CN118156408A

CN118156408A - Secondary battery and electronic device

Info

Publication number: CN118156408A
Application number: CN202410346719.4A
Authority: CN
Inventors: 任文臣; 张丽娟
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2024-03-25
Filing date: 2024-03-25
Publication date: 2024-06-07

Abstract

The application provides a secondary battery and an electronic device, and belongs to the technical field of batteries. The secondary battery of the application comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode active material layer; the negative electrode active material layer includes silicon-containing active particles; the aspect ratio of the silicon-containing active particles is a, the compacted density of the anode active material layer is B, and a and B satisfy: (A x B) is more than or equal to 1.83 and less than or equal to 2.89. By controlling the synergistic relationship between the aspect ratio of the silicon-containing active particles in the negative electrode plate and the compaction density of the negative electrode active material layer, the synergistic effect between the shape of the silicon-containing active particles and the processing pressure is fully exerted, the breakage of the silicon-containing active particles is reduced, and further, the side reaction between the silicon-containing active particles and the electrolyte is reduced, so that the cycle performance and the safety of the secondary battery are improved.

Description

Secondary battery and electronic device

Technical Field

The application belongs to the technical field of batteries, and particularly relates to a secondary battery and an electronic device.

Background

With the rapid development of the fields of electric vehicles, portable electronic devices, etc., the demand for higher performance batteries is increasing. The silicon-containing anode has higher active material intercalation/deintercalation capacity (3579 mAh/g), and compared with the traditional carbon anode material (372 mAh/g), the specific capacity of the silicon-containing anode can be several times higher, or even more. This means that a silicon doped battery can store more lithium ions at the same volume and weight, providing a higher electrical energy storage density. However, the silicon-containing negative electrode has the problems of large volume change, high electrochemical activity and the like in practical application, and is easy to react with electrolyte to cause capacity loss, so that the development and the application of the silicon-containing negative electrode are restricted.

The prior art proposes to deposit nano silicon in a porous carbon material, and to provide an expansion space for silicon particles by using the porous carbon material, and to improve the volume effect of a silicon-containing anode to a certain extent by matching with a smaller volume change rate of the nano silicon material, but the cycle performance of a secondary battery still needs to be further improved.

Disclosure of Invention

In view of the above, the present application provides a secondary battery for solving the problem of poor cycle performance of the secondary battery having a silicon-containing anode in the prior art, and also has higher safety performance. The second aspect of the present application provides an electronic device including the secondary battery.

In order to solve the above-described problems, the present application provides, in a first aspect, a secondary battery including a negative electrode tab including a negative electrode active material layer; the negative electrode active material layer includes silicon-containing active particles; the aspect ratio of the silicon-containing active particles was A, the compacted density of the anode active material layer was B g/cc, and A and B satisfied: (A x B) is more than or equal to 1.83 and less than or equal to 2.89. The silicon-containing active particles in the negative electrode plate are controlled to be matched with the compaction density of the negative electrode active material layer, and the silicon-containing active particles are reduced from cracking in the rolling process and the charging expansion process of the negative electrode plate through the synergistic effect of the silicon-containing active particles and the negative electrode plate, so that the silicon-containing active particles have lower specific surface area, side reactions of the silicon-containing active particles and electrolyte are reduced, the loss of active materials is reduced, the internal resistance and heat generation of the secondary battery are reduced, the cycle performance of the secondary battery is improved, and the safety and reliability are also improved.

More preferably, 1.0.ltoreq.A.ltoreq.1.7. On the basis of meeting the relation A multiplied by B, the range of the aspect ratio of the silicon-containing active particles is controlled, the anisotropism of the particles is reduced, the silicon-containing active particles can be promoted to be uniformly stressed during rolling, and the breakage or crushing of the particles is further reduced, so that the side reaction between the internal active silicon exposure and electrolyte after the particles are crushed is reduced, and the higher capacity retention rate of the secondary battery is favorably maintained.

More preferably, 1.70.ltoreq.B.ltoreq.1.83. On the basis of satisfying the above-mentioned a×b relationship, the compaction density of the anode active material layer is controlled, so that the components in the active material layer are sufficiently contacted, breakage of the silicon-containing active particles is further reduced, and the cycle performance and safety performance of the secondary battery are further improved. Further, B is more than or equal to 1.75 and less than or equal to 1.80, so that the secondary battery has better cycle performance and safety performance.

More preferably, a and B satisfy: (A x B) is more than or equal to 1.83 and less than or equal to 2.14. The secondary battery in this range can further improve the cycle performance and safety performance of the secondary battery by matching the aspect ratio of the silicon-containing active particles with the compacted density of the anode active material layer.

More preferably, the sphericity of the silicon-containing active particles having a diameter of more than 10 μm is 0.81 to 0.98. The application can further ensure that the silicon-containing active particles are uniformly stressed in the anode active material layer by controlling the sphericity of the silicon-containing active particles and matching with the aspect ratio and the compaction density of the anode active material layer, reduce or avoid the problem that the silicon-containing active particles are easily crushed due to uneven stress when stressed, and further optimize the cycle performance and the safety performance of the secondary battery.

More preferably, the mass fraction of Si element is 43-55% based on the silicon-containing active particles. In some embodiments, the mass fraction of Si element is 2.1% to 22% based on the anode active material layer.

More preferably, the silicon-containing active particles are prepared by a process comprising the steps of: step S100, carrying out gradient heating and heat preservation treatment on a mixture of a carbon source and alkali to obtain a porous carbon material; and step 200, introducing silane gas into the porous carbon material in an inert gas atmosphere to react, and thus obtaining the silicon-containing active particles.

More preferably, the gradient temperature-increasing and heat-preserving treatment includes: heating the mixture of the carbon source and the alkali to 350-550 ℃ for heat preservation for 15-45 min, and then heating to 600-900 ℃ for heat preservation for 0.5-2 h.

More preferably, the carbon source is selected from at least one of phenolic resin, coal, biomass material, petroleum coke.

More preferably, the carbon source has an aspect ratio of 1.0 to 1.8.

More preferably, the secondary battery satisfies at least one of the conditions a to c: the Dv50 particle diameter of the silicon-containing active particles satisfies the condition a: dv50 is less than or equal to 5.6 mu m and less than or equal to 10.4 mu m; the true density of the silicon-containing active particles under the condition b is 1.853g/cc to 2.108g/cc; condition c, the anode active material layer further includes a carbon material; the carbon material comprises artificial graphite and/or natural graphite. The application controls the Dv50 particle diameter of the silicon-containing active particles in a proper range, can ensure proper transmission distance of lithium ions and electrons in the particles, simultaneously reduces the outer surface of the silicon-containing active particles, further reduces side reaction with electrolyte, and ensures the coulombic efficiency and the cycle performance of the secondary battery. On the other hand, the application controls the true density of the silicon-containing active particles to ensure that the active particles have proper pores, thereby accommodating the volume expansion of the internal nano silicon, ensuring higher silicon content and improving the energy density of the secondary battery.

In a second aspect, the present application also provides an electronic device, including any one of the secondary batteries described above.

Based on the secondary battery provided by the application, the synergistic effect between the shape of the silicon-containing active particles and the processing pressure is fully exerted by limiting the synergistic relationship between the aspect ratio A of the silicon-containing active particles and the negative electrode active material layer compaction density B, so that the secondary battery is prevented from losing active materials caused by exposing active silicon in the silicon-containing active particles and carrying out side reaction with air or electrolyte due to crushing of the silicon material particles in a negative electrode rolling procedure, the capacity retention rate and the cycle performance of the secondary battery are improved, the internal resistance and the internal heat generation of the secondary battery can be reduced due to reduction of side reaction, and the secondary battery has higher safety performance; the application further controls the sphericity of the silicon-containing active particles with the diameter larger than 10 mu m to match with the parameters, can avoid the silicon-containing active particles from being broken in the anode active material layer due to uneven stress, and further improves the cycle performance and the safety performance of the secondary battery.

Drawings

Fig. 1 is an SEM image of silicon-containing active particles provided in example 1 of the present application.

Detailed Description

The present application will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present application more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application.

For simplicity, the present application discloses only a few numerical ranges specifically. However, any lower limit may be combined with any upper limit to form a range not explicitly recited; and any lower limit may be combined with any other lower limit to form a range not explicitly recited, and any upper limit may be combined with any other upper limit to form a range not explicitly recited. Furthermore, each separately disclosed point or individual value may itself be combined as a lower limit or upper limit with any other point or individual value or with other lower limit or upper limit to form a range not explicitly recited.

In the description of the present application, "above", "below" includes this number unless otherwise indicated.

Unless otherwise indicated, terms used in the present application have well-known meanings commonly understood by those skilled in the art. Unless otherwise indicated, the numerical values of the parameters set forth in the present application may be measured by various measurement methods commonly used in the art (e.g., may be tested according to the methods set forth in the examples of the present application).

In the present application, the list of items to which the term "at least one of," "at least one of," or other similar terms are connected may mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means only a; only B; or A and B. In another example, if items A, B and C are listed, the phrase "at least one of A, B and C" means only a; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item a may comprise a single component or multiple components. Item B may comprise a single component or multiple components. Item C may comprise a single component or multiple components.

In the present application, the term "silicon-containing active particles" refers to a negative electrode material containing silicon element in a solid particle state, for example, a silicon-carbon composite material in a solid particle state. In some exemplary embodiments, the silicon-containing active particles include porous carbon particles having pores, and silicon formed inside the porous carbon particles and/or on the surface of the porous carbon particles.

The application is further described below in conjunction with the detailed description. It should be understood that the detailed description is intended by way of illustration only and is not intended to limit the scope of the application.

The silicon-containing negative electrode has higher specific capacity, so that higher electric energy storage density can be provided, but the compaction density of the silicon-containing negative electrode is smaller than that of the traditional graphite negative electrode during actual processing, so that the high-capacity advantage of the silicon negative electrode can not be fully exerted, and the volume energy density of the secondary battery is limited in lifting amplitude.

The inventors of the present application found in the course of the study that since the deformability of the silicon anode upon compaction is weaker than that of graphite and the shape of conventional silicon anode particles is irregular, the silicon anode particles are liable to be broken due to uneven stress when the rolling pressure is increased. The broken silicon negative electrode particles react with moisture or oxygen in the air before the secondary battery is assembled, so that the capacity of the silicon negative electrode is reduced, the silicon negative electrode particles react with electrolyte irreversibly after the secondary battery is assembled, solvents and lithium salts of the electrolyte are consumed, trace water, gas and other harmful substances are possibly generated, the internal resistance of the secondary battery is obviously increased due to insufficient side reaction layers and electrolyte generated on the surfaces of the silicon particles, and more Joule heat is generated when the positive electrode and the negative electrode are short-circuited, so that the safety risk of the secondary battery is increased.

In order to solve the problem that silicon anode particles are easy to break during rolling, the inventor of the application discovers that when means of reducing anode rolling pressure, optimizing particle size distribution, reducing doping amount of silicon in graphite and the like are adopted, the reduction of rolling pressure and silicon doping amount can reduce the volume capacity of the anode and finally reduce the volume energy density of a secondary battery, and the optimization of particle size distribution can only reduce the breaking amount of silicon particles, so that the problem cannot be thoroughly solved.

In view of the above, the present application provides a secondary battery including a negative electrode tab including a negative electrode active material layer; the negative electrode active material layer includes silicon-containing active particles; the aspect ratio of the silicon-containing active particles is a, the compacted density of the anode active material layer is B, and a and B satisfy: (A x B) is more than or equal to 1.83 and less than or equal to 2.89. The application fully exerts the synergistic effect between the shape of the material and the processing pressure by limiting the synergistic relationship between the aspect ratio A of the silicon-containing active particles and the rolling density B during the processing of the negative electrode, avoids crushing the secondary battery due to the silicon material particles in the rolling process of the negative electrode, reduces the internal resistance and heat generation of the secondary battery, and improves the safety performance of the secondary battery; the exposure of active silicon inside the silicon particles is reduced, so that side reactions with air or electrolyte can be reduced, thereby improving the first efficiency of the secondary battery and ensuring the capacity retention rate of the secondary battery during the cycle.

In some embodiments, 1.83.ltoreq.A.ltoreq.B.ltoreq.2.14 may further improve cycle performance and safety performance of the secondary battery. In some embodiments, the product of the silicon-containing active particle aspect ratio a and the negative electrode compacted density B may be a value in the range of 1.83, 1.93, 2.04, 2.06, 2.10, 2.14, 2.16, 2.18, 2.20, 2.49, 2.89, or any two of these values. When (a×b) > 2.89, the silicon-containing active particles are broken when the negative electrode is rolled, fresh interfaces generated by the breakage contain a large amount of high-activity nano silicon, a series of side reactions (reaction with air, reaction with electrolyte, etc.) of nano silicon can cause an increase in irreversible electrochemical reaction, a large amount of non-conductive byproducts accumulated on the electrode surface can increase the internal resistance of the secondary battery and generate more joule heat, thereby deteriorating the coulombic efficiency of the secondary battery, remarkably deteriorating the cycle performance and the safety performance capacity retention rate of the secondary battery. When (a×b) <1.83, insufficient contact points between particles of the active material layer may occur, and the resistance of the negative electrode coating layer increases, resulting in degradation of the conductive electron and ion transport properties of the negative electrode, thereby degrading various properties of the secondary battery in charge and discharge.

In some embodiments, the aspect ratio A of the silicon-containing active particles is in the range of 1.0.ltoreq.A.ltoreq.1.7. For example, a may be a value within a range of 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or any two of these values. When the aspect ratio of the silicon-containing active particles is greater than 1.7, the anisotropy of the silicon-containing active particles increases, and the particles are easily broken due to uneven stress during rolling, and after the particles are broken under pressure, the active silicon in the silicon-containing particles is exposed and reacts with electrolyte side-ways, thereby affecting the cycle performance of the secondary battery.

In some embodiments, the negative electrode active material layer has a compacted density B in the range of 1.70 g/cc.ltoreq.B.ltoreq.1.83 g/cc. For example, B may be a value within a range of 1.70, 1.71, 1.72, 1.73, 1.74, 1.75, 1.76, 1.77, 1.78, 1.79, 1.80, 1.81, 1.82, 1.83, or any two of these values. The compaction density of the anode active material layer is controlled, so that all components in the active material layer are fully contacted, the ion or electron transmission is facilitated, the dynamic performance of the secondary battery is improved, the breakage of silicon-containing active particles is reduced, the lithium storage capacity of the anode is improved, and the cycle performance and the safety performance of the secondary battery are further improved. In some embodiments, B is 1.75.ltoreq.B.ltoreq.1.80, which may further improve the cycle performance and the safety performance of the secondary battery.

In some embodiments, the sphericity of silicon-containing active particles having a diameter greater than 10 μm is from 0.81 to 0.98. For example, the sphericity of the silicon-containing active particles having a diameter greater than 10 μm may be a value within a range of 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, or any two of these values. By controlling the sphericity of the silicon-containing active particles having a diameter of more than 10 μm in combination with the aspect ratio thereof and the compacted density of the anode active material layer, the cycle performance and safety performance of the secondary battery can be further improved. In some embodiments, the Dv50 particle size of the silicon-containing active particles satisfies: dv50 is less than or equal to 5.6 mu m and less than or equal to 10.4 mu m. When Dv50 is too low, the silicon-containing active particles have a large number of outer surfaces, and the SEI film formed by these outer surfaces undergoes more irreversible side reactions and consumes more electrolyte, thereby affecting the coulombic efficiency and cycle performance of the secondary battery. If Dv50 is too high, the transport distance of lithium ions and electrons in the particles increases, and the charge/discharge rate of the secondary battery becomes slow.

In some embodiments, the silicon-containing active particles have a true density of 1.853g/cc to 2.108g/cc. When the true density is too low, the silicon-containing active particles contain a large number of pores, and the amount of the substance participating in the electrochemical reaction per unit volume decreases, resulting in insufficient capacity density of the secondary battery. When the true density is too high, pores in the silicon-containing active particles are less and too dense, and the volume expansion generated when the nano silicon in the silicon-containing active particles is expanded can not be absorbed by the pores, so that the structural stability of the silicon-containing active particles is affected.

In some embodiments, the silicon-containing active particles have a gram capacity of 1485.5mAh/g to 1804.2mAh/g and a first coulombic efficiency of 79.2% to 87.7%.

In some embodiments, the silicon-containing active particles provided herein are prepared by a process comprising the steps of: step S100, carrying out gradient heating and heat preservation treatment on a mixture of a carbon source and alkali to obtain a porous carbon material; and step 200, introducing silane gas into the porous carbon material in an inert gas atmosphere to react, and thus obtaining the silicon-containing active particles.

In some embodiments, the aspect ratio of the carbon source is between 1.0 and 1.8, for example, can be a value in the range of 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or any two of these values. The aspect ratio of the silicon-containing active particles can be regulated and controlled by controlling the aspect ratio of the carbon source, and the silicon-containing active particles with higher aspect ratio can be obtained by adopting the carbon source with the aspect ratio to be matched with gradient heating and heat preservation treatment, and the silicon-containing active particles and the negative electrode active material layer are matched with each other to generate synergistic effect, so that the cycle performance and the safety performance of the secondary battery are further improved.

In some embodiments, after the reaction of introducing the silane gas in step S200 is completed, an alkyne gas is introduced into the porous carbon material to ensure the purity of the silicon particles deposited in the porous carbon.

In some embodiments, the method of preparing the silicon-containing active particles comprises the steps of: step S100, mixing 1000g of phenolic resin microspheres with potassium hydroxide according to the proportion of alkali to carbon ratio of 3:1, and then carrying out gradient heating and heat preservation treatment on the mixture, wherein the gradient heating and heat preservation treatment comprises the following steps: the mixture was first treated in a rotary kiln at 450℃for 30min, then the rotary kiln temperature was raised to 750℃and incubated for 45min. And (3) after the gradient heating and heat preservation treatment, the obtained product is subjected to acid washing, water washing and drying to obtain the porous carbon material. And step 200, adding 1000g of the porous carbon into a fluidized bed reactor, heating to 480 ℃ under the nitrogen atmosphere of 10L/min, preserving heat for 4 hours, and then introducing the silane gas of 2.5L/min for 280min. After stopping the silane feeding, heating the fluidized bed reactor to 500 ℃ and preserving heat for 1h, then feeding 5L/min of acetylene gas for 300min, and obtaining the silicon-containing active particles after the reaction is finished.

In some embodiments, the anode active material layer further comprises a carbon material; the carbon material comprises artificial graphite and/or natural graphite. Alternatively, the mass ratio of the silicon-containing active particles to graphite in the anode active material layer is 1 (5 to 12), preferably 1 (8 to 10).

In some embodiments, the negative electrode sheet is prepared by a method comprising the steps of: mixing a negative electrode active material (silicon-containing active particles and graphite are mixed according to a mass ratio of 1:9, the mixing gram capacity of the negative electrode active material is controlled to be 480 mAh/g), a carbon nano tube, lithium carboxymethyl cellulose and lithium polyacrylate according to a mass ratio of 97.4:0.2:0.4:2, adding deionized water serving as a solvent, and obtaining negative electrode slurry under the action of a vacuum stirrer, wherein the solid content of the negative electrode slurry is 45wt% and the viscosity is 600 Pa.s. And (3) coating the negative electrode slurry on one surface of a negative electrode current collector copper foil with a certain thickness, and drying the copper foil at 80 ℃ to obtain a negative electrode plate with a coating weight of 100.1mg/1540.25mm ² and a negative electrode material layer coated on one side. And repeating the steps on the other surface of the copper foil to obtain the negative electrode plate with the double-sided coating negative electrode material layer. Then cold pressing, cutting and slitting are carried out to obtain the negative pole piece with the specification of 661mm multiplied by 78 mm.

In some embodiments, the anode active material layer further includes a binder and/or a conductive agent. In some embodiments, in the anode active material layer, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethyleneoxy-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylic or acrylated styrene-butadiene rubber, epoxy or nylon, and the like.

In some embodiments, the conductive agent includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

The secondary battery of the present application further includes a positive electrode including a positive electrode current collector and a positive electrode active material layer including a positive electrode active material, a binder, and a conductive agent.

According to some embodiments of the application, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel alloy, titanium alloy, silver alloy, or the like) on a polymer substrate.

According to some embodiments of the application, the positive electrode active material includes at least one of lithium cobaltate, lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel type lithium manganate, spinel type lithium nickel manganate, and lithium titanate. In some embodiments, in the positive electrode active material layer, the binder includes a binder polymer, such as at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefin, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber, or polyurethane. In some embodiments, the polyolefin-based binder comprises at least one of polyethylene, polypropylene, polyolefin ester, polyalkylene alcohol, or polyacrylic acid. In some embodiments, the conductive agent comprises a carbon-based material, such as carbon black, acetylene black, ketjen black, or carbon fiber; metal-based materials such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

The secondary battery of the present application further includes a separator, and the material and shape of the separator used in the secondary battery of the present application are not particularly limited, and may be any of the techniques disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic, etc., formed from a material that is stable to the electrolyte of the present application. For example, the release film may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is at least one selected from polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected.

The surface treatment layer is provided on at least one surface of the base material layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or may be a layer formed by mixing a polymer and an inorganic substance. The inorganic layer includes inorganic particles and a binder, the inorganic particles being at least one selected from the group consisting of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is at least one selected from polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer is at least one selected from polyamide, polyacrylonitrile, acrylic polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride and poly (vinylidene fluoride-hexafluoropropylene).

The secondary battery of the present application further includes an electrolyte. The electrolyte in the present application includes an organic solvent, a lithium salt, and optional additives. In some embodiments, the organic solvent includes, but is not limited to: ethylene Carbonate (EC), propylene Carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate. In some embodiments, the organic solvent comprises an ether-type solvent, for example, comprising at least one of 1, 3-Dioxapentacyclic (DOL) and ethylene glycol dimethyl ether (DME). In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, lithium salts include, but are not limited to: lithium hexafluorophosphate (LiPF ₆), lithium tetrafluoroborate (LiBF ₄), lithium difluorophosphate (LiPO ₂F₂), lithium bis (trifluoromethanesulfonyl) imide LiN (CF ₃SO₂)₂ (LiTFSI), lithium bis (fluorosulfonyl) imide Li (N (SO ₂F)₂) (LiFSI), lithium bis (oxalato) borate LiB (C ₂O₄)₂ (LiBOB), or lithium difluorooxalato borate LiBF ₂(C₂O₄) (lidaob).

According to some embodiments of the application, the secondary battery of the application includes, but is not limited to: lithium ion batteries or sodium ion batteries. In some embodiments, the secondary battery comprises a lithium ion battery.

The present application further provides an electronic device comprising the secondary battery of the present application.

The electronic device or apparatus of the present application is not particularly limited. In some embodiments, the electronic device of the present application includes, but is not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, cellular telephones, portable fax machines, portable copiers, portable printers, headsets, video recorders, liquid crystal televisions, hand-held cleaners, portable CD players, mini-compact discs, transceivers, electronic notepads, calculators, memory cards, portable audio recorders, radios, backup power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting fixtures, toys, gaming machines, watches, power tools, flashlights, cameras, home-use large storage batteries, lithium ion capacitors, and the like.

The following will describe the embodiments of the present application with reference to specific examples and comparative examples. In the following examples and comparative examples, reagents, materials and instruments used, unless otherwise specified, were commercially available.

Example 1

The lithium ion battery of the embodiment comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode active material layer; the negative electrode active material layer includes silicon-containing active particles; the aspect ratio a of the silicon-containing active particles was 1.2, and the compacted density B of the anode active material layer was 1.70g/cc, a×b=2.04.

The lithium ion battery of the embodiment is prepared by a method comprising the following steps:

< preparation of porous carbon >

Phenolic resin microspheres were used as a carbon source, wherein the aspect ratio of the phenolic resin microspheres was 1.3. Mixing 1000g of phenolic resin microspheres with potassium hydroxide according to the proportion of alkali to carbon ratio of 3:1, firstly treating for 30min at 450 ℃ in a rotary furnace, then raising the temperature of the rotary furnace to 750 ℃ and preserving the temperature for 45min. And (3) carrying out acid washing, water washing and drying on the obtained product to obtain the porous carbon material.

< Preparation of silicon-containing active particles >

Adding 1000g of porous carbon into a fluidized bed reactor, heating to 480 ℃ under the nitrogen atmosphere of 10L/min, preserving heat for 4 hours, and then introducing monosilane gas of 2.5L/min for 280 minutes. After stopping introducing silane gas, heating the fluidized bed reactor to 500 ℃ and preserving heat for 1h, then introducing 5L/min of acetylene gas for 300min, and obtaining the silicon-containing active particles with the aspect ratio A of 1.2 after the reaction is finished. FIG. 1 is an SEM image of a silicon-containing active particle according to example 1 of the present application, wherein the sphericity of the silicon-containing active particle having a diameter of greater than 10 μm is 0.81, the Dv50 particle size of the silicon-containing active particle is 7.8 μm, and the true density of the silicon-containing active particle is 2.040g/cc. The mass fraction of Si element is 46.2% based on the silicon-containing active particles.

< Preparation of negative electrode sheet >

Mixing a negative electrode active material (silicon-containing active particles and graphite are mixed according to a mass ratio of 1:9, the mixing gram capacity of the negative electrode active material is controlled to be 480 mAh/g), a carbon nano tube, lithium carboxymethyl cellulose and lithium polyacrylate according to a mass ratio of 97.4:0.2:0.4:2, adding deionized water serving as a solvent, and obtaining negative electrode slurry under the action of a vacuum stirrer, wherein the solid content of the negative electrode slurry is 45wt% and the viscosity is 600 Pa.s. The negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil with the thickness of 6 mu m, and the copper foil is dried at 80 ℃ to obtain a negative electrode plate with a coating weight of 100.1mg/1540.25mm ² and a negative electrode material layer coated on one side. And repeating the steps on the other surface of the copper foil to obtain the negative electrode plate with the double-sided coating negative electrode material layer. The compaction density of the negative electrode active material layer is controlled to be 1.70g/cc in the cold pressing process, and the negative electrode plate with the specification of 661mm multiplied by 78mm can be obtained after cutting and slitting.

In the anode active material layer, the mass fraction of Si element was 4.5% based on the anode active material layer.

< Preparation of Positive electrode sheet >

Mixing an anode active material LiCoO ₂, conductive carbon black serving as a conductive agent and polyvinylidene fluoride serving as a binder according to the mass ratio of 96.7:1.7:1.6, adding N-methyl pyrrolidone (NMP), and obtaining anode slurry under the action of a vacuum stirrer, wherein the solid content of the anode slurry is 76wt%. The positive electrode slurry is uniformly coated on one surface of a positive electrode current collector aluminum foil with the thickness of 9 mu m, and the aluminum foil is dried at 120 ℃ to obtain a positive electrode plate with a coating weight of 260mg/1540.25mm ² and a positive electrode material layer coated on one side. And repeating the steps on the other surface of the aluminum foil to obtain the positive electrode plate with the double-sided coating positive electrode material layer. Then cold pressing, cutting and cutting to obtain the positive pole piece with the specification of 661mm multiplied by 76.5 mm.

< Preparation of electrolyte >

Mixing FEC, EC, PC, EMC and DEC according to the mass ratio of 5:10:15:20:50 in an argon atmosphere glove box with the water content of less than 10ppm to obtain an organic solvent, then adding lithium salt LiPF ₆ into the organic solvent, and uniformly mixing to obtain the electrolyte. Wherein the mass percentage of the lithium salt LiPF ₆ is 12.5 percent.

< Separation Membrane >

A porous polyethylene film (supplied by Celgard Co.) having a thickness of 10 μm was used.

< Preparation of lithium ion Battery >

And sequentially stacking the prepared positive electrode plate, the isolating film and the negative electrode plate, so that the isolating film is positioned between the positive electrode plate and the negative electrode plate to play a role in isolation, and winding to obtain the electrode assembly. And placing the electrode assembly in an aluminum plastic film packaging bag, drying, injecting electrolyte, and performing vacuum packaging, standing, formation, degassing, trimming and other procedures to obtain the lithium ion battery.

Example 2

The lithium ion battery of this example was different from example 1 only in that the compacted density of the negative electrode active material layer was 1.72g/cc in cold pressing of the negative electrode tab.

Example 3

The lithium ion battery of this example was different from example 1 only in that the compacted density of the negative electrode active material layer was 1.75g/cc in cold pressing of the negative electrode tab.

Example 4

The lithium ion battery of this example was different from example 1 only in that the compacted density of the negative electrode active material layer was 1.78g/cc in cold pressing of the negative electrode tab.

Example 5

The lithium ion battery of this example was different from example 1 only in that the compacted density of the negative electrode active material layer was 1.80g/cc in cold pressing of the negative electrode sheet.

Example 6

The lithium ion battery of this example was different from example 1 only in that the compacted density of the negative electrode active material layer was 1.83g/cc in cold pressing of the negative electrode tab.

Example 7

The lithium ion battery of this example was different from example 1 only in that the aspect ratio of the prepared silicon-containing active particles was 1.0, and the compacted density of the negative electrode active material layer in cold pressing of the negative electrode sheet was 1.83g/cc.

Example 8

The lithium ion battery of this example differs from example 1 only in that the aspect ratio of the silicon-containing active particles produced was 1.1, and in cold pressing of the negative electrode sheet, the compacted density of the negative electrode active material layer was 1.75g/cc.

Example 9

The lithium ion battery of this example differs from example 1 only in that the aspect ratio of the silicon-containing active particles produced was 1.4, and the compacted density of the negative electrode active material layer in cold pressing of the negative electrode sheet was 1.78g/cc.

Example 10

The lithium ion battery of this example was different from example 1 only in that the aspect ratio of the prepared silicon-containing active particles was 1.7, and in cold pressing of the negative electrode sheet, the compacted density of the negative electrode active material layer was 1.7g/cc as in example 1.

Example 11

The lithium ion battery of this example differs from example 1 only in that the sphericity of the silicon-containing active particles having a diameter of more than 10 μm is 0.87.

Example 12

The lithium ion battery of this example differs from example 1 only in that the sphericity of the silicon-containing active particles having a diameter of more than 10 μm is 0.95.

Example 13

The lithium ion battery of this example differs from example 1 only in that the sphericity of the silicon-containing active particles having a diameter of more than 10 μm is 0.98.

Comparative example 1

The lithium ion battery of this comparative example was different from example 1 only in that the aspect ratio of the prepared silicon-containing active particles was 1.7, and the compacted density of the anode active material layer in cold pressing of the anode electrode sheet was 1.82g/cc.

Comparative example 2

The lithium ion battery of this comparative example differs from example 5 only in that the aspect ratio of the silicon-containing active particles produced is 1.8.

Comparative example 3

The lithium ion battery of this comparative example differs from example 6 only in that the aspect ratio of the silicon-containing active particles produced is 1.8.

Comparative example 4

The lithium ion battery of this comparative example was different from example 1 only in that the aspect ratio of the prepared silicon-containing active particles was 2.3, and the compacted density of the negative electrode active material layer in cold pressing of the negative electrode sheet was 1.7g/cc as in example 1.

Comparative example 5

The lithium ion battery of this comparative example was different from example 7 only in that the compacted density of the anode active material layer was 1.68g/cc in cold pressing of the anode electrode sheet.

Comparative example 6

The lithium ion battery of this comparative example differs from example 1 only in that the aspect ratio of the silicon-containing active particles produced is 1.5.

Test examples

The following test methods were used to test various parameters or properties of the lithium ion batteries of the examples and comparative examples of the present application:

1. Particle aspect ratio test

And photographing the particles by using a scanning electron microscope, measuring the longest diameter L (the distance between the two farthest points of the edges of the particle projection surface) on the particle projection surface and the longest diameter W on the particle projection surface perpendicular to the longest diameter L, and calculating the ratio of L/W to obtain the aspect ratio of the particles.

2. Sphericity test

The sphericity of the material is tested by an equivalent diameter method, wherein the test method is to observe silicon-containing active particles in powder or pole pieces by using a ZEISS-SEM (sigma-02-33) scanning electron microscope, remove incomplete particles, and calculate the perimeter equivalent diameter and the particle area equivalent diameter of the complete particles.

Sphericity = circumference equivalent diameter/area equivalent diameter.

3. True density testing

According to the Azithro principle, the real volume of the measured material is accurately measured by using the Bohr's law (PV=nRT) of small molecular helium under certain conditions, so that the real density of the measured material is obtained, and the test equipment is an AccuPyc II1340 real density tester.

4. Diameter of silicon-containing active particles

The image analysis method is used for testing, and a ZEISS-SEM (sigma-02-33) scanning electron microscope is used for shooting microscopic images of silicon-containing active particles in the powder or the pole piece in a back scattering mode. And carrying out edge recognition on the silicon-containing active particles in the image by using imageJ software, then calculating the equivalent projection area of each particle, and calculating the area equivalent diameter of each particle according to the equivalent projection area to obtain the diameter of the silicon-containing active particles.

5. Gram Capacity test

Silicon-containing active particles, a conductive agent (conductive carbon black, abbreviated as SP), a binder (lithiated polyacrylic acid, abbreviated as PAA-Li), carbon Nanotubes (CNTs) and a dispersing agent (CMC) are mixed according to a mass ratio of 84:10:5:0.4:0.6, and deionized water is added to obtain the cathode slurry with the solid content of 48%. And uniformly mixing the negative electrode slurry, coating the mixture on a copper foil, and drying, cold pressing and punching to obtain the negative electrode plate.

In a glove box with water oxygen content less than 10ppm, methyl ethyl carbonate (EMC), ethylene Carbonate (EC) and diethyl carbonate (DEC) are mixed according to the mass ratio of 1:1:1 to obtain a mixed solvent, and then lithium salt LiPF ₆ and fluoroethylene carbonate (FEC) are added, and the electrolyte is obtained after uniform mixing. Wherein, based on the mass of the electrolyte, the mass percent of the lithium salt LiPF ₆ is 12.5 percent, and the mass percent of the FEC is 4 percent.

And in a glove box with the water and oxygen contents of less than 10ppm, assembling the negative electrode plate, the counter electrode metal lithium plate, a polypropylene (PP) diaphragm and the electrolyte into a button cell.

Gram Capacity test: after the button cell was allowed to stand at 25℃for 6 hours, it was discharged to 5mV at a current of 0.05C, then discharged to 5mV at a current of 50. Mu.A, after 5 minutes of standing, it was discharged to 5mV at a current of 10. Mu.A, and after 5 minutes of standing, it was charged to 0.8V at a rate of 0.05C. The above discharge capacity was designated as G ₀, and the charge capacity was designated as G ₁.

Wherein gram capacity = G ₁; first coulombic efficiency = G ₁/G₀ x 100%.

6. Lithium ion battery cycle performance and thickness expansion rate test

And placing the lithium ion battery in a constant temperature test box at 25 ℃, and standing for 30min to enable the lithium ion battery to reach a constant temperature state at 25 ℃. Constant current charging is carried out at 1C to 4.53V, constant voltage charging is carried out to current of 0.025C, standing is carried out for 5min, constant current discharging is carried out at 0.5C to 3.0V, and initial discharge capacity is recorded as C ₀. With this step cycled 400 turns, the discharge capacity after 400 turns of recording cycle was C ₁.

Capacity retention after 400 cycles = C ₁/C₀ x 100%.

7. Compaction density test of negative electrode active material layer

And measuring the thickness of the rolled negative electrode plate by using a micrometer, and measuring the thickness calculation average value of any 12 different positions to obtain the thickness value h ₃ of the negative electrode plate. And (3) punching the formed negative electrode plate with a circular cutter to obtain a wafer with the area of 1540.25mm ², weighing on a balance with the resolution precision of ten thousandth, repeating the punching/weighing steps for 5 times, and taking the average value of the weighed weight to obtain the weight m ₃ of the wafer. The thickness h ₂ of the pure copper foil and the wafer weight m ₂ of the pure copper foil having an area of 1540.25mm ² were obtained by taking the pure copper foil and using the same method as described above.

The compacted density Q ₁＝(m₃-m₂)/(h₃-h₂)/1540.25 of the anode active material layer.

8. Short circuit test of lithium ion battery

Placing 10 lithium ion batteries in a constant temperature test box at 25 ℃, and standing for 30min to enable the lithium ion batteries to reach a constant temperature state at 25 ℃. Charging to 4.53V with 1C constant current, charging to 0.02C constant voltage, and standing for 5min. And shorting the anode and the cathode of the lithium ion battery by using a load resistor of 80+/-20 mΩ, and observing the appearance and the temperature change of the lithium ion battery. If all 10 lithium ion batteries are not leaked, smoke is not emitted, fire is not generated, explosion is not generated, and the surface temperature of the battery core is not higher than 150 ℃, the short circuit test is passed, and if the lithium ion batteries do not meet the indexes, the short circuit test is not passed.

The various parameters and performance characterization results obtained by the above tests for the lithium ion batteries of examples 1 to 10 and comparative examples 1 to 6 provided by the present application are shown in table 1 below.

TABLE 1

From the performance characterization results of table 1, it is understood that examples 1 to 10 control the aspect ratio a of the silicon-containing active particles in the anode sheet and the compacted density B of the anode active material layer to satisfy 1.83 (axb) 2.89, and the capacity retention of the lithium ion battery after 400 cycles can reach 89.6% to 94.5%, and pass all short circuit tests. In contrast, the a×b values of comparative examples 1 to 6 were outside the defined range, the capacity retention was only 76.5 to 88.7%, and the short circuit test could not be passed. Among them, the value of a×b in comparative examples 1 to 4 exceeds the defined range, resulting in significant deterioration of capacity retention of the lithium ion battery after 400 cycles. This is mainly because too high aspect ratio or too high compaction density can cause a large number of silicon-containing active particles to be crushed and broken, and fresh interfaces generated after the crushing undergo a large number of side reactions, so that active silicon and electrolyte are rapidly consumed, and meanwhile, a large number of byproducts generated by the reaction of the electrolyte and the active silicon can increase the impedance of a negative electrode, and a large amount of joule heat is generated under a large current of a short circuit test, so that the internal temperature of a battery is too high and safety failure is caused. In comparative examples 5 to 6, the a×b value was lower than the limit range, and the contact between particles in the negative electrode active material layer was not tight, and the negative electrode was not able to effectively exert capacity due to the increase in resistance, so that the capacity retention rate of the lithium ion battery after 400 cycles was also low. The application can control the aspect ratio of the silicon-containing active particles in the negative electrode plate, and the compaction density of the negative electrode active material layer is less than or equal to 1.83 (A multiplied by B) and less than or equal to 2.89, so that the silicon-containing active particles and the negative electrode active material layer are cooperatively matched, and the cycle performance and the safety performance of the lithium ion battery can be effectively improved.

As a preferred mode, examples 1 to 4 and examples 7 to 8 control a and B to satisfy: the capacity retention rate of the lithium ion battery after 400 circles can reach 91.3-94.5%, and the cycle performance of the lithium ion battery is further improved.

According to the application, through the matching of the aspect ratio of the silicon-containing active particles and the solid density of the negative electrode active material layer, the side reaction of the silicon-containing active particles is obviously inhibited, the phenomenon of increasing the impedance of the negative electrode is controlled, so that the capacity retention rate of the lithium ion battery after circulation is improved, the generated Joule heat is limited during short circuit test, and the safety performance of the lithium ion battery is good.

The various parameters and performance characterization results obtained by the above tests for the lithium ion batteries of examples 1, 11-13 provided by the present application are shown in table 2 below.

TABLE 2

As is clear from table 2, the lithium ion batteries of examples 1 and 11 to 13 further preferably have a sphericity of silicon-containing active particles having a diameter of more than 10 μm, and by matching the shape characteristics with the aspect ratio and the compacted density of the anode active material layer, it is possible to further ensure uniform stress of the silicon-containing active particles in the anode active material layer, reduce or avoid the problem that the silicon-containing active particles are easily crushed due to uneven stress at the time of stress, and the obtained lithium ion battery has a capacity retention of 93.8% to 95.2% after 400 cycles and has excellent cycle performance. Wherein, examples 11 to 13, on the basis of the aspect ratio A of the silicon-containing active particles in the negative electrode sheet and the compaction density B of the negative electrode active material layer, further match the sphericity of the silicon-containing active particles with the diameter larger than 10 μm to reach 0.87 to 0.98, and can further improve the cycle performance of the lithium ion battery while ensuring the safety performance of the lithium ion battery.

Claims

1. A secondary battery comprising a negative electrode tab, wherein the negative electrode tab comprises a negative electrode active material layer; the anode active material layer includes silicon-containing active particles;

The aspect ratio of the silicon-containing active particles is A, the compacted density of the negative electrode active material layer is Bg/cc, and A and B satisfy: (A x B) is more than or equal to 1.83 and less than or equal to 2.89.

2. The secondary battery according to claim 1, wherein 1.0.ltoreq.A.ltoreq.1.7.

3. The secondary battery according to claim 1, wherein 1.70.ltoreq.b.ltoreq.1.83.

4. The secondary battery according to claim 3, wherein 1.75.ltoreq.B.ltoreq.1.80.

5. The secondary battery according to claim 1, wherein a and B satisfy: (A x B) is more than or equal to 1.83 and less than or equal to 2.14.

6. The secondary battery according to any one of claims 1to 5, wherein the sphericity of the silicon-containing active particles having a diameter of more than 10 μm is 0.81 to 0.98.

7. The secondary battery according to claim 1, wherein the mass fraction of Si element is 43% to 55% based on the silicon-containing active particles.

8. The secondary battery according to claim 1, wherein the silicon-containing active particles are prepared by a method comprising the steps of:

step S100, carrying out gradient heating and heat preservation treatment on a mixture of a carbon source and alkali to obtain a porous carbon material;

And step 200, introducing silane gas into the porous carbon material in an inert gas atmosphere to react, so as to obtain the silicon-containing active particles.

9. The secondary battery according to claim 8, wherein the gradient temperature-increasing and heat-preserving process comprises: heating the mixture of the carbon source and the alkali to 350-550 ℃ for heat preservation for 15-45 min, and then heating to 600-900 ℃ for heat preservation for 0.5-2 h; and/or the number of the groups of groups,

The carbon source is at least one selected from phenolic resin, coal, biomass material and petroleum coke; and/or the number of the groups of groups,

The aspect ratio of the carbon source is 1.0 to 1.9.

10. The secondary battery according to claim 1, wherein the secondary battery satisfies at least one of the conditions a to c:

the Dv50 particle diameter of the silicon-containing active particles satisfies the condition a: dv50 is less than or equal to 5.6 mu m and less than or equal to 10.4 mu m;

The true density of the silicon-containing active particles under the condition b is 1.853g/cc to 2.108g/cc;

Condition c, the anode active material layer further includes a carbon material; the carbon material comprises artificial graphite and/or natural graphite.

11. An electronic device comprising the secondary battery according to any one of claims 1 to 10.