Lithium ion battery and electric device
By using a synergistic protective layer formed by fluorinated phosphazene compounds and boron compounds in lithium-ion batteries, the problems of oxidation decomposition and high-temperature corrosion of oxide solid electrolytes under high voltage were solved, and the high and low temperature performance and stability of the batteries were optimized.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-10
- Publication Date
- 2026-03-24
AI Technical Summary
Oxide solid electrolytes are prone to oxidation and decomposition under high voltage at the positive electrode of lithium-ion batteries, leading to interfacial side reactions and impedance growth, as well as cycle capacity decay and performance degradation under high temperature conditions.
In lithium-ion batteries, fluorinated phosphazene compounds and boron compounds are used as additives to form an electron blocking layer and a chemical scavenging layer, which synergistically suppress the interfacial corrosion of oxide solid electrolytes and optimize high and low temperature performance.
It improves the stability of oxide solid electrolytes under high voltage, enhances high-temperature and low-temperature cycling performance, balances high and low temperature storage performance, and strengthens interface stability and ionic conductivity.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of battery, in particular to a lithium ion battery and an electric device. BACKGROUND
[0002] Lithium ion batteries have become the mainstream energy storage devices in the fields of consumer electronic devices and new energy vehicles due to their core advantages of high energy density, low self-discharge rate and long cycle life, and their stable operation relies on the synergistic effect of the positive electrode, negative electrode, electrolyte and separator. However, in practical applications, the positive electrode material is prone to structural distortion, frequent interface side reactions and intensified risk of thermal runaway, and the current industry mainly improves or alleviates the above problems by means of doping modification, building core-shell structure and optimizing electrolyte composition.
[0003] Research has found that the oxide solid electrolyte used in the positive electrode layer can build excellent ion channels and greatly improve the rate performance of the battery, especially for fast charging applications. However, it is prone to oxidative decomposition at high voltage (4.55V), which causes serious interface side reactions and impedance rise, especially the capacity decay and performance deterioration under high temperature conditions. SUMMARY In view of the problems in the prior art that the oxide solid electrolyte applied to the positive electrode of the lithium ion battery causes interface side reactions and impedance growth due to its poor oxidation resistance at high voltage, and the cycle capacity decay and storage performance deterioration under high temperature conditions, a lithium ion battery and an electric device are provided.
[0005] The technical solution adopted by the present application to solve the above technical problems is as follows: On the one hand, the present application provides a lithium ion battery, comprising a positive electrode, a negative electrode and an electrolyte, the positive electrode comprising a positive electrode active material layer, the positive electrode active material layer comprising a positive electrode active material and an oxide solid electrolyte, the electrolyte comprising a solvent, a lithium salt, a first additive and a second additive, the first additive comprising a fluorine-containing phosphazene compound, and the second additive comprising a boron-based compound; The lithium ion battery satisfies the following conditions: Formula 1: 0.23≤(A+B) / X≤22, 0.08≤A / B≤4, and 0.1≤A≤2, 0.25≤B≤2.5, 0.1≤X≤3; Wherein, A% is the mass percentage content of the first additive in the electrolyte; B% is the mass percentage content of the second additive in the electrolyte; X% is the mass percentage content of the oxide solid electrolyte in the positive electrode active layer.
[0006] Optionally, the lithium ion battery satisfies the following conditions: Formula 2: 0.28≤(A+B) / X≤21.25.
[0007] Optionally, the first additive and the second additive satisfy the following conditions: Formula 3: 0.09≤A / B≤3.27.
[0008] Optionally, the lithium ion battery satisfies at least one of the following conditions: (1) 0.6≤A≤2; (2) 0.5≤B≤2.4; (3) 0.5≤X≤2.
[0009] Optionally, the first additive comprises at least one of the following fluorine-containing phosphazene compounds: .
[0010] Optionally, the second additive comprises one or more of lithium tetrafluoroborate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate.
[0011] Optionally, the oxide solid-state electrolyte comprises one or more of lithium titanium aluminum phosphate, lithium lanthanum zirconate, lithium aluminum germanium phosphate, lithium lanthanum titanate, and lithium titanium phosphate.
[0012] Optionally, the positive electrode active material comprises a transition metal lithium oxide; the chemical formula of the transition metal lithium oxide is Li 1+x Ni y Co z M (1-y-z) O2, wherein -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; wherein M is selected from one or more of Mg, Zn, Ga, Ba, Al, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, Zr.
[0013] Optionally, the solvent comprises at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, propyl acetate, ethyl butyrate, propyl propionate, γ-butyrolactone, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.
[0014] In another aspect, the present application provides an electrical device comprising the lithium ion battery.
[0015] The present application has the following beneficial effects: The lithium-ion battery provided in this application includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode active material layer includes a positive electrode active material and an oxide solid electrolyte. The electrolyte includes a first additive and a second additive. In the lithium-ion battery, when the two additives are used together, the first additive (a fluorophosphazene compound) preferentially adsorbs onto the surface of the oxide solid electrolyte with its P and N lone pair electrons, forming an electron blocking layer. Its fluorine atoms further enhance the density and chemical inertness of the interface barrier. The second additive (a boron compound) complexes acidic species through the empty orbitals of boron atoms, forming a chemical scavenging layer, which together block electron leakage and acid erosion pathways. In addition, the first additive... The fluorine atoms in the additive synergistically capture HF with the PN structure, reducing interfacial corrosion of the oxide solid electrolyte. The boron-based components further remove residual PF5 / HF, jointly suppressing high-temperature side reactions. The interfacial stability is significantly better than that of a single additive. The high ionic conductivity of the boron-based interfacial film of the second additive can compensate for the ion migration barrier caused by the fluorinated phosphazene compounds of the first additive, alleviating the limitation on the kinetics of lithium-ion batteries at low temperatures. At the same time, the first additive can inhibit the excessive growth of the boron-based interfacial film of the second additive, so that the high and low temperature performance is well balanced. When the first and second additives are used together, the high-temperature cycling, low-temperature cycling and high-temperature storage performance are improved.
[0016] Furthermore, by controlling the mass percentage of the first additive A, the second additive B, and the oxide solid electrolyte X in the positive electrode active material, this application satisfies the following relationships: 0.23≤(A+B) / X≤22, 0.08≤A / B≤4, and 0.1≤A≤2, 0.25≤B≤2.5, 0.1≤X≤3. This allows for the improvement of the oxide solid electrolyte's ionic conductivity on the positive electrode while simultaneously enhancing the stability of the oxide solid electrolyte under high voltage, thereby better leveraging its synergistic effect and optimizing performance. Detailed Implementation
[0017] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0018] This invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises a positive electrode active material layer, which comprises a positive electrode active material and an oxide solid electrolyte. The electrolyte comprises a solvent, a lithium salt, a first additive, and a second additive. The first additive comprises a fluorinated phosphazene compound, and the second additive comprises a boron compound. The lithium-ion battery meets the following conditions: Equation 1: 0.23≤(A+B) / X≤22, 0.08≤A / B≤4, and 0.1≤A≤2, 0.25≤B≤2.5, 0.1≤X≤3; Wherein, A% is the mass percentage content of the first additive in the electrolyte; B% is the mass percentage of the second additive in the electrolyte; X% represents the mass percentage of the oxide solid electrolyte in the positive electrode active layer.
[0019] It should be noted that the first additive (fluorinated phosphazene compound) undergoes electrochemical polymerization at the positive electrode interface to form an interfacial protective layer rich in P, N, and F elements. Specifically, the P and N atoms in its phosphazene structure both have lone pairs of electrons, which can adsorb and coordinate with Lewis acid sites located on the surface of the oxide solid electrolyte to form an electronic insulating layer, effectively inhibiting interfacial electron migration and the reduction of high-valence metal ions, and significantly improving high-temperature cycling stability. The PN polar bond can capture hydrofluoric acid (HF), while the introduced fluorine atoms further enhance the protonicity and chemical stability of the interfacial layer, synergistically reducing the corrosion of the solid electrolyte and inhibiting the dissolution of transition metals at high temperatures. The high electronegativity of fluorine can enhance the bond energy of the interfacial layer and optimize the interfacial electric field distribution, jointly constructing a more stable barrier structure with the phosphazene functional groups, but it also increases the resistance to interfacial ion migration to some extent, resulting in a slight decrease in capacity at low temperatures. Since there is no current during storage, the high-temperature storage performance does not change significantly.
[0020] The second additive (boron-based compound) undergoes oxidative decomposition at the positive electrode interface to form an interfacial film containing BO components. The empty p orbitals of its B atoms can strongly complex free PF5 and HF in the electrolyte, inhibiting their corrosion of the solid electrolyte and significantly reducing gas generation and interfacial impedance growth, thus improving high-temperature storage performance. The lithium borate components in the decomposition products have high lithium-ion conductivity, and the B atoms, as weak Lewis acid sites, can interact with lithium ions, promoting Li-ion exchange. + The desolvation process helps improve high-temperature cycling performance; the formed interfacial film has a certain thickness, and component B has a positive effect on Li. + There are strong interactions, which increase the ion migration barrier at low temperatures, resulting in a slight decrease in performance.
[0021] Specifically, the electrolyte contains both fluorinated phosphazene compounds and boron compounds. The former forms a stable interfacial film through the synergistic effect of the fluorinated groups and the phosphazene structure, while the latter captures active substances in the electrolyte through the electron-deficient characteristics of boron. Together, they suppress side reactions between the solid electrolyte and the electrolyte. Furthermore, by controlling the mass percentage of the first additive A, the second additive B, and the oxide solid electrolyte X in the positive electrode active material, this application satisfies the following relationships: 0.23≤(A+B) / X≤22, 0.08≤A / B≤4, and 0.1≤A≤2, 0.25≤B≤2.5, 0.1≤X≤3. This allows for the improvement of the oxide solid electrolyte's ionic conductivity on the positive electrode while simultaneously enhancing the stability of the oxide solid electrolyte under high voltage, thereby better leveraging its synergistic effect and optimizing performance. Previous verification revealed that when (A+B) / X < 0.23, the interfacial protective layer was incomplete, resulting in insufficient electronic insulation and an inability to effectively suppress the reduction of high-valence metal ions and HF corrosion in the oxide electrolyte, leading to a significant decrease in high-temperature cycling and storage stability. When (A+B) / X > 22, excessive additive decomposition products accumulated excessively, blocking ion migration channels and causing a significant increase in interfacial impedance, especially with a sharp capacity decay under low-temperature conditions. Therefore, by limiting the range of the (A+B) / X ratio, the synergistic relationship between the total amount of additives and the content of solid electrolyte can be controlled, ensuring both the suppression effect on interfacial reactions and avoiding the impact of excessive additives on the ionic conductivity of the electrolyte. If A / B < 0.08, the fluorophosphazene additives are relatively insufficient, resulting in a discontinuous electron barrier layer formed at the interface, which cannot effectively suppress electron migration and Ti. 4+ Plasma reduction, while boron-based lithium salts cannot be effectively anchored, reduces the ability to remove acidic species at the interface; if A / B > 4, the content of boron-based lithium salts is relatively insufficient, the complexation ability of empty B orbitals for PF5 and HF is weakened, the interfacial side reactions are aggravated during high-temperature storage, gas production and impedance increase significantly, and the synergistic protection mechanism fails. This application ensures the synergistic ratio of the two types of additives by limiting the range of A / B ratio. Fluorophosphazene compounds focus on interfacial film formation protection, while boron-based compounds focus on side reaction inhibition, and the two complement each other. Further verification revealed that when the content of the first additive A% was below 0.1%, the interfacial polymerization layer was incomplete, resulting in insufficient electron blocking and HF capture effects. When it was above 2%, the excessively thick interfacial layer hindered ion migration, leading to deterioration in low-temperature performance. When the content of the second additive B% was below 0.25%, the ability to remove acidic species was insufficient, exacerbating interfacial corrosion. When it was above 2.5%, the excessive boron-containing interfacial film thickened, limiting lithium-ion transport kinetics. When the content of the oxide solid electrolyte X% was below 0.1%, the ion conduction pathway was insufficient, affecting fast-charging performance. When it was above 3%, the specific surface area was too large, and the additive could not achieve effective interfacial coverage, resulting in a decrease in protection. Therefore, this application limits the range of A%, B%, and X% to avoid insufficient interfacial protection or electrolyte performance degradation caused by excessively high or low levels of a single component, ultimately achieving a balance between improved stability of the solid electrolyte under high voltage and fast-charging performance.
[0022] Further, the mass percentage A% of the first additive in the electrolyte can be 0.1%, 0.2%, 0.22%, 0.24%, 0.4%, 0.6%, 1%, 1.2%, 1.4%, 1.8%, or 2%. The mass percentage (B%) of the second additive in the electrolyte can be 0.25%, 0.5%, 0.55%, 0.6%, 1.5%, 2%, 2.2%, 2.4%, 2.45%, or 2.5%. The mass percentage (X%) of the oxide solid electrolyte in the positive electrode active layer is 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, and 3%.
[0023] In some embodiments, the lithium-ion battery satisfies the following conditions: Equation 2: 0.28≤(A+B) / X≤21.25.
[0024] Specifically, the lower limit of the ratio (A+B) / X in Equation 2 is 0.28 to ensure that the additive content is sufficient to suppress the oxidative decomposition of solid electrolyte under high voltage and reduce the accumulation of interfacial side reaction products. The upper limit of 21.25 avoids excessive additives from damaging the ion channels constructed by the solid electrolyte, thus preventing ion transport obstruction. This ratio range, through precise control of the ratio of additives to solid electrolyte, alleviates the problem of insufficient electrolyte interface stability while maintaining the ionic conductivity of the positive electrode active layer, thereby improving battery capacity retention and cycle life under high temperature and high voltage conditions.
[0025] In some embodiments, the first additive and the second additive satisfy the following conditions: Equation 3: 0.09≤A / B≤3.27.
[0026] Specifically, by limiting the mass ratio range of fluorinated phosphazene compounds to boron-based compounds, the synergistic effect of the two types of additives in the electrolyte is achieved. When the A / B ratio is below 0.09, an excess of boron-based compounds leads to insufficient protection of the positive electrode interface by the fluorinated phosphazene compounds, failing to effectively inhibit the high-voltage oxidative decomposition of the oxide solid electrolyte. When the A / B ratio is above 3.27, an excess of fluorinated phosphazene compounds weakens the dissociation-promoting effect of boron-based compounds on lithium salts, resulting in obstructed interfacial ion transport. By controlling the A / B ratio within the range of 0.09-3.27, the ability of fluorinated phosphazene compounds to form a stable fluorinated layer on the positive electrode surface is ensured, while maintaining the characteristic of boron-based compounds to optimize lithium ion migration rate. The two work synergistically to reduce the interfacial impedance between the positive electrode active layer and the electrolyte under high voltage, while simultaneously inhibiting the structural degradation of the oxide solid electrolyte during cycling.
[0027] In some embodiments, the lithium-ion battery satisfies at least one of the following conditions: (1) 0.6≤A≤2; (2) 0.5 ≤ B ≤ 2.4; (3) 0.5≤X≤2.
[0028] Specifically, by limiting the content range of the first additive, the second additive, and the oxide solid electrolyte, the interfacial stability and electrochemical performance between the electrolyte and the positive electrode active layer are synergistically optimized; more specifically, limiting the mass percentage content range of the first additive (0.6≤A≤2) ensures that the fluorinated phosphazene compound forms a stable interfacial film in the electrolyte, suppressing side reactions and reducing impedance; Limiting the mass percentage range of the second additive (0.5≤B≤2.4) allows the boron-based compounds to effectively passivate the electrode surface and reduce electrolyte decomposition at high temperatures; Limiting the mass percentage range of oxide solid electrolyte in the positive electrode active layer (0.5≤X≤2) balances ion conduction efficiency and material structure stability, and avoids excessive solid electrolyte leading to deterioration of interface contact. The synergistic effect of these three factors can alleviate capacity decay and performance degradation under high voltage and high temperature conditions.
[0029] In some embodiments, the first additive includes at least one of the following fluorophosphazene compounds: .
[0030] Specifically, this application specifies that the first additive is a fluorinated phosphazene compound. The fluorine element in the fluorinated phosphazene compound has strong electronegativity and can preferentially form a dense and stable passivation film on the positive electrode surface, inhibiting the oxidation reaction between the oxide solid electrolyte and the electrolyte under high voltage. At the same time, the phosphazene skeleton structure has high thermal stability and oxidation resistance, which can reduce the occurrence of interfacial side reactions under high temperature conditions. That is, when the first additive is any one or more of the above-mentioned compounds, it can work synergistically with the boron-based compounds of the second additive to further optimize the electrode-electrolyte interface compatibility, reduce the interface impedance, and thus improve the high-temperature cycle performance and fast charging capability of the battery.
[0031] In some embodiments, one or more of lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), and lithium dioxalate borate (LiBOB) are used.
[0032] Specifically, by limiting the second additive to a specific boron-based compound, the stability of the cathode interface under high voltage is synergistically addressed. Lithium tetrafluoroborate has excellent film-forming ability, forming a stable interfacial film on the cathode surface and suppressing side reactions between the oxide solid electrolyte and the electrolyte. Lithium difluorooxalate borate preferentially participates in the oxidation reaction, forming a uniform passivation layer on the cathode surface, reducing interfacial impedance and improving lithium-ion migration efficiency. Lithium dioxalate borate stabilizes free metal ions in the electrolyte through its strong coordination effect, reducing structural degradation caused by the dissolution of transition metals in the cathode material. The selection of the above boron-based compounds not only specifically suppresses the occurrence of interfacial side reactions under high voltage, but also complements each other through different mechanisms of action, maintaining the interfacial stability between the cathode active layer and the electrolyte under high temperature conditions.
[0033] In some embodiments, the oxide solid electrolyte includes lithium aluminum titanium phosphate (LATP), lithium lanthanum zirconate (LLZO), lithium aluminum germanium phosphate (LAGP), lithium lanthanum titanate (LLTO), and lithium titanium phosphate (LTTP).
[0034] Specifically, the lithium titanium aluminum phosphate possesses three-dimensional ion channels and a titanium-aluminum synergistic effect, which can suppress lattice oxygen escape under high voltage; the lanthanide coordination structure of lithium lanthanum zirconate can enhance oxidation potential and reduce the risk of electrolyte decomposition; the germanium doping of lithium germanium aluminum phosphate can increase the high-temperature phase transition temperature and reduce the tendency for thermal runaway; the layered structure of lithium lanthanum titanate is conducive to rapid lithium ion migration and reduces interfacial impedance; the olivine-type structure of lithium titanium phosphate has excellent thermodynamic stability; the above-mentioned oxide solid electrolytes work synergistically on the positive electrode active layer through different stabilization mechanisms, effectively suppressing material decomposition and interfacial side reactions under high voltage conditions while maintaining ion conduction performance.
[0035] In some embodiments, the positive electrode active material comprises a transition metal lithium oxide; the chemical formula of the transition metal lithium oxide is Li. 1+x Ni y Co z M (1-y-z) O2, where -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; M is selected from one or more of Mg, Zn, Ga, Ba, Al, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.
[0036] Specifically, the positive electrode active material can be one or more of the above-mentioned materials.
[0037] In some embodiments, the positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including a positive active substance.
[0038] In this application, there is no particular limitation on the type of positive electrode current collector; it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper. In one embodiment, the positive electrode current collector is a metallic material.
[0039] In some embodiments, the positive electrode active material layer further includes a positive electrode conductive agent, a positive electrode binder, and a solvent.
[0040] In some embodiments, the type of positive conductive agent mentioned in this invention is not limited, and any known conductive agent can be used.
[0041] In some embodiments, the positive electrode conductive agent mentioned in this invention includes at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene.
[0042] In one embodiment, the type of positive electrode binder mentioned in this invention is not limited, and any known positive electrode binder can be used.
[0043] In some embodiments, the positive electrode binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose.
[0044] The negative electrode active materials include natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 At least one of Li-Al alloys.
[0045] In this invention, there are no particular limitations on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector, etc.
[0046] In some preferred embodiments, the negative current collector comprises copper foil.
[0047] In some embodiments, the negative electrode further includes a negative electrode active material layer disposed on at least one side surface of the current collector, and the negative electrode active material layer further includes a negative electrode conductive agent, a negative electrode binder, a thickener, and a solvent.
[0048] The negative electrode conductive agent includes at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene. The negative electrode binder includes styrene-butadiene latex, and the thickener includes CMC. The solvent includes deionized water. In the lithium-ion battery mentioned in this application, a separator is usually provided between the positive and negative electrodes to prevent short circuits. There are no particular restrictions on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application.
[0049] In some embodiments, the diaphragm includes a porous sheet-like or non-woven material with excellent liquid retention properties. The diaphragm includes resin or glass fiber diaphragm materials, including but not limited to polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc.
[0050] In some embodiments, the lithium-ion battery may include an outer packaging that can be used to encapsulate the electrode assembly and electrolyte described above.
[0051] In some implementations, the outer packaging of a lithium-ion battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of a lithium-ion battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.
[0052] This application does not impose any particular restrictions on the shape of the lithium-ion battery; it can be cylindrical, square, or any other arbitrary shape.
[0053] In some embodiments, the solvent includes at least one selected from ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, propyl acetate, ethyl butyrate, propyl propionate, γ-butyrolactone, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.
[0054] In some embodiments, the electrolyte further includes a lithium salt.
[0055] Lithium salts are existing technology and are not limited in this application. For example, lithium salts can be at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium perchlorate, and lithium difluorophosphate.
[0056] It should be noted that this application does not impose any particular limitation on the preparation method of the electrolyte. Those skilled in the art can prepare the electrolyte using conventional technical means, such as mixing the raw materials evenly according to the specified ratio.
[0057] Specifically, the aforementioned solvents can dissolve the first additive, the second additive, and the lithium salt.
[0058] In another embodiment, the present invention provides an electrical device including the aforementioned lithium-ion battery.
[0059] The aforementioned electrical devices may include, but are not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
[0060] The present invention will be further illustrated by the following examples.
[0061] Table 1 Example 1 This embodiment illustrates the lithium-ion battery disclosed in this invention, and includes the following operational steps: Preparation of positive electrode Lithium cobalt oxide (CCO), a positive electrode active material, acetylene black (SuperP), a positive electrode conductive agent, and polyvinylidene fluoride (PVDF) binder were mixed uniformly at a mass ratio of 97:1.5:1.5 and then uniformly dispersed with 1-methyl-2-pyrrolidone (NMP) to form a uniform positive electrode slurry 1. 1% (by mass, representing 1% of the total amount of lithium cobalt oxide, acetylene black (SuperP), and PVDF binder) of LATP oxidized solid electrolyte was uniformly dispersed in positive electrode slurry 1 to obtain positive electrode slurry 2. The mixed positive electrode slurry 2 was coated on both sides of an aluminum foil current collector, and then baked, rolled, and cut into sheets to obtain the positive electrode.
[0062] Preparation of negative electrode The negative electrode active material artificial graphite, negative electrode conductive agent acetylene black (Super P), thickener CMC and negative electrode binder SBR are mixed evenly in a mass ratio of 94:2:1.2:2.8 and then evenly dispersed with deionized water to form a uniform negative electrode slurry. The mixed slurry is coated on both sides of the copper foil current collector, and then baked, rolled, and cut into sheets to obtain the negative electrode.
[0063] Preparation of electrolyte a. Mix ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (EP), and diethyl carbonate (DEC) in a mass ratio of 10:20:40:30 to form a mixed solvent. Remove water using a molecular sieve and set aside. Add 1M LiPF6 and mix thoroughly. b. Add additives (the types and amounts of additives are shown in Table 1) to the colorless and transparent liquid obtained in step a to obtain the electrolyte.
[0064] Manufacturing of lithium-ion batteries The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode sheets. After winding and welding the tabs, a bare cell is obtained. The bare cell is then placed in an aluminum-plastic film for electrolyte injection and encapsulation to obtain a lithium-ion battery.
[0065] Example 2-32 Examples 2-32 are used to illustrate the lithium-ion battery disclosed in this invention, including most of the operations in Example 1. The difference is that the type of the first additive, the mass percentage A / % of the first additive in the electrolyte, the type of the second additive, the mass percentage B / % of the second additive in the electrolyte, the type of oxide solid electrolyte, and the content X / % of the oxide solid electrolyte in the positive electrode active layer in Examples 2-32 are all based on Table 1.
[0066] Comparative Examples 1-27 Comparative Examples 1-27 are used to illustrate the lithium-ion battery disclosed in this invention, including most of the operations in Example 1. The difference is that the type of the first additive, the mass percentage A / % of the first additive in the electrolyte, the type of the second additive, the mass percentage B / % of the second additive in the electrolyte, the type of oxide solid electrolyte, and the content X / % of the oxide solid electrolyte in the positive electrode active layer in Comparative Examples 1-27 are all based on Table 1.
[0067] Performance testing The following performance tests were performed on Examples 1-32 and Comparative Examples 1-27 prepared above: 60℃ Storage Performance Test The lithium-ion batteries prepared in the above embodiments and comparative examples were charged at 25°C at a rate of 1C to the cutoff voltage, with a cutoff current of 0.025C, and left to stand for 5 minutes. The thickness H1 of the lithium-ion battery was then measured. After that, the batteries were stored at 60°C for 60 days, and the thickness H2 of the lithium-ion battery was measured after the storage period.
[0068] Thickness expansion rate = [(H2-H1) / H1]×100%.
[0069] 45℃ Cyclic Performance Test The lithium-ion batteries prepared in the above embodiments and comparative examples were charged and discharged at 45°C at a rate of 1C / 1C within the charge and discharge cutoff voltage range. The discharge capacity of the first cycle was recorded as C1, and the discharge capacity of the Nth cycle was recorded as C2. The capacity of the Nth cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate R2 = C2 / C1. The number of cycles of the lithium-ion battery when the cycle capacity retention rate R2 was 70% was recorded.
[0070] 0℃ Cyclic Performance Test The lithium-ion batteries prepared in the above embodiments and comparative examples were charged and discharged at 0°C at a rate of 1C / 1C within the charge and discharge cutoff voltage range. The discharge capacity of the first cycle was recorded as Y1, and the discharge capacity of the Nth cycle was recorded as Y2. The capacity of the Nth cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate of the Nth cycle, X2 = Y2 / Y1. The cycle number of the lithium-ion battery when the cycle capacity retention rate X2 was 70% was recorded.
[0071] The test results are entered into Table 2.
[0072] Table 2 As can be seen from the test results in Table 2, the test results of Examples 1-32 are significantly better than those of Comparative Examples 1-27. It is speculated that the reason is that the two types of additives in the examples form a synergistic effect with the oxide solid electrolyte, that is, the positive electrode contains an oxide solid electrolyte, the electrolyte contains a first additive of fluorinated phosphazene and a second additive of boron, and the contents of A, B and X meet the requirements of this application. Specifically, in Examples 1-5, the content of the first additive was gradually increased, and its high-temperature cycling performance was improved synchronously with the increase of the content of the first additive. The number of weeks in which the 45°C cycling capacity retention rate reached 70% increased from 619 weeks in Example 1 (A=0.1%) to 648 weeks in Example 2 (A=0.6%), 675 weeks in Example 3 (A=1.2%), 704 weeks in Example 4 (A=1.4%), and 709 weeks in Example 5 (A=2%). It is speculated that the reason is that as the content of the first additive increases, the electron blocking layer formed by the fluorinated phosphazene compound on the surface of the oxide solid electrolyte becomes more dense, which can more effectively inhibit the oxidative decomposition of the electrolyte and the dissolution of transition metals under high voltage, reduce the increase of interfacial impedance during cycling, and extend the high-temperature cycling life. In Examples 6-10, this group fixed the content of fluorinated phosphazene additives (A=0.6%) and oxide solid electrolyte content (X=1%), and gradually increased the content of the second additive (0.25%-2.5%). The corresponding high-temperature storage performance (60℃) was significantly improved with the increase of the content of the second additive, and the thickness expansion rate at 60℃ was significantly suppressed. The reason is that the higher the content of the second additive, the more empty orbitals of the B atoms in its boron compounds can complex with more HF and PF5 generated by electrolyte decomposition, reducing the corrosion of the oxide solid electrolyte by acidic species and reducing the rate of electrolyte decomposition gas generation, thereby significantly suppressing the battery thickness expansion during storage. In Examples 11-15, the oxide solid electrolyte content X% increased from 0.1% to 3%. As shown in Table 2, with the increase of X%, the number of cycles at 0°C in Examples 11-15 increased from 584 cycles to 813 cycles. This is because the higher the X% content, the denser the ion transport channels in the positive electrode active layer, which promotes ion migration at low temperatures. However, the thickness expansion rate at 60°C increased from 9.2% to 18.1% with the increase of X%, and the number of cycles at 45°C decreased from 675 cycles to 592 cycles. This is because the increase of X% increases the specific surface area of the solid electrolyte, and the fixed contents of A% and B% cannot fully cover the interface, leading to an increased risk of HF corrosion and electrolyte decomposition, and thus a deterioration in high-temperature performance. In Examples 16-19, Examples 16 (A / B=0.08) and 17 (A / B=0.09) have A / B ratios close to the lower limit, with 653 and 654 cycles at 0°C, 6.3% and 6.5% thickness expansion rates at 60°C, and 588 and 590 cycles at 45°C. Examples 18 (A / B=4) and 19 (A / B=3.27), with A / B ratios close to the upper limit, had 686 and 688 cycles at 0°C, 15.9% and 16.2% thickness expansion rates at 60°C, and 578 and 579 cycles at 45°C. Although some performance characteristics of these two examples were slightly lower than those of the examples with intermediate A / B ratios, they were significantly better than those of the comparative examples where the A / B ratio was not within the range specified in this application. This verifies the effectiveness of 0.08≤A / B≤4 in improving performance and synergistically maintaining battery stability.
[0073] In Examples 20-23, Examples 20-21 ((A+B) / X=0.23-0.28, A=0.2%-0.24%, B=0.25%-0.6%, X=3%), Table 2 shows that Examples 20-21 achieved 816-817 cycles at 0°C, 21.7%-22.7% expansion rate at 60°C (due to insufficient total additive content relative to X%, resulting in slightly weaker interface protection), and 573-574 cycles at 45°C, outperforming Comparative Example 24, which had (A+B) / X<0.23. Examples 22-23 ((A+B) / X=21.25-22, A=1.8%-2%, B=2.4%-2.45%, X=0.2%), Table 2 shows that the expansion rate at 60℃ is only 5.1%-5.3% (due to sufficient total amount of additives resulting in strong interface protection), and the number of cycles at 45℃ is 716-718 cycles, which is better than Comparative Example 26, which has (A+B) / X>22.
[0074] Compared with Example 2, Examples 24-32 differ in that the first additive in Examples 24-26 is changed from compound 1 to compounds 2, 3 and 4; the second additive in Examples 27-28 is changed from LiDFOB to LiBF4 and LiBOB; and the oxide solid electrolyte in Examples 29-32 is changed from LATP to LLZO, LAGP, LLTO and LTTP. Table 2 shows that there is no significant difference in the performance tests of Examples 24-32 compared with Example 2, thus verifying that the first additive, the second additive and the solid electrolyte specified in this application can maintain stable performance.
[0075] As can be seen from the parameter settings of Comparative Examples 1-27 in Table 1, all of Comparative Examples 1-27 do not meet the limiting conditions of 0.23≤(A+B) / X≤22, 0.08≤A / B≤4, and 0.1≤A≤2, 0.25≤B≤2.5, and 0.1≤X≤3. As can be seen from Table 2, the performance of the comparative examples is inferior to that of the embodiments. Furthermore, the number of cycles of Comparative Examples 1-7 (such as Comparative Example 1 without additives) at 0°C is only 341-519 cycles, the thickness expansion rate at 60°C is 20.7%-35.2%, and the number of cycles at 45°C is 269-472 cycles. Comparative Examples 8-13, 20-27 (Comparative Example 8 with A / B < 0.08, Comparative Example 26 with (A+B) / X > 22): 0℃ cycle count 414-638 cycles, 60℃ storage thickness expansion rate 6.8%-34.9%, 45℃ cycle count 417-618 cycles; Comparative Examples 14-19 (such as Comparative Example 14 where triethyl phosphate is used instead of the first additive of this application) had 454-465 cycles at 0°C and 391-399 cycles at 45°C. Overall, the comparative examples showed increased interfacial side reactions and hindered ion transport. In summary, the first additive can inhibit the excessive growth of the boron-based interfacial film of the second additive, achieving a good balance between high and low temperature performance. The combined use of the first and second additives improves high-temperature cycling, low-temperature cycling, and high-temperature storage performance. Furthermore, by controlling the mass percentages of the first additive A, the second additive B, and the oxide solid electrolyte X in the positive electrode active material, satisfying the relationships 0.23≤(A+B) / X≤22, 0.08≤A / B≤4, and 0.1≤A≤2, 0.25≤B≤2.5, and 0.1≤X≤3, the stability of the oxide solid electrolyte under high voltage can be improved while ensuring its enhancement of the ionic conductivity of the positive electrode. This allows for better synergistic effects and performance optimization.
[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode active material layer, which includes a positive electrode active material and an oxide solid electrolyte. The electrolyte includes a solvent, a lithium salt, a first additive, and a second additive. The first additive includes a fluorinated phosphazene compound, and the second additive includes a boron compound. The lithium-ion battery meets the following conditions: Equation 1: 0.23≤(A+B) / X≤22, 0.08≤A / B≤4, and 0.1≤A≤2, 0.25≤B≤2.5, 0.1≤X≤3; Wherein, A% is the mass percentage content of the first additive in the electrolyte; B% is the mass percentage of the second additive in the electrolyte; X% represents the mass percentage of the oxide solid electrolyte in the positive electrode active layer.
2. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery meets the following conditions: Equation 2: 0.28≤(A+B) / X≤21.
25.
3. The lithium-ion battery according to claim 1, characterized in that, The first additive and the second additive satisfy the following conditions: Equation 3: 0.09≤A / B≤3.
27.
4. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery satisfies at least one of the following conditions: （1）0.6≤A≤2； （2）0.5≤B≤2.4； （3）0.5≤X≤2。 5. The lithium-ion battery according to claim 1, characterized in that, The first additive includes at least one of the following fluorophosphazene compounds: 。 6. The lithium-ion battery according to claim 1, characterized in that, The second additive includes one or more of lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium dioxalate borate.
7. The lithium-ion battery according to claim 1, characterized in that, The oxide solid electrolyte includes one or more of lithium aluminum titanium phosphate, lithium lanthanum zirconate, lithium aluminum germanium phosphate, lithium lanthanum titanate, and lithium titanium phosphate.
8. The lithium-ion battery according to claim 1, characterized in that, The positive electrode active material includes a transition metal lithium oxide; the chemical formula of the transition metal lithium oxide is Li. 1+x Ni y Co z M (1-y-z) O2, where -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; M is selected from one or more of Mg, Zn, Ga, Ba, Al, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.
9. The lithium-ion battery according to claim 1, characterized in that, The solvent includes at least one selected from ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, propyl acetate, ethyl butyrate, propyl propionate, γ-butyrolactone, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.
10. An electrical appliance, characterized in that, The lithium-ion battery includes any one of claims 1-9.