Patent Application
20230369563
The present disclosure relates to the technical field of lithium-ion batteries, and in particular, to a negative electrode sheet including a silicon-based material and optionally a carbon-based material, and a lithium-ion battery including the negative electrode sheet.
Lithium-ion batteries have the advantages of long cycle life, low self-discharge rate and being environmentally friendly, and have been widely used in notebook computers, mobile phones, cameras, and other consumer electronics. A lithium-ion battery is mainly composed of a positive electrode, a negative electrode, a separating membrane, and an electrolyzing solution, the negative electrode material of the lithium-ion battery, as an important component thereof, is vital for the lithium-ion battery.
The negative electrode material of the lithium-ion battery is mainly composed of graphite, hard carbon, silicon, silicon oxide, tin, etc. Silicon-based negative electrode has high gram capacity and rich content, and is an important material for high energy density batteries. However, a solid electrolyte interphase film on a surface of the silicon-based negative electrode is continuously consumed, the cycle life of the battery is thus affected, resulting in a main bottleneck that limits the application of the silicon-based negative electrode, especially, the continuous consumption of the solid electrolyte interphase film on the surface of the silicon-based negative electrode results in the deterioration of battery performance. Thus, how to improve the cycle performance of the silicon-based negative electrode is particularly important.
In order to improve the shortcomings that a silicon-based negative electrode material has a continuous consumption of a solid electrolyte interphase film and has side reactions that directly affect the effective transmission of lithium-ions and electrons inside an electrode sheet during charging and discharging processes in the prior art, the present disclosure provides a negative electrode sheet and a lithium-ion battery including same. The negative electrode sheet can effectively improve the transmission of lithium-ions and electrons, form a solid electrolyte interphase film having a stable structure, inhibit volume change of the negative electrode sheet, and improve the cycling performance of the silicon-based negative electrode, especially the cycling performance of the silicon-based negative electrode at room temperature.
The purpose of the present disclosure is achieved through the following technical solution:
R1-R-M-R′-R′1, Formula 1,
For a silicon-based material in a negative electrode of a conventional battery system, with the charging and discharging of the battery, there are alloying and dealloying of lithium-ions in the silicon-based negative electrode, resulting in irregular expansion of the volume of the silicon-based material, and thus, more interphases are generated to produce a solid electrolyte interphase film, therefore, a large amount of solvent and auxiliary agent are consumed. An auxiliary agent containing a carbon-carbon double bond or a carbon-carbon triple bond for the negative electrode is used in the present disclosure, and the carbon-carbon double bond or carbon-carbon triple bond undergoes electrochemical polymerization at a low potential, and thus, a stable solid electrolyte interphase film is formed in the silicon-based negative electrode, thereby effectively slowing down the occurrence of side reactions on the interphases of the silicon-based material, reducing the increase of internal resistance during a battery cycling process, and improving battery cycle performance.
According to the present disclosure, each of R1 and R′1 is a terminal group, and at least one of R1 and R′1 includes at least one of the following groups as the terminal group: —O—(C═O)—C(R2)═C(R′2)(R′2), —N(R3)—(C═O)—C(R2)═C(R′2)(R′2), —C(R2)═C(R′2)(R′2), where R2 is selected from H or an organic functional group (such as C1-12 alkyl, C3-20 cycloalkyl, 3-20 membered heterocyclic group, C6-18 aryl, 5-20 membered heteroaryl, bridged ring group formed by C3-20 cycloalkyl and C3-20 cycloalkyl, bridged ring group formed by C3-20 cycloalkyl and 3-20 membered heterocyclic group, bridged ring group formed by 3-20 membered heterocyclic group and 3-20 membered heterocyclic group); R′2 are the same or different, and independently selected from H or an organic functional group (such as C1-12 alkyl, C3-20 cycloalkyl, 3-20 membered heterocyclic group, C6-18 aryl, 5-20 membered heteroaryl, bridged ring group formed by C3-20 cycloalkyl and C3-20 cycloalkyl, bridged ring group formed by C3-20 cycloalkyl and 3-20 membered heterocyclic group, bridged ring group formed by 3-20 membered heterocyclic group and 3-20 membered heterocyclic group); R3 is selected from H or C1-3 alkyl.
According to the present disclosure, one or both of R1 and R′1 include one or two of the following groups as the terminal groups: —O—(C═O)—C(R2)═C(R′2)(R′2), —N(R3)—(C═O)—C(R2)═C(R′2)(R′2), —C(R2)═C(R′2)(R′2), —C≡C—R′2; where R2 is selected from H or C1-6 alkyl (for example, selected from H or C1-3 alkyl; for another example, selected from H or methyl); R′2 are the same or different, and independently selected from H or C1-6 alkyl (for example, selected from H or C1-3 alkyl; for another example, selected from H or methyl); R3 is selected from H or C1-3 alkyl.
According to the present disclosure, R and R′ are the same or different, and independently selected from absent, alkylene, —NR3—, where R3 is H or C1-3 alkyl.
In an implementation, R and R′ are the same or different, and independently selected from absent, —CH2—, —CH2CH2—, —NH—, —N(CH3)—, —N(CH2CH3)—.
According to the present disclosure, the polyphenylene ether chain segment has a repeating unit represented by Formula 2:
Specifically, the polyphenylene ether chain segment has a repeating unit represented by Formula 2′:
According to the present disclosure, the polyethylene glycol chain segment has a repeating unit represented by Formula 3:
According to the present disclosure, the polypropylene glycol chain segment has a repeating unit represented by Formula 4:
According to the present disclosure, the polyethanedithiol chain segment has a repeating unit represented by Formula 5:
According to the present disclosure, the polycarbonate chain segment has a repeating unit represented by Formula 6:
According to the present disclosure, the polysiloxane chain segment has a repeating unit represented by Formula 7:
According to the present disclosure, the compound represented by Formula 1 has a number-average molecular weight of 200-3000, in an implementation, the compound represented by Formula 1 has a number-average molecular weight of 300-10000.
According to the present disclosure, the compound represented by Formula 1 is selected from at least one of polyethanedithiol acrylate, polyethanedithiol methacrylate, polyethanedithiol diacrylate, polyethanedithiol dimethyl acrylate, polyethanedithiol phenyl ether acrylate, polyethanedithiol monoallyl ether, polyethylene glycol acrylate, polyethylene glycol methacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polyethylene glycol phenyl ether acrylate, polyethylene glycol monoallyl ether, polycarbonate acrylate, polycarbonate methacrylate, polycarbonate diacrylate, polycarbonate dimethyl acrylate, polycarbonate phenyl ether acrylate, polycarbonate monoallyl ether, polypropylene glycol acrylate, polypropylene glycol methacrylate, polypropylene glycol diacrylate, polypropylene glycol dimethacrylate, polypropylene glycol phenyl ether acrylate, polypropylene glycol monoallyl ether, polysiloxane acrylate, polysiloxane methacrylate, polysiloxane diacrylate, polysiloxane dimethyl acrylate, polysiloxane phenyl ether acrylate, and polysiloxane monoallyl ether.
According to the present disclosure, the negative electrode active material layer includes components with mass percentage contents as following: 75-98 wt % of the negative electrode active material, 1-15 wt % of the conductive agent, 0.999-10 wt % of the binder, and 0.001-2 wt % of the auxiliary agent.
According to the present disclosure, the silicon-based material is selected from at least one of nano silicon, SiOx (0<x<2), aluminum-silicon alloy, magnesium-silicon alloy, boron-silicon alloy, phosphorus-silicon alloy, and lithium-silicon alloy.
According to the present disclosure, the negative electrode active material further includes a carbon-based material, and the carbon-based material is selected from at least one of artificial graphite, natural graphite, hard carbon, soft carbon, mesocarbon microbead, fullerene, and graphene.
In a negative electrode of a conventional battery system, with the charging and discharging of the battery, there are alloying and dealloying of lithium-ions in the negative electrode of the silicon-based material and carbon-based material, resulting in irregular expansion of the volume of the negative electrode sheet, and thus, more interphases are generated to produce a solid electrolyte interphase film, thereof, a large amount of solvent and auxiliary agent are consumed in the electrolyzing solution. An auxiliary agent containing a carbon-carbon double bond or a carbon-carbon triple bond is used in the present disclosure, the carbon-carbon double bond or carbon-carbon triple bond undergoes electrochemical polymerized at a low potential, and thus, a stable solid electrolyte interphase film is formed in the negative electrode of silicon-based material and carbon-based material, thereby effectively slowing down the occurrence of side reactions on the interphases between the silicon-based material and the carbon-based material, reducing the increase of internal resistance during a battery cycling process, and improving battery cycle performance.
According to the present disclosure, the negative electrode active material layer (after rolling) has a thickness of 20 μm-200 μm, in an implementation, the negative electrode active material layer (after rolling) has a thickness of 30 μm-150 μm.
The present disclosure further provides a lithium-ion battery including the above negative electrode sheet.
The beneficial effects of the present disclosure:
Negative Electrode Sheet
As mentioned above, the present disclosure provides a negative electrode sheet including a negative electrode current collector and a negative electrode active material layer coated on one or both surfaces of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, and an auxiliary agent, where the negative electrode active material includes a silicon-based material; the auxiliary agent is selected from at least one of a compound represented by Formula 1:
R1-R-M-R′-R′1, Formula 1,
in Formula 1, M is selected from a polyphenylene ether chain segment, a polyethylene glycol chain segment, a polyethanedithiol chain segment, a polycarbonate chain segment, a polypropylene glycol chain segment, or a polysiloxane chain segment; each of R1 and R′1 is a terminal group, and at least one of R1 and R′1 includes a carbon-carbon double bond or a carbon-carbon triple bond as the terminal group; each of R and R′ is a linking group.
In an embodiment of the present disclosure, each of R1 and R′1 is a terminal group, and at least one of R1 and R′1 includes at least one of the following groups as the terminal group: —O—(C═O)—C(R2)═C(R′2)(R′2), —N(R3)—(C═O)—C(R2)═C(R′2)(R′2), —C(R2)═C(R′2)(R′2), —C≡C—R′2; where R2 is selected from H or an organic functional group (such as C1-12 alkyl, C3-20 cycloalkyl, 3-20 membered heterocyclic group, C6-18 aryl, 5-20 membered heteroaryl, bridged ring group formed by C3-20 cycloalkyl and C3-20 cycloalkyl, bridged ring group formed by C3-20 cycloalkyl and 3-20 membered heterocyclic group, bridged ring group formed by 3-20 membered heterocyclic group and 3-20 membered heterocyclic group); R′2 are the same or different, and independently selected from H or an organic functional group (such as C1-12 alkyl, C3-20 cycloalkyl, 3-20 membered heterocyclic group, C6-18 aryl, 5-20 membered heteroaryl, bridged ring group formed by C3-20 cycloalkyl and C3-20 cycloalkyl, bridged ring group formed by C3-20 cycloalkyl and 3-20 membered heterocyclic group, bridged ring group formed by 3-20 membered heterocyclic group and 3-20 membered heterocyclic group); R3 is selected from H or C1-3 alkyl.
In an embodiment of the present disclosure, one or both of R1 and R′1 include one or two of the following groups as the terminal groups: —O—(C═O)—C(R2)═C(R′2)(R′2), —N(R3)—(C═O)—C(R2)═C(R′2)(R′2), —C(R2)═C(R′2)(R′2), —C≡C—R′2; where R2 is selected from H or C1-6 alkyl (for example, selected from H or C1-3 alkyl; for another example, selected from H or methyl); R′2 are the same or different, and independently selected from H or C1-6 alkyl (for example, selected from H or C1-3 alkyl; for another example, selected from H or methyl); R3 is selected from H or C1-3 alkyl.
In an embodiment of the present disclosure, R and R′ are the same or different, and independently selected from absent, alkylene, where R3 is H or C1-3 alkyl.
In an implementation, R and R′ are the same or different, and independently selected from absent, —CH2—, —CH2CH2—, —NH—, —N(CH3)—, or —N(CH2CH3)—.
In an embodiment of the present disclosure, the polyphenylene ether chain segment has a repeating unit represented by Formula 2:
Specifically, the polyphenylene ether chain segment has a repeating unit represented by Formula 2′:
In an embodiment of the present disclosure, the polyethylene glycol chain segment has a repeating unit represented by Formula 3:
In an embodiment of the present disclosure, the polypropylene glycol chain segment has a repeating unit represented by Formula 4:
In an embodiment of the present disclosure, the polyethanedithiol chain segment has a repeating unit represented by Formula 5:
In an embodiment of the present disclosure, the polycarbonate chain segment has a repeating unit represented by Formula 6:
In an embodiment of the present disclosure, the polysiloxane chain segment has a repeating unit represented by Formula 7:
In an embodiment of the present disclosure, M has a number-average molecular weight of 100-30000.
In an embodiment of the present disclosure, the compound represented by Formula 1 has a number-average molecular weight of 200-30000, in an implementation, the compound represented by Formula 1 has a number-average molecular weight of 300-10000.
In an embodiment of the present disclosure, the compound represented by Formula 1 is selected from at least one of polyethanedithiol acrylate, polyethanedithiol methacrylate, polyethanedithiol diacrylate, polyethanedithiol dimethyl acrylate, polyethanedithiol phenyl ether acrylate, polyethanedithiol monoallyl ether, polyethylene glycol acrylate, polyethylene glycol methacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polyethylene glycol phenyl ether acrylate, polyethylene glycol monoallyl ether, polycarbonate acrylate, polycarbonate methacrylate, polycarbonate diacrylate, polycarbonate dimethyl acrylate, polycarbonate phenyl ether acrylate, polycarbonate monoallyl ether, polypropylene glycol acrylate, polypropylene glycol methacrylate, polypropylene glycol diacrylate, polypropylene glycol dimethacrylate, polypropylene glycol phenyl ether acrylate, polypropylene glycol monoallyl ether, polysiloxane acrylate, polysiloxane methacrylate, polysiloxane diacrylate, polysiloxane dimethyl acrylate, polysiloxane phenyl ether acrylate, and polysiloxane monoallyl ether.
Exemplarily, the auxiliary agent is selected from at least one of the compounds represented by Formulas 1-1, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, and 1-8:
The compound represented by Formula 1-7 is, for example, propargyl-PEG4-acid (CAS: 1415800-32-6); the compound represented by Formula 1-8 is, for example, biotin-PEG4-alkyne (CAS: 1262681-31-1).
In the present disclosure, the auxiliary agent can be prepared using a conventional method in the art or purchased commercially.
In an embodiment of the present disclosure, the negative electrode active material layer includes components with mass percentage contents as following:
Exemplarily, the mass percentage content of the negative electrode active material is 75 wt %, 76 wt %, 77 wt %, 78 wt %, 79 wt %, 80 wt %, 81 wt %, 82 wt %, 83 wt %, 84 wt %, 85 wt %, 86 wt %, 87 wt %, 88 wt %, 89 wt %, 90 wt %, 91 wt %, 92 wt %, 93 wt %, 94 wt %, 95 wt %, 96 wt %, 97 wt %, or 98 wt %.
Exemplarily, the mass percentage content of the conductive agent is 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt %, 10 wt %, 11 wt %, 12 wt %, 13 wt %, 14 wt %, or 15 wt %.
Exemplarily, the mass percentage content of the auxiliary agent is 0.001 wt %, 0.05 wt %, 0.1 wt %, 0.15 wt %, 0.25 wt %, 0.55 wt %, 0.65 wt %, 0.70 wt %, 0.75 wt %, 0.85 wt %, 0.90 wt %, 1.0 wt %, 1.2 wt %, 1.5 wt %, or 2 wt %. When the content of the auxiliary agent is greater than 2 wt %, the excessive content of the auxiliary agent will lead to a decrease of the negative electrode active material, resulting in low capacity of the electrode sheet and poor network for conducting lithium ions and electrons inside the electrode sheet, and thereby, affecting battery performance and failing to meet application conditions. When the content of the auxiliary agent is less than 0.001 wt %, the too low content of the auxiliary agent will lead to a poor forming property, and thus, the structure of the solid electrolyte interphase film on the surface of the negative electrode is unstable, thereby reducing battery performance.
Exemplarily, the mass percentage content of the binder is 0.999 wt %, 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt %, or 10 wt %.
In an embodiment of the present disclosure, the silicon-based material is selected from at least one of nano silicon, SiOx (0<x<2), aluminum-silicon alloy, magnesium-silicon alloy, boron-silicon alloy, phosphorus-silicon alloy, and lithium-silicon alloy.
In an embodiment of the present disclosure, the negative electrode active material further includes a carbon-based material, and the carbon-based material is selected from at least one of artificial graphite, natural graphite, hard carbon, soft carbon, mesocarbon microbead, fullerene, and graphene.
In an embodiment of the present disclosure, the conductive agent is selected from one or more of conductive carbon black, Ketjen black, electroconductive fiber, conductive polymer, acetylene black, carbon nanotube, graphene, flake graphite, conductive oxide, and metal particle.
In an embodiment of the present disclosure, the binder is selected from at least one of polyvinylidene fluoride and its copolymer derivatives, polytetrafluoroethylene and its copolymer derivatives, polyacrylic acid and its copolymer derivatives, polyvinyl alcohol and its copolymer derivatives, polybutadiene styrene rubber and its copolymer derivatives, polyimide and its copolymer derivatives, polyethyleneimine and its copolymer derivatives, polyacrylate and its copolymer derivatives, or carboxymethyl cellulose sodium and its copolymer derivatives.
In an embodiment of the present disclosure, the negative electrode sheet has a surface density of 0.2-15 mg/cm2.
According to the present disclosure, the negative electrode current collector has a thickness of 3 μm-15 μm, in an implementation, the negative electrode current collector has a thickness of 4 μm-10 μm, for example, 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, 12 μm or 15 μm.
According to the present disclosure, the negative electrode active material layer (after rolling) has a thickness of 20 μm-200 μm, in an implementation, the negative electrode active material layer (after rolling) has a thickness of 30 μm-150 μm, for example, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, or 200 μm.
Method for Preparing a Negative Electrode Sheet
The present disclosure further provides a method for preparing a negative electrode sheet, including the following steps:
In an embodiment of the present disclosure, the negative electrode slurry includes 100-600 parts by mass of the solvent, 75-98 parts by mass of the negative electrode active material, 1-15 parts by mass of the conductive agent, 0.001-2 parts by mass of the at least one compound represented by Formula 1, and 0.999-10 parts by mass of the binder.
In an embodiment of the present disclosure, the solvent is selected from at least one of water, acetonitrile, benzene, toluene, xylene, acetone, tetrahydrofuran, hydrofloroether, and N-methylpyrrolidone.
In an embodiment of the present disclosure, the negative electrode slurry is a negative electrode slurry that has been subjected to sieving, for example, with a 200-mesh sieve.
In an embodiment of the present disclosure, the temperature of drying treatment is 50° C.-110° C., and the time of drying treatment is 6-36 h.
Lithium-Ion Battery
The present disclosure further provides a lithium-ion battery including the above negative electrode sheet.
The following will provide a further detailed description of the present disclosure in conjunction with specific embodiments. It should be understood that the following embodiments are only illustrative illustrations and explanations of the present disclosure, and should not be interpreted as limiting the protection scope of the present disclosure. All technologies implemented based on the above content of the present disclosure fall within the scope intended to be protected by the present disclosure.
The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples can be obtained commercially unless otherwise specified.
1) Preparation of a Positive Electrode Sheet:
95 g of a positive electrode active material (nickel-cobalt-manganese ternary material (NCM811)), 2 g of a binder (polyvinylidene fluoride (PVDF)), 2 g of a conductive agent (conductive carbon black), and 1 g of the conductive agent (carbon nanotube) are mixed, 400 g of N-methylpyrrolidone (NMP) is added, they are stirred under a vacuum mixer until the mixed system forms a positive electrode slurry that is uniform and flowable. The positive electrode slurry is coated uniformly on an aluminum foil with a thickness of 12 μm, and after drying at 100° C. for 36 h and vacuum treating, an electrode sheet is obtained, and the electrode sheet is subjected to rolling and cutting to obtain the positive electrode sheet.
2) Preparation of a Negative Electrode Sheet:
75 g of silicon monoxide, 5 g of a conductive agent (single-walled carbon nanotube (SWCNT)), 10 g of the conductive agent (conductive carbon black (Super P Conductive Carbon Black)), 2 g of polyethylene glycol methyl methacrylate, 4 g of a binder (carboxymethylcellulose sodium (CMC)), 4 g of the binder (styrene butadiene rubber (SBR)), and 500 g of deionized water are prepared into a slurry using a wet process, the slurry is coated on a surface of a copper foil of a negative electrode current collector, and after drying, rolling and die-cutting, the negative electrode sheet is obtained.
3) Preparation of an Electrolyzing Solution:
ethylene carbonate, propylene carbonate, diethyl carbonate and n-propyl propionate are uniformly mixed in a proportion of 20:10:15:55 by mass ratio in a glove box which is filled with argon gas and in which the oxygen content in water is qualified, then 1 mol/L of fully dried lithium hexafluorophosphate (LiPF6) is quickly added thereto, they are stirred uniformly to prepare the electrolyzing solution.
4) Preparation of a Lithium-Ion Battery
a lithium-ion battery cell is prepared by the obtained positive electrode sheet, negative electrode sheet, and a separating membrane, and is subjected to liquid injection and encapsulation, and welding to obtain the lithium-ion battery.
Example 1 is referred to for the specific process of the Comparative Example 1.1, the main difference is that poly (polyethylene glycol methyl methacrylate) with the same mass as the polyethylene glycol methyl methacrylate monomer is used in Comparative Example 1.1. Polyethylene glycol methyl methacrylate and azodiisobutyronitrile, which have the same masses, are used for poly (polyethylene glycol methyl methacrylate), and are fully polymerized at 60° C., after polymerization, the polymer is added to Comparative Example 1.1 after C═C double bond peak cannot be detected in the polymer by infrared detection, other conditions are the same as Example 1.
Example 1 is referred to for the specific process of Comparative Example 1.2, and the main difference is that the polyethylene glycol methyl methacrylate monomer is not added in Comparative Example 1.2, and other conditions are the same as Example 1.
Example 1 is referred to for the specific processes of Examples 2-6 and other Comparative Examples, the main differences lie in process conditions for the negative electrode sheet, addition amounts of respective components, and types of respective component materials. Specific details are shown in Tables 1 and 2.
The performance test is performed on the batteries prepared by the above Examples and Comparative Examples.
(1) AC Impedance-based Battery Internal Resistance Test Method: Metrohm PGSTAT302N Chemical Workstation is used, the AC impedance test is conducted on a 50% SOC lithium-ion battery in the range of 100 KHz-0.1 mHz at 25° C., the results of the test are listed in Table 3.
The results of the internal resistance test during the battery cycling process indicate that the lithium-ion batteries prepared by the Examples of the present disclosure have an internal resistance smaller than that of the lithium-ion batteries prepared by the Comparative Examples. The main reason is that the auxiliary agent added in the present disclosure can form a solid electrolyte interphase film on the surface of the silicon-based material. The solid electrolyte interphase film is different from solid electrolyte interphase films on surfaces of conventional silicon-based materials, and has the functional characteristics that the polymer component has a high content and high molecular weight, and conducts lithium-ions in a high speed, and so on, therefore, lithium-ions can be quickly conducted to pass through, and the prepared lithium-ion battery has a lower internal resistance, at the same time, the increase of internal resistance of the lithium-ion battery is small during cycling, and thus, it has a good application prospect.
(2) Battery cycling performance test method: lithium-ion batteries are subjected to a charging and discharging cycling test on a blue battery charging and discharging test cabinet under the test conditions of 25° C., 0.5 C/0.5 C charging and discharging, and the results of the test are listed in Table 4.
The results of the cycling performance test for the above Examples and Comparative Examples indicate that the lithium-ion batteries prepared by the Examples of the present disclosure have a capacity retention rate higher than that of the lithium-ion batteries prepared by the Comparative Examples during the cycling process. The main reason is that the auxiliary agent added in the present disclosure can form a solid electrolyte interphase film on the surface of the silicon-based material. The solid electrolyte interphase film is different from solid electrolyte interphase films on surfaces of conventional silicon-based materials, and has the functional characteristics that the polymer component has a high content and high molecular weight, and conducts lithium-ions in a high speed, and so on. For a solid electrolyte interphase film of a conventional silicon-based material, along with the alloying and dealloying of lithium-ions in the battery cycling process, irregular volume expansion appears on the surface of the silicon-based material, thus, more new interphases are generated, and the new interphases consume electrolyzing solution and lithium salt, and the solid electrolyte interphase film continues to form, thereby reducing battery performance. In the present disclosure, due to the addition of the auxiliary agent, a more stable solid electrolyte interphase film with higher property of conducting lithium-ions can be formed on the surface of the silicon-based material, thereby greatly improving the performance of the silicon-based negative electrode.
The results of the cycling charging and discharging performance test for the above Examples and Comparative Examples indicate that the silicon-based material negative electrode sheet prepared by the present disclosure has a low internal resistance during the cycling process, and there are good channels in the silicon-based material negative electrode sheet for conducting lithium-ions and electrons, and thus, the prepared lithium-ion battery has good cycling performance.
1) Preparation of a Positive Electrode Sheet:
95 g of a positive electrode active material (lithium cobalt oxide), 2 g of a binder (polyvinylidene fluoride (PVDF)), 2 g of a conductive agent (conductive carbon black), and 1 g of the conductive agent (carbon nanotube) are mixed, 400 g of N-methylpyrrolidone (NMP) is added, and they are stirred under a vacuum mixer until the mixed system forms a positive electrode slurry that is uniform and flowable. The positive electrode slurry is coated uniformly on an aluminum foil with a thickness of 12 μm, and after drying at 100° C. for 36 h and vacuum treating, an electrode sheet is obtained, then the electrode sheet is subjected to rolling and cutting to obtain the positive electrode sheet.
2) Preparation of a Negative Electrode Sheet:
25 g of silicon monoxide, 50 g of graphite, 5 g of a conductive agent (single-walled carbon nanotube (SWCNT)), 10 g of the conductive agent (conductive carbon black (Super P Conductive Carbon Black)), 2 g of polyethylene glycol methyl methacrylate, 4 g of a binder (carboxymethylcellulose sodium (CMC)), 4 g of the binder (styrene butadiene rubber (SBR)), and 500 g of deionized water are prepared into a slurry using a wet process, the slurry is coated on a surface of a copper foil of a negative electrode current collector, and after drying, rolling, and die-cutting, the negative electrode sheet is obtained.
3) Preparation of an Electrolyzing Solution:
ethylene carbonate, propylene carbonate, diethyl carbonate and n-propyl propionate are uniformly mixed in a proportion of 20:10:15:55 by mass ratio in a glove box which is filled with argon gas and in which the oxygen content in water is qualified, then 1 mol/L of fully dried lithium hexafluorophosphate (LiPF6) is quickly added thereto, they are stirred uniformly to prepare the electrolyzing solution.
4) Preparation of a Lithium-Ion Battery
a lithium-ion battery cell is prepared by the obtained positive electrode sheet, negative electrode sheet, and a separating membrane (a polyethylene separating membrane), and is subjected to liquid injection and encapsulation, and welding to obtain the lithium-ion battery.
Example 7 is referred to for the specific process of the Comparative Example 7.1, the main difference is that poly (polyethylene glycol methyl methacrylate) with the same mass as the polyethylene glycol methyl methacrylate monomer is used in Comparative Example 7.1. Polyethylene glycol methyl methacrylate and azodiisobutyronitrile, which have the same masses, are used for poly (polyethylene glycol methyl methacrylate), and are fully polymerized at 60° C., after polymerization, the polymer is added to Comparative Example 7.1 after C═C double bond peak cannot be detected in the polymer by infrared detection, other conditions are the same as Example 7.
Example 7 is referred to for the specific process of Comparative Example 7.2, and the main difference is that the polyethylene glycol methyl methacrylate monomer is not added in Comparative Example 7.2, and other conditions are the same as Example 7.
Example 7 is referred to for the specific processes of Examples 8-12 and other Comparative Examples, the main differences lie in process conditions for the negative electrode sheet, addition amounts of respective components, and types of respective component materials. Specific details are shown in Tables 5 and 6.
The performance test is performed on the batteries prepared by the above Examples and Comparative Examples:
(3) AC Impedance-based Battery Internal Resistance Test Method: Metrohm PGSTAT302N Chemical Workstation is used, the AC impedance test is conducted on a 50% SOC lithium-ion battery in the range of 100 KHz-0.1 mHz at 25° C., the results of the test are listed in Table 7.
The results of the internal resistance test during the battery cycling process indicate that the lithium-ion batteries prepared by the Examples of the present disclosure have an internal resistance smaller than that of the lithium-ion batteries prepared by the Comparative Examples. The main reason is that the auxiliary agent added in the present disclosure can form a solid electrolyte interphase film on the surface of the silicon-based material. The solid electrolyte interphase film is different from solid electrolyte interphase films on surfaces of conventional silicon-based materials, and has the functional characteristics that the polymer component has a high content and high molecular weight, and conducts lithium-ions in a high speed, and so on, therefore, lithium-ions can be quickly conducted to pass through, and the prepared lithium-ion battery has a lower internal resistance, at the same time, the increase of internal resistance of the lithium-ion battery is small during cycling, and thus, it has a good application prospect.
(4) Battery cycling performance test method: lithium-ion batteries are subjected to a charging and discharging cycling test on a blue battery charging and discharging test cabinet under the test conditions of 25° C., 0.5 C/0.5 C charging and discharging, and the results of the test are listed in Table 8.
The results of the cycling performance test for the above Examples and Comparative Examples indicate that the lithium-ion batteries prepared by the Examples of the present disclosure have a capacity retention rate higher than that of the lithium-ion batteries prepared by the Comparative Examples during the cycling process. The main reason is that the auxiliary agent added in the present disclosure can form a solid electrolyte interphase film on the surface of the silicon-based material. The solid electrolyte interphase film is different from solid electrolyte interphase films on surfaces of conventional silicon-based materials, and has the functional characteristics that the polymer component has a high content and high molecular weight, and conducts lithium-ions in a high speed, and so on. For a solid electrolyte interphase film of a conventional negative electrode active material, along with the alloying and dealloying of lithium-ions in the battery cycling process, irregular volume expansion appears on the surface of the negative electrode active material, thus, more new interphases are generated, and the new interphases consume electrolyzing solution and lithium salt, and the solid electrolyte interphase film continues to form, thereby reducing battery performance. In the present disclosure, due to the addition of the auxiliary agent, a more stable solid electrolyte interphase film with higher property of conducting lithium-ions can be formed on the surface of the negative electrode active material, thereby greatly improving the performance of the silicon-based negative electrode.
The results of the cycling charging and discharging performance test for the above Examples and Comparative Examples indicate that the negative electrode sheet prepared by the present disclosure has a low internal resistance during the cycling process, and there are good channels in the negative electrode sheet for conducting lithium-ions and electrons, and thus, the prepared lithium-ion battery has good cycling performance.
The above describes the embodiments of the present disclosure. However, the present disclosure is not limited to the aforementioned embodiments. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure shall be included within the protection scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021102765737 | Mar 2021 | CN | national |
This application is a continuation of International Application No. PCT/CN2022/081032, filed on Mar. 15, 2022, which claims priority to Chinese Patent Application No. 202110276573.7, filed on Mar. 15, 2021, both of which are hereby incorporated by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2022/081032 | Mar 2022 | US |
| Child | 18227252 | US |
