, the conductive metal layer is broken into mutually independent small blocks, so that short-circuit current is blocked, heat accumulation is cut off from the source, thermal runaway of the battery core is avoided, and the thermal runaway problem caused by poor thermal conductivity of the traditional composite current collector is solved.
Drawings
Fig. 1 is a schematic structural diagram of the composite current collector before energy release.
Fig. 2 is a schematic diagram of the structure of the composite current collector after energy release.
Fig. 3 is a schematic diagram of the preparation flow and trigger energy release of the composite current collector of the invention.
In the figure: 1-an energy base layer; 11-a substrate layer; 12-energy body; 2-a conductive metal layer; 3-elastic protrusions.
Detailed Description
In order to make the technical scheme and advantages of the present invention more apparent, the present invention and its advantageous effects will be described in further detail below with reference to the detailed description and the accompanying drawings, but the embodiments of the present invention are not limited thereto.
1. Composite current collector
A first aspect of the present invention is directed to a composite current collector, as shown in fig. 1 to 2, comprising an energy base layer 1 and a conductive metal layer 2 deposited on at least one surface of the energy base layer 1; the energy base layer 1 comprises a base layer 11 and an energy body 12 which is at least partially embedded in the base layer 11 and stores energy; the energy body 12 is used for releasing stored energy at a triggering temperature, so that the conductive metal deposited on the surface of the energy body is ejected out of the conductive metal layer 2, the triggering temperature is 85-130 ℃, and the melting point of the substrate layer 11 is higher than the triggering temperature.
According to the composite current collector provided by the invention, the temperature at which thermal runaway of the battery is likely to occur is used as the trigger temperature, and at the trigger temperature, the energy body 12 which is embedded in the matrix layer 11 in advance and stores energy is released, and the conductive metal deposited on the surface of the energy body 12 is ejected out of the conductive metal layer 2, so that the conductive metal layer 2 is broken into mutually independent small blocks, short-circuit current is blocked, heat accumulation is cut off from the source, the thermal runaway of the battery is avoided, the passing rate of abuse tests such as hot box, overcharge, high-temperature short circuit and the like is improved, and the safety performance of the battery is ensured. Under the condition that the battery works normally, the energy body 12 is always embedded in the matrix layer 11, energy is not released, the conductivity of the conductive metal layer 2 is not influenced by the energy body 12, the advantages of high mass energy density and low probability of burrs generated in the battery core containing the composite current collector are maintained, and the application range of the composite current collector is widened.
The triggering temperature can be determined according to the actually adopted materials, the lowest triggering temperature is set to be 85 ℃, and the energy release can not occur due to the fact that the battery is heated to 80 ℃ temporarily (such as the temperature during formation), so that the daily use of the battery is ensured. The maximum temperature is set to 130 ℃, the temperature is not too high, the situation that the composite current collector is insensitive to temperature response due to the fact that the trigger temperature is too high is avoided, more heat is accumulated, and the risk of thermal runaway of the battery is increased. In addition, according to the method specified in GB31241-2014 safety requirements of lithium ion batteries and battery packs for portable electronic products, the battery hot box test temperature is 130+/-2 ℃, and the triggering temperature can ensure that the composite current collector can be broken and opened in time when the hot box test is carried out, cut off current, and ensure the safety performance of the battery. After determining the trigger temperature, a suitable material is chosen as the base layer 11 to ensure that the melting point of the base layer 11 is greater than the trigger temperature, and that the base layer 11 does not melt with the trigger temperature.
The depth of the energy body 12 embedded in the substrate 11 should be not less than 20% of the thickness thereof, and the thickness of the exposed portion should be less than the thickness of the conductive metal layer 2, so as to ensure that the conductive metal layer 2 is also deposited on the surface of the energy body 12, and the surface of the conductive metal layer 2 is smooth. Preferably, the energy body 12 is embedded in the base layer 11 not less than 70% of its total thickness.
The conductive metal layer 2 can be deposited on the energy base layer 1 by one or more of magnetron sputtering, water electroplating, vacuum evaporation and the like. The conductive metal layer 2 is preferably deposited on two corresponding surfaces of the energy base layer 1, both surfaces being embedded with energy bodies 12.
In some embodiments, the ratio of the thickness of the base layer 11 to the thickness of the conductive metal layer 2 is (2 to 50): 1, and the specific thickness ratio may be (2 to 5): 1, (5 to 10): 1, (10 to 15): 1, (15 to 20): 1, (20 to 25): 1, (25 to 30): 1, (30 to 35): 1, (35 to 40): 1, (40 to 45): 1 or (45 to 50): 1. The thickness ratio of the two is set in the range, so that the effect that the conductive metal layer 2 can not be carried due to the fact that the thickness of the substrate layer 11 is too thin is avoided, and the influence on the energy density of the battery cell due to the fact that the thickness of the substrate layer 11 is too thick is avoided. Preferably, the ratio of the thickness of the base layer 11 to the thickness of the conductive metal layer 2 is (5-20): 1. The thickness of the conductive metal layer 2 defined at this time is the thickness of the single-sided deposition.
In some embodiments, the substrate layer 11 is one or more of Polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), poly-paraphenylene terephthalamide (PPA), polyimide (PI). Preferably, the substrate layer 11 is polyethylene terephthalate (PET) or polypropylene (PP). The materials in the preferred range have higher melting points, better thermal stability and more cost advantage.
In some embodiments, the energy body 12 is composed of a plurality of energy bars, the plurality of energy bars are dispersed in the substrate layer 11, and a splicing surface formed by splicing the energy bars and the substrate layer 11 is formed on the surface of the energy substrate layer 1 on which the conductive metal layer 2 is deposited; the energy bodies 12 are dispersed at all positions of the matrix layer 11 in a strip form, namely, after the conductive metal layer 2 is deposited, the energy bodies 12 are dispersed at all positions of the conductive metal layer 2, and after energy release, the conductive metal deposited on the surfaces of all positions of the energy bodies 12 is ejected, so that the purpose of breaking the conductive metal layer 2 is achieved.
In some embodiments, the energy body 12 has an area ratio of 5% to 50% on the splicing surface. The area of the energy body 12 is set in the range, so that on one hand, the situation that the energy body 12 is too little is avoided, and the breaking effect on the conductive metal layer 2 after energy release is poor; on the other hand, the excessive proportion of the energy body 12 is avoided, and the excessive energy body 12 is difficult to autoclave, so that the preparation of the energy base layer 1 is limited.
In some embodiments, the energy body 12 is an elastomer with elastic potential energy, and the energy body 12 is used for releasing the elastic potential energy when the temperature is triggered, so as to eject the conductive metal deposited on the surface of the energy body out of the conductive metal layer 2.
In some embodiments, the elastomer is composed of a plurality of elastic strips, the plurality of elastic strips are dispersed in the substrate layer 11, and the surface of the energy substrate layer 1 on which the conductive metal layer 2 is deposited forms a splicing surface formed by splicing the elastic strips and the substrate layer 11. The cross-section of the elastic strip may be of any shape that facilitates processing, such as square, triangular or circular. Preferably, the thickness of the elastic strip is less than or equal to 20 mu m, and the elastic strip based on the thickness is favorable for being hot pressed and flattened in the preparation process of the elastic base layer so as to be favorable for the deposition of the conductive metal layer 2.
In some embodiments, the plurality of elastic strands are uniformly distributed throughout the substrate layer 11 in the form of strips, grids, or any other shape, thereby separating a single substrate layer 11 into a plurality of individual pieces.
In some embodiments, the elastomer is present in an area of 5% to 50% on the mating face. Specifically, the content of the active ingredients can be 5% -10%, 10% -15%, 15% -20%, 20% -25%, 25% -30%, 30% -35%, 35% -40%, 40% -45% or 45% -50%. Preferably, the area of the elastomer on the splicing surface accounts for 10% -40%. More preferably, the area of the elastomer on the splicing surface is 20% -30%.
In some embodiments, the energy body 12 includes a fixed portion having a melting point of a trigger temperature and an elastic portion having elastic potential energy, and the elastic modulus of the fixed portion is greater than the elastic potential energy of the elastic portion when the elastic potential energy is not released, so as to stabilize the elastic portion; the elastic part is used for releasing elastic potential energy when the trigger temperature is reached, so that the conductive metal deposited on the surface of the elastic part is ejected out of the conductive metal layer 2, and an elastic bulge 3 protruding out of the substrate layer 11 is formed.
The elastic body formed by the fixing part and the elastic part is utilized, so that the elastic modulus of the fixing part is larger under the normal operation of the battery, and the elastic part can be stabilized; and the trigger temperature is determined by the melting point of the fixing part, when the battery reaches the trigger temperature, namely the melting point of the fixing part is reached, the fixing part begins to soften to a molten state, the elastic modulus is reduced, after the elastic part cannot be stabilized, the elastic part releases the stored elastic potential energy, the conductive metal deposited on the surface of the elastic part is ejected out of the conductive metal layer 2, the elastic part occupies the position to form an elastic bulge 3 protruding out of the substrate layer 11, and the ejected conductive metal is separated from the conductive metal layer 2, so that the purpose of breaking the conductive metal layer 2 is achieved.
In some embodiments, the thickness of the conductive metal layer 2 is less than or equal to the height of the elastic bump 3. After the elastic part is ejected to form the elastic bulge 3, the height of the elastic bulge 3 is larger than or equal to the thickness of the conductive metal layer 2, so that the conductive metal deposited on the elastic part can be better separated from the conductive metal at other positions, and the current flow is blocked. Preferably, the thickness of the conductive metal layer 2 is smaller than the height of the elastic bump 3.
In some embodiments, the anchoring portion is polyethylene oxide and/or polyethylene having a melting point of 85-130 ℃. Of course, the fixing part can also be made of other polymer materials with the melting point of 85-130 ℃.
In some embodiments, the elastic modulus of the elastic part is 0.1 to 50MPa, and the elastic part is at least one of polyurethane thermoplastic elastomer, polyester thermoplastic elastomer, polyacrylate thermoplastic elastomer, olefin copolymer elastomer, silicone rubber, fluororubber, and natural rubber.
In some embodiments, the fixing portion and the elastic portion are laminated and at least two layers are provided, and the elastic body is obtained through a coextrusion compounding process. Namely, the extruders respectively carrying the fixed part raw material and the elastic part raw material are simultaneously extruded into the same die head to form the laminated composite material elastomer.
Preferably, the fixing portion and the elastic portion are alternately stacked, and each of them is provided with at least three layers. The elastic body with the multilayer structure has larger contact area between the elastic part and the fixing part, can limit the deformation of the elastic part at room temperature, and better avoids the advanced release of elastic potential energy. More preferably, the fixing portions and the elastic portions are alternately laminated, and each of the fixing portions and the elastic portions is provided with at least four layers.
The preparation method comprises the following steps: respectively throwing the fixed part and the elastic part into two extruders of the multilayer extrusion system, adjusting the rotation speed ratio of the extruders to 1:1, and respectively controlling the temperatures of all sections of the corresponding extruders to be as follows: 40-60 ℃, 165-185 ℃, 180-200 ℃ and 180-200 ℃; 70-90 ℃, 165-185 ℃, 180-200 ℃ and 180-200 ℃. After materials in the extruder are melted and plasticized, two strands of melt are overlapped in a confluence device with double flow channels to obtain an initial structure with the layer number of 2 layers, and then the initial structure flows out of an outlet die with rectangular flow channels after being cut and layered overlapped by a plurality of layer multipliers, wherein the temperatures of the confluence device, the layer multipliers and the outlet die are all about 190 ℃, and the laminated energy body is obtained through pressing of a three-roller calender and traction of a traction machine. If more stacked structures are desired, the above process is repeated.
The second aspect of the present invention is directed to a method for preparing the composite current collector, as shown in fig. 3, comprising the steps of:
s1, attaching an energy body 12 to the surface of a substrate layer 11, and performing hot pressing to enable the energy body 12 to store energy and be at least partially embedded into the substrate layer 11, so as to obtain an energy base layer 1 by pressure maintaining, cooling and shaping;
s2, depositing a conductive metal layer 2 on at least one surface of the energy base layer 1 obtained in the step S1 to obtain the composite current collector.
In some embodiments, the bonding may be gluing or thermal bonding, such that the energy body 12 and the base layer 11 form a whole, and then the energy body 12 is stored with energy and is partially embedded in the base layer 11 by hot pressing, and the two are combined again.
In some embodiments, in step S1, the autoclave is: heating at a temperature 10-30 ℃ higher than the triggering temperature, rolling at a pressure of more than or equal to 5MPa, enabling the energy body 12 to store energy and at least partially embed into the matrix layer 11, and then cooling and shaping at the same pressure for a pressure maintaining time of more than or equal to 5min.
Preferably, for the energy body 12 being an elastomer, the autoclave process may specifically be: firstly, heating the composite film of the matrix layer 11 and the elastomer, wherein the heating temperature is 10-30 ℃ higher than the triggering temperature; then rolling under the pressure of more than or equal to 5MPa to reduce the height of the elastomer and embed the elastomer into the matrix layer 11, compressing the elastomer to have elastic potential energy, then cooling under the same pressure, and keeping the pressure for more than or equal to 5min to achieve the purpose of shaping the elastomer. Wherein the elastomer height is reduced by at least 20% upon hot pressing.
Wherein, the temperature higher than the triggering temperature is adopted for heating, which is favorable for softening the fixed part, so that the elastic part is easier to be embedded into the substrate layer 11; then cooling is carried out under a certain pressure, and the fixed part is solidified to have a larger elastic modulus, so that the elastic part can be stabilized. By matching with the alternate lamination structure of the fixing part and the elastic part, the deformation of the elastic part at room temperature can be better limited by the fixing part after cooling, and the advanced release of elastic potential energy is avoided.
2. Electrode plate
The third aspect of the invention provides an electrode sheet comprising the composite current collector.
In some embodiments, the electrode sheet is a positive electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector, the positive electrode current collector is the composite current collector of the present invention, wherein the conductive metal layer may be aluminum foil.
The positive electrode active material layer comprises a positive electrode active material which is commonly used in lithium ion batteries at present, and comprises, but is not limited to, a chemical formula such as Li x Ni h Co y M z O 2-d N d (wherein, x is more than or equal to 0.95 and less than or equal to 1.2, h)>0，y≥0，z≥0And h+y+z=1, 0.ltoreq.d.ltoreq.1, M is selected from a combination of one or more of Mn, al, N is selected from a combination of one or more of F, P, S), the positive electrode active material may also be a combination of one or more of compounds including but not limited to LiCoO 2 、LiNiO 2 、LiVO 2 、LiCrO 2 、LiMn 2 O 4 、LiCoMnO 4 、Li 2 NiMn 3 O 8 、LiNi 0.5 Mn 1.5 O 4 、LiCoPO 4 、LiMnPO 4 、LiFePO 4 、LiNiPO 4 、LiCoFSO 4 、CuS 2 、FeS 2 、MoS 2 、NiS、TiS 2 And the like. The positive electrode active material may be further subjected to a modification treatment, and a method for modifying the positive electrode active material should be known to those skilled in the art, for example, the positive electrode active material may be modified by coating, doping, or the like, and the material used for the modification treatment may be one or more combinations including, but not limited to, al, B, P, zr, si, ti, ge, sn, mg, ce, W, or the like.
In some embodiments, the electrode sheet is a negative electrode sheet, and the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector, where the negative electrode current collector is the composite current collector according to the present invention, and the conductive metal layer may be a copper foil.
The negative electrode active material layer includes a negative electrode active material, which is currently a common negative electrode active material for lithium ion batteries, including, but not limited to, one or more of graphite, soft carbon, hard carbon, carbon fibers, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals capable of forming alloys with lithium, and the like. Wherein, the graphite can be selected from one or more of artificial graphite, natural graphite and modified graphite; the silicon-based material can be one or more selected from simple substance silicon, silicon oxygen compound, silicon carbon compound and silicon alloy; the tin-based material can be selected from one or more of elemental tin, tin oxide and tin alloy.
3. Secondary battery
A fourth aspect of the present invention is directed to a secondary battery including a positive electrode sheet, a negative electrode sheet, and a separator interposed between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet and/or the negative electrode sheet are/is the electrode sheet described above.
The separator may be a variety of materials suitable for lithium ion battery separators in the art, and may be, for example, a combination of one or more of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, natural fibers, and the like.
The secondary battery further includes an electrolyte including an organic solvent, an electrolyte lithium salt, and an additive. Wherein the electrolyte lithium salt can be LiPF used in high-temperature electrolyte 6 And/or LiBOB; liBF used in the low-temperature electrolyte may be used 4 、LiBOB、LiPF 6 At least one of (a) and (b); liBF used in the overcharge-preventing electrolyte may also be used 4 、LiBOB、LiPF 6 At least one of LiTFSI; liClO may also be 4 、LiAsF 6 、LiCF 3 SO 3 、LiN(CF 3 SO 2 ) 2 At least one of them. And the organic solvent may be a cyclic carbonate, including PC, EC; chain carbonates, including DFC, DMC, or EMC; carboxylic esters, including MF, MA, EA, MP, and the like, are also contemplated. And additives include, but are not limited to, film forming additives, conductive additives, flame retardant additives, overcharge prevention additives, and control of H in electrolytes 2 At least one of an additive for O and HF content, an additive for improving low temperature performance, and a multifunctional additive.
In order to make the technical solution and advantages of the present invention more apparent, the present invention and its advantageous effects will be described in further detail below with reference to the specific embodiments, but the embodiments of the present invention are not limited thereto.
Example 1
A composite current collector comprising an energy base layer and a conductive metal layer deposited on at least one surface of the energy base layer; the energy base layer comprises a base layer and an energy body which is at least partially embedded in the base layer and stores energy; the energy body is used for releasing stored elastic potential energy at a triggering temperature so as to eject conductive metal deposited on the surface of the energy body out of the conductive metal layer, the triggering temperature is 85-130 ℃, and the melting point of the matrix layer is higher than the triggering temperature; the energy body consists of a plurality of energy strips, the energy strips are dispersed in the matrix layer, and the surface of the energy base layer, on which the conductive metal layer is deposited, forms a splicing surface formed by splicing the energy strips and the matrix layer.
The energy body comprises a fixed part with a melting point being a trigger temperature and an elastic part with elastic potential energy, and the elastic modulus of the fixed part is larger than that of the elastic part when the elastic potential energy is not released so as to stabilize the elastic part; the elastic part is used for releasing elastic potential energy when the temperature is triggered so as to eject the conductive metal deposited on the surface of the elastic part out of the conductive metal layer and form elastic bulges protruding out of the substrate layer.
Wherein the matrix layer is a PET matrix layer (the American Dow product, the brand RE5292, the melting point is 252 ℃), and the area ratio of the energy body on the splicing surface is 30%; the elastic part is a polyurethane thermoplastic elastomer (German Basoff product, brand EB95A 12), the fixed part is polyethylene oxide (American Dow product, brand POLYOX WSR N10, the melting point is 87 ℃, namely the triggering temperature of the embodiment is 87 ℃), the number of layers after the elastic part and the fixed part are co-extruded and compounded is 8 (4 layers of the elastic part and the fixed part respectively), and the cross section shape is square; the conductive metal layer is a copper layer.
The preparation method of the composite current collector comprises the following steps:
1) Extruding the elastic part and the fixed part by adopting a coextrusion composite process to obtain a strip-shaped energy body, wherein the thickness is 3 mu m, and the width is 1mm; bonding the energy body with a 6 μm thick substrate layer; heating to 100deg.C, rolling under 8MPa to reduce the thickness of the energy body protruding from the matrix layer to below 0.5 μm, cooling and maintaining pressure for 6 min at the same time to shape to obtain energy base layer;
2) Copper foils with the thickness of 1 mu m are respectively deposited on two sides of the obtained energy base layer in a magnetron sputtering mode to serve as conductive metal layers, and the composite current collector is prepared.
And applying the obtained composite current collector to a negative plate.
The preparation method of the negative electrode sheet comprises the following steps: taking water as a solvent, and mixing graphite, a thickening agent and an SBR binder according to the mass ratio of 97.7:1.1:1.2, uniformly mixing to prepare lithium ion battery negative electrode slurry with solid content of 50% and certain viscosity, coating one side surface of the composite current collector, drying and rolling at 80 ℃, and then coating and drying the negative electrode slurry on the other side of the composite copper foil according to the method to obtain the negative electrode plate with both sides coated with active substances.
The obtained negative electrode plate is applied to a lithium ion battery, and the preparation method of the lithium ion battery comprises the following steps:
1) Preparing a positive plate:
the positive electrode active material, the conductive agent (a mixture of conductive carbon black and carbon nano tubes in a mass ratio of 6:5), the PVDF binder and NMP are uniformly mixed according to a mass ratio of 97.6:1.1:1.3:35 to prepare positive electrode slurry. Coating positive electrode slurry on one side of a current collector aluminum foil, drying and rolling at 85 ℃, coating and drying the positive electrode slurry on the other side of the current collector aluminum foil according to the method, and carrying out cold pressing treatment on a positive electrode sheet with the positive electrode active material layer coated on both sides; and then trimming and slitting are carried out to prepare the positive plate of the lithium ion battery.
2) Preparation of electrolyte:
lithium hexafluorophosphate (LiPF) 6 ) Dissolved in a mixed solvent of dimethyl carbonate (DMC), ethylene Carbonate (EC) and methyl ethyl carbonate (EMC) (the mass ratio of DMC, EC and EMC is 3:5:2) to obtain an electrolyte.
3) Preparation of the battery:
and winding the prepared positive plate, negative plate and diaphragm into a battery core, wherein the capacity of the battery core is about 5Ah. The diaphragm is positioned between the adjacent positive plate and the negative plate, the positive electrode is led out by spot welding of an aluminum tab, and the negative electrode is led out by spot welding of a nickel tab; and then placing the battery core in an aluminum-plastic packaging bag, baking, injecting the electrolyte, and finally preparing the lithium ion battery through the procedures of packaging, formation, capacity division and the like.
Example 2
Different from example 1, the elastic part of this example was a styrene-polybutadiene-styrene block copolymer elastomer (SBS) purchased from the name Vandex under the trade name F675.
The remainder is the same as embodiment 1 and will not be described here again.
Example 3
The number of layers of the elastomer was 2 layers, i.e., one layer each of the elastic portion and the fixing portion, in this example, unlike example 1.
The remainder is the same as embodiment 1 and will not be described here again.
Example 4
The number of layers of the elastomer was 4 layers, namely, two layers of each of the elastic portion and the fixing portion in this example, unlike example 1.
The remainder is the same as embodiment 1 and will not be described here again.
Example 5
Unlike example 1, the elastomer area was a 20% area on the splice face of the energy body in this example.
The remainder is the same as embodiment 1 and will not be described here again.
Example 6
Unlike example 1, the area of the elastomer was 2% in this example.
The remainder is the same as embodiment 1 and will not be described here again.
Example 7
Unlike example 1, the elastomer area was a 5% area on the splice face.
The remainder is the same as embodiment 1 and will not be described here again.
Example 8
Unlike example 1, the area of the elastomer was 50% of the area of the energy body on the splice face in this example.
The remainder is the same as embodiment 1 and will not be described here again.
Example 9
Unlike example 1, the fixing portion was selected so that the ratio of the thickness of the base layer to the thickness of the conductive metal layer was 4.5:1 (the thickness of the base layer was 4.5 μm, and the thickness of the conductive metal layer was 1 μm).
The remainder is the same as embodiment 1 and will not be described here again.
Example 10
Unlike example 1, the fixing portion was selected so that the ratio of the thickness of the base layer to the thickness of the conductive metal layer was 20:1 (the thickness of the base layer was 20 μm, and the thickness of the conductive metal layer was 1 μm).
The remainder is the same as embodiment 1 and will not be described here again.
Example 11
Unlike example 1, the material of the fixing part was polyethylene (melting point 110 ℃, i.e., trigger temperature 110 ℃ in this example, commercially available from exxon mobil, brand LD100 AC).
The preparation method of the composite current collector comprises the following steps:
1) Extruding the elastic part and the fixed part by adopting a coextrusion composite process to obtain a strip-shaped energy body, wherein the thickness is 3 mu m, and the width is 1mm; bonding the energy body with a 6 μm matrix layer; heating to 125 ℃, rolling under 8MPa to reduce the thickness of the energy body protruding from the substrate layer to below 0.5 mu m, cooling and maintaining the pressure for 6 minutes at the same time, and shaping to obtain an energy base layer;
2) Copper foils with the thickness of 1 mu m are respectively deposited on two sides of the obtained energy base layer in a magnetron sputtering mode to serve as conductive metal layers, and the composite current collector is prepared.
The remainder is the same as embodiment 1 and will not be described here again.
Example 12
Unlike embodiment 1, the conductive metal layer of this embodiment is an aluminum layer.
And applying the obtained composite current collector to a positive plate.
The preparation method of the positive plate comprises the following steps: the positive electrode active material, the conductive agent (a mixture of conductive carbon black and carbon nano tubes in a mass ratio of 6:5), the PVDF binder and NMP are uniformly mixed according to a mass ratio of 97.6:1.1:1.3:35 to prepare positive electrode slurry. Coating the positive electrode slurry on one side of the composite current collector, drying and rolling at 85 ℃, coating and drying the positive electrode slurry on the other side of the composite current collector according to the method, and carrying out cold pressing treatment on the positive electrode plate with the positive electrode active material layer coated on both sides; and then trimming and slitting are carried out to prepare the positive plate of the lithium ion battery.
The positive plate is applied to a lithium ion battery, and the current collector of the negative plate of the lithium ion battery is a common copper foil.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 1
The difference from example 1 is the choice of fixing part, polycaprolactone in this comparative example with a melting point of 60℃and from Perston, sweden, number 6800.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 2
The difference from example 1 is the choice of material for the fixing part, which is polypropylene with a melting point of 165℃and is available from Yanshan petrochemicals under the brand K1001.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 3
The difference from example 1 is that the fixing portion is selected so that the ratio of the thickness of the base layer to the thickness of the conductive metal layer in this comparative example is 1:1 (the thicknesses of the base layer and the conductive metal layer are 1 μm).
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 4
The comparative example is a conventional composite current collector, which does not have a thermal trigger deformation function, and is 1 μm copper plating layer+6 μm PET layer+1 μm copper plating layer.
The lithium ion batteries obtained in examples 1 to 12 and comparative examples 1 to 4 were subjected to hot box, overcharge and high temperature short circuit performance test.
The hot box performance test method comprises the following steps: according to the method prescribed in GB31241-2014 safety requirements of lithium ion batteries and battery packs for portable electronic products, the battery cells are charged to 4.45V at constant current and constant voltage of 0.7C and cut-off multiplying power of 0.02C, then the fully charged battery cells are placed in an oven, the temperature of the oven is increased at the temperature rising rate of (5+/-2) DEG C/min, the battery cells are kept for 30min after the temperature in the oven reaches 130+/-2 ℃, and the battery cells are not fired and pass the test.
The overcharge performance test method comprises the following steps: and discharging the battery cell to 3.0V at a constant current of 0.5C, then charging to 4.8V at a constant current and constant voltage of 3.0C, and ending the test when the continuous charging time of the battery cell reaches 7h or the temperature of the battery cell is reduced to 20% lower than the peak value. In the test process, the voltage, current and temperature change data of the battery core need to be recorded, the temperature measuring point is positioned at the center of the maximum surface of the battery core, the battery core does not fire, explosion is avoided, or the highest temperature of the surface of the battery core is less than or equal to 150 ℃ and passes the test.
The high-temperature short circuit performance test method comprises the following steps: discharging the battery cell to 3.0V at a constant current of 0.5C, charging to 4.45V at a constant current and constant voltage of 0.7C, cutting off the power of 0.02C, placing the fully charged battery cell in an oven at 55+/-2 ℃, standing for 30min after the surface temperature of the battery cell reaches 55+/-5 ℃, shorting the positive electrode and the negative electrode of the battery cell by using a load with a resistance value of 60+/-10 mΩ, monitoring the surface temperature and the voltage of the battery cell, and ending the test when the temperature of the battery cell is reduced to be 20% lower than the peak value or the shorting time reaches 24 hours. The battery cell does not get on fire, does not explode or the highest temperature of the surface of the battery cell is less than or equal to 130 ℃ and passes the test.
The test results are shown in Table 1 below.
TABLE 1
As can be seen from the comparison of the results in table 1, compared with comparative example 4, after the energy bodies are introduced into the composite current collector, the hot box, overcharge and high-temperature short circuit performances are obviously improved, especially, the hot box test at 130 ℃ is carried out, the test passing rate is improved from 0% to 100%, and the safety performance of the lithium ion battery applying the composite current collector is obviously improved.
In addition, as can be seen from the test results of comparative example 1, since the melting point is set too low, the deformation of the elastic member in the composite current collector is recovered during the processing of the cell, the conductive layer is broken into separate small pieces, resulting in a large increase in the internal resistance of the cell, and the passing rate of each test is 100%, but the deterioration of the electrical performance of the cell is all at the cost, and the cell has no practicality. It can be seen from the test result of comparative example 2 that the deformation of the elastic member is not recovered due to the excessively high melting point, the due function of the elastic member cannot be exerted, the thermal box, the overcharge and the high-temperature short-circuit performance test cannot be passed, and the safety performance of the battery is low. Based on the above, the triggering temperature of the composite current collector is set between 85 ℃ and 130 ℃, the melting point is not too low and too high, and the battery has good electrochemical performance while the safety performance of the battery is improved.
In addition, as can be seen from the comparison between the embodiment 1 and the embodiments 3 to 4, the fixing portion and the elastic portion with more layers are provided, the fixing portion and the elastic portion have more contact areas, the elastic portion can be better limited from recovering under the normal operation of the battery, the phenomenon that the internal resistance of the battery core is increased and the effect of cutting off the short-circuit current is poor due to the fact that a part of elastic portion is released and recovered in advance due to the fact that the layers are too small is avoided, and the test passing rate is lower than that of the embodiment 1 as can be seen from the test results.
It can also be seen from a comparison of examples 1, 5 to 8 that the reasonable setting of the elastomer to elastomeric base layer ratio prevents the elastomer from being too small to break the conductive metal layer into a plurality of small pieces independent of each other, and the blocking effect is reduced, as in the test results of example 6. Particularly, when the area of the preferable elastic body is 20% -30% of the area of the elastic base layer, the passing rate of the hot box, overcharge and high-temperature short-circuit performance test can be effectively improved, and the safety performance of the battery is ensured.
As is clear from examples 1, 9 to 10 and comparative example 3, when the ratio of the base layer to the conductive metal layer is too small, the base layer is extremely easily deformed during the metal deposition process, and a usable composite current collector cannot be obtained. Preferably, when the ratio of the matrix layer to the conductive metal layer is 4.5:1-6:1, good processability can be ensured, and the energy density of the battery cell can be improved.
In summary, the composite current collector provided by the invention introduces the energy body capable of releasing energy at the triggering temperature, and the conductive metal layer can be broken into independent small blocks by releasing the energy, so that the passing rate of the battery thermal box, overcharge and high-temperature short-circuit performance test is increased, the safety performance of the battery is improved, the application range of the composite current collector is widened, and the problem of thermal runaway caused by poor thermal conductivity of the conventional composite current collector is effectively solved.
Variations and modifications of the above embodiments will occur to those skilled in the art to which the invention pertains from the foregoing disclosure and teachings. Therefore, the present invention is not limited to the above-described embodiments, but is intended to be capable of modification, substitution or variation in light thereof, which will be apparent to those skilled in the art in light of the present teachings. In addition, although specific terms are used in the present specification, these terms are for convenience of description only and do not limit the present invention in any way.
Claims (11)
1. A composite current collector, comprising:
an energy base layer comprising a base layer and an energy body at least partially embedded in the base layer and storing energy;
a conductive metal layer deposited on at least one surface of the energy base layer;
the energy body is used for releasing stored energy when the triggering temperature is 85-130 ℃ so as to eject the conductive metal deposited on the surface of the energy body out of the conductive metal layer, and the melting point of the matrix layer is higher than the triggering temperature.
2. The composite current collector of claim 1, wherein the ratio of the thickness of said base layer to the thickness of said conductive metal layer is (2-50): 1; the matrix layer is one or more of polyethylene, polypropylene, polyethylene terephthalate, polyethylene naphthalate, poly-p-phenylene terephthalamide and polyimide.
3. The composite current collector of claim 1, wherein the energy body is composed of a plurality of energy bars, the plurality of energy bars are dispersed in a matrix layer, and a splicing surface formed by splicing the energy bars and the matrix layer is formed on the surface of the energy base layer on which the conductive metal layer is deposited; the area of the energy body on the splicing surface accounts for 5% -50%.
4. A composite current collector according to any one of claims 1 to 3 wherein the energy body is an elastomer having elastic potential energy for releasing the elastic potential energy at a trigger temperature to eject the conductive metal deposited on its surface out of the conductive metal layer.
5. The composite current collector according to claim 4, wherein the energy body comprises a fixed portion having a melting point of a trigger temperature and an elastic portion having elastic potential energy, and an elastic modulus of the fixed portion is greater than that of the elastic portion when the elastic potential energy is not released to stabilize the elastic portion; the elastic part is used for releasing elastic potential energy when the temperature is triggered so as to eject the conductive metal deposited on the surface of the elastic part out of the conductive metal layer and form elastic bulges protruding out of the substrate layer.
6. The composite current collector of claim 5 wherein the thickness of said conductive metal layer is less than or equal to the height of said resilient protrusions; the fixing part is polyethylene oxide and/or polyethylene with a melting point of 85-130 ℃; the elastic modulus of the elastic part is 0.1-50 MPa, and the elastic part is at least one of polyurethane thermoplastic elastomer, polyester thermoplastic elastomer, polyacrylate thermoplastic elastomer, olefin copolymer elastomer, silicone rubber, fluororubber and natural rubber.
7. The composite current collector according to claim 5, wherein the fixing portion and the elastic portion obtain an energy body through a coextrusion compounding process; the fixing part and the elastic part are arranged in a lamination mode, and at least two layers are arranged.
8. A method of manufacturing a composite current collector according to any one of claims 1 to 7, comprising the steps of:
s1, attaching an energy body to the surface of a substrate layer, hot-pressing to enable the energy body to store energy and at least partially embed the energy body into the substrate layer, and maintaining pressure, cooling and shaping to obtain an energy base layer;
s2, depositing a conductive metal layer on at least one surface of the energy base layer obtained in the step S1 to obtain the composite current collector.
9. The method for manufacturing a composite current collector according to claim 8, wherein in step S1, the hot pressing process is: heating at a temperature 10-30 ℃ higher than the triggering temperature, rolling at a pressure of more than or equal to 5MPa, enabling energy bodies to store energy and at least partially embed into the matrix layer, and then cooling and shaping at the same pressure for a pressure maintaining time of more than or equal to 5min.
10. An electrode sheet comprising the composite current collector of any one of claims 1 to 7.
11. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a separator interposed between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet and/or the negative electrode sheet is the electrode sheet of claim 10.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311134878.XA CN117199385A (en) | 2023-09-05 | 2023-09-05 | Composite current collector, preparation method thereof, electrode plate and secondary battery |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311134878.XA CN117199385A (en) | 2023-09-05 | 2023-09-05 | Composite current collector, preparation method thereof, electrode plate and secondary battery |
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| Publication Number | Publication Date |
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| CN117199385A true CN117199385A (en) | 2023-12-08 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN202311134878.XA Pending CN117199385A (en) | 2023-09-05 | 2023-09-05 | Composite current collector, preparation method thereof, electrode plate and secondary battery |
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| Country | Link |
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| CN (1) | CN117199385A (en) |
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2023
- 2023-09-05 CN CN202311134878.XA patent/CN117199385A/en active Pending
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