High-nickel positive electrode interface modification additive and lithium ion battery
By constructing an inorganic-organic composite CEI on the surface of a high-nickel cathode and utilizing the strong adsorption mechanism of aromatic ring-bridged phosphate compounds at multiple anchor points, the problem of electrolyte oxidation and decomposition of high-nickel cathode materials during cycling was solved, thereby improving the cycle stability and safety of the battery.
Patent Information
- Application Number
- CN202610059176.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-16
- Publication Date
- 2026-05-01
AI Technical Summary
High-nickel cathode materials undergo electrolyte oxidation and decomposition during cycling due to the lack of electron states on their surface, forming an unstable interface layer. This leads to battery capacity decay and structural degradation, affecting cycle life and safety performance.
Aromatic ring-bridged phosphate compounds with a multi-anchor strong adsorption mechanism are used as additives to construct an inorganic-organic composite enhanced electrolyte interface (CEI) film on the surface of a high-nickel cathode. Through the binding of multiple phosphate groups with Ni4+ sites, a conjugated organic carbon network is formed and intertwined with inorganic lithium salt, providing mechanical strength and chemical stability.
It achieves long-term stable adsorption on the surface of high-nickel cathode, improves the cycle stability and safety of the battery under high voltage, suppresses the side reactions between the electrolyte and the cathode, and extends the battery life.
Smart Images
Figure CN121964852A_ABST
Abstract
Description
A high-nickel cathode interface modification additive and a lithium-ion battery Technical Field
[0001] This invention relates to the field of lithium-ion battery technology, specifically to a novel electrolyte additive, an electrolyte containing the additive, and its application in high-nickel ternary cathode lithium-ion batteries. Background Technology
[0002] High-nickel layered oxide cathode materials (such as LiNi) 0.8 Co 0.1 Mn 0.1 O2 (NCM811) is considered a key cathode material for next-generation high-energy-density lithium-ion batteries due to its high specific capacity and high energy density. However, with increasing nickel content, the material exhibits a high degree of electron-deficient states on its surface during cycling, especially under high-voltage (>4.3V) charging conditions (such as Ni). 4+ (Enrichment). Such an electron-deficient state has a strong tendency to steal electrons from the surrounding electrolyte, thus exhibiting extremely strong "aggressiveness" towards organic electrolysis and violently catalyzing the oxidative decomposition of the electrolyte. This process not only consumes active lithium and electrolyte, leading to battery capacity decay and gas production, but also causes by-reaction products to form an unstable and excessively thick interface layer on the positive electrode surface, increasing interfacial impedance and accelerating the structural degradation of the positive electrode material (such as rock salt phase transformation and grain boundary crack propagation), severely restricting the cycle life and safety performance of high-nickel batteries.
[0003] To address the aforementioned issues, introducing functional additives into the electrolyte is a highly economical and effective strategy. These additives preferentially react on the cathode surface to form a stable cathode electrolyte interphase (CEI), physically isolating the electrolyte from the highly active cathode. While traditional additives such as vinylene carbonate and fluoroethylene carbonate have some effect, the CEI they form lacks sufficient mechanical and chemical stability at high cutoff voltages, and is not particularly effective in addressing the unique interfacial problems of high-nickel cathodes, making it difficult to provide long-term protection for them.
[0004] Phosphate esters (such as trimethyl phosphate) are used due to their excellent flame retardant properties and ability to form Li-rich compounds. x PO y The electrode-electrolyte interface has attracted much attention, but due to its simple molecular structure, the resulting CEI is loose and easily destroyed, failing to effectively isolate the electrode from the electrolyte. Therefore, there is an urgent need to develop a novel additive that can efficiently anchor to the surface of a high-nickel cathode and construct a high-strength, high-stability CEI to solve the problem of cathode / electrolyte interface instability during charging of high-nickel electrodes. Summary of the Invention
[0005] To address the above technical problems, the present invention aims to provide a functional additive, a gel electrolyte, and a lithium-ion battery, which can construct an "inorganic-organic" composite enhanced CEI in situ on the surface of a high-nickel cathode through a multi-anchor strong adsorption mechanism. This aims to solve the problems of poor cycle life caused by severe electrolyte oxidation and decomposition and unstable CEI in existing high-nickel ternary cathode batteries.
[0006] To achieve the above objectives, the present invention adopts the following technical solution: On one hand, the present invention provides an interface modification additive for high-nickel cathodes of lithium-ion batteries, which is an aromatic ring-bridged phosphate compound having the following general formula: [(RO)] m P(=O)] k – L – [P(=O)(OR) n ] j Wherein, L is a rigid aromatic or alicyclic linker, such as phenylene, biphenyl dimethyl, cyclohexane dimethyl, etc., which gives the molecule an overall rigid structure; R is an alkyl or fluoroalkyl group; m, n are 1 or 2; k, j are 1 or 2, and k+j ≥ 2, which means that each molecule contains at least two phosphate ester groups.
[0007] The core design concept of this invention lies in: strong adsorption through multiple anchor points: multiple phosphoryl groups (P=O) in the molecule act as Lewis base sites, which can synergistically adsorb onto multiple adjacent Lewis acids (such as Ni) on the surface of the high-nickel cathode during battery charging. 4+ At the ) site, a "chelation" effect is formed. This multi-site adsorption binding force is much stronger than the single-site adsorption of traditional monophosphate esters, ensuring that the additive is more efficient, more robust, and selectively enriched at the positive electrode interface under high pressure. Simultaneously, during the electrochemical oxidation process, the additive molecules undergo "self-sacrificial" decomposition, with the phosphate ester groups decomposing to produce substances such as Li x PF y O z Inorganic lithium salts such as LiF provide a fast lithium-ion transport channel.
[0008] Aromatic ring-assisted high-efficiency film formation: The rigid aromatic or alicyclic skeleton (L) in the additive molecule is not easily completely decomposed under oxidative conditions. Instead, it forms a dense organic carbon network with a conjugated structure through partial cross-linking. This organic network, as the "skeleton," intertwines with the aforementioned inorganic lithium salt "filler" to form an "inorganic-organic" composite CEI, which possesses excellent ionic conductivity, electronic insulation, mechanical strength, and chemical stability.
[0009] Preferably, the additive is a symmetrical or asymmetrical bisphosphonate, triphosphonate, etc., and specific examples include, but are not limited to, 1,4-bis(diethoxyphosphono)benzene and its fluorinated derivatives.
[0010] On the other hand, the present invention also provides an interface-modified gel electrolyte for a high-nickel cathode, comprising a polymer network, a lithium salt, an organic solvent, and the aforementioned aromatic ring-bridged phosphate additive.
[0011] Furthermore, the interface-modified gel electrolyte is characterized in that the content of the additive is 0.1% to 5% of the total mass of the gel electrolyte.
[0012] Furthermore, the interface-modified gel electrolyte is characterized in that the polymer gel network is formed by in-situ polymerization of an acrylate crosslinking agent or a methacrylate crosslinking agent; the crosslinking agent includes one or more of polyethylene glycol diacrylate, pentaerythritol tetraacrylate, and ethylene glycol dimethacrylate.
[0013] Furthermore, the interface-modified gel electrolyte is characterized in that the lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium difluorooxalate borate; and the organic solvent is selected from one or more of ethylene carbonate, fluoroethylene carbonate, methyl ethyl carbonate, diethyl carbonate, and ethylene glycol dimethyl ether.
[0014] Combining the additives of this invention with gel electrolytes has synergistic advantages: confinement and sustained release of the gel polymer network: the three-dimensional network structure of the gel can restrict the free diffusion of large-volume aromatic ring-bridged phosphate molecules, allowing them to accumulate near the positive electrode interface for a longer period of time, thus achieving long-term stable adsorption.
[0015] Physical-chemical dual stability: When the gel electrolyte undergoes in-situ polymerization, it can act as a physical barrier to coat the positive electrode particles and suppress interfacial failure caused by changes in electrode volume. Meanwhile, the chemical CEI constructed by the additives provides intrinsic interfacial passivation. The combination of the two achieves a dual improvement in interfacial stability.
[0016] Furthermore, the present invention also provides a lithium-ion battery comprising the aforementioned gel electrolyte, wherein the cathode is made of a high-nickel material (Ni ≥ 80%), and the charging cut-off voltage can reach 4.5V or higher. This battery exhibits significantly improved high-voltage cycle stability.
[0017] Compared with the prior art, the present invention has the following advantages and technical effects: 1. The adsorption and film formation efficiency of additives are doubled: Based on the Lewis acidity exhibited by the high nickel cathode in the charging state due to the lack of electrons, the functional groups of Lewis basic phosphate esters rich in electrons are used as active sites for Lewis acid-base interaction to achieve the directional adsorption of additives. At the same time, multiple phosphate ester sites are introduced to enhance the adsorption capacity, and they are integrated into a single molecule through rigid connecting groups, thereby achieving multi-anchor point, high-strength, and specific adsorption on the surface of the high nickel cathode, and an inorganic-organic composite enhanced CEI is constructed in situ.
[0018] 2. Improved interfacial film-forming performance: By introducing a rigid aromatic or alicyclic framework, a dense organic carbon network with a conjugated structure is formed on the cathode surface. This network mixes with the inorganic components formed by the decomposition of phosphate esters to form an "inorganic-organic" composite interfacial layer. The resulting composite CEI combines the ionic conductivity of the inorganic phase with the mechanical toughness and chemical inertness of the organic framework phase, effectively isolating the electrolyte from the cathode and suppressing transition metal dissolution and interfacial side reactions.
[0019] 3. Additive-polymer synergistic effect: Combining the additive system with the gel electrolyte system achieves a perfect unity of chemical modification of additives and physical stability of polymers, providing comprehensive and long-lasting interface protection measures for high-nickel cathodes. Attached Figure Description
[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 is a comparison of the cycle performance of the battery prepared in Comparative Example 1 at cutoff voltages of 4.4V and 4.5V.
[0021] Figure 2 is a comparison of the cycle performance of the battery prepared in Example 1 at cutoff voltages of 4.4V and 4.5V. Detailed Implementation
[0022] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Embodiments
[0023] This embodiment provides a method for preparing an interface-modified gel electrolyte for NCM811 cathode and assembling the battery: Solution A preparation: In an argon-filled glove box (O2 < 0.5 ppm, H2O < 0.1 ppm), lithium difluorooxalate borate was dissolved at a concentration of 1 M in a mixed solvent of fluoroethylene carbonate and ethylene glycol dimethyl ether at a volume ratio of 3:7, and magnetically stirred until completely transparent.
[0024] Preparation of Solution B: In a glove box filled with argon (O2<0.5ppm, H2O<0.1ppm), add 1,4-bis(diethoxyphosphono)benzene (additive) and pentaerythritol tetraacrylate (crosslinking agent) to Solution A at a mass ratio of 2:10, and stir magnetically until homogeneous.
[0025] Preparation of precursor solution: Add 0.5% (by mass of monomer) of azobisisobutyronitrile to solution B as a thermal initiator, stir until homogeneous, and obtain a homogeneous and transparent precursor solution.
[0026] Battery assembly: NCM811 was used as the positive electrode active material (loading approximately 4 mg / cm³). 2 A lithium-ion battery was prepared using lithium metal as the negative electrode and polypropylene (PP) as the separator. Appropriate amounts of precursor solution were added dropwise to both the positive and negative electrode sides. The mixture was allowed to stand at 25°C for 24 hours, followed by thermal polymerization at 70°C for 2 hours to form a gel electrolyte. Example
[0027] This embodiment provides a method for preparing an interface-modified gel electrolyte for NCM811 cathode and assembling the battery: Solution A preparation: In an argon-filled glove box (O2 < 0.5 ppm, H2O < 0.1 ppm), lithium hexafluorophosphate is dissolved at a concentration of 1 M in a mixed solvent of fluoroethylene carbonate and methyl ethyl carbonate at a volume ratio of 5:5, and magnetically stirred until completely transparent.
[0028] Preparation of Solution B: In a glove box filled with argon (O2<0.5ppm, H2O<0.1ppm), add 1,4-bis(bis(2,2,2-trifluoroethoxy)phosphono)benzene (additive) and polyethylene glycol diacrylate (crosslinking agent) to Solution A at a mass ratio of 3:10, and stir magnetically until homogeneous.
[0029] Preparation of precursor solution: Add 0.5% (by mass of monomer) of azobisisobutyronitrile to solution B as a thermal initiator, stir until homogeneous, and obtain a homogeneous and transparent precursor solution.
[0030] Battery assembly: NCM811 was used as the positive electrode active material (loading approximately 4 mg / cm³). 2 A lithium-ion battery was prepared using lithium metal as the negative electrode and polypropylene (PP) as the separator. Appropriate amounts of precursor solution were added dropwise to both the positive and negative electrode sides. The mixture was allowed to stand at 25°C for 24 hours, followed by thermal polymerization at 70°C for 3 hours to form a gel electrolyte. Example
[0031] This embodiment provides a method for preparing an interface-modified gel electrolyte for NCM811 cathode and assembling the battery: Solution A preparation: In an argon-filled glove box (O2 < 0.5 ppm, H2O < 0.1 ppm), lithium bis(trifluoromethanesulfonyl)imide was dissolved at a concentration of 1 M in a mixed solvent of fluoroethylene carbonate and diethyl carbonate at a volume ratio of 3:7, and magnetically stirred until completely transparent.
[0032] Preparation of Solution B: In a glove box filled with argon (O2<0.5ppm, H2O<0.1ppm), add 4,4'-bis(diethoxyphosphono)biphenyl (additive) and ethylene glycol dimethacrylate (crosslinking agent) to Solution A at a mass ratio of 2:10, and stir magnetically until homogeneous.
[0033] Preparation of precursor solution: Add 0.5% (by mass of monomer) of azobisisobutyronitrile to solution B as a thermal initiator, stir until homogeneous, and obtain a homogeneous and transparent precursor solution.
[0034] Battery assembly: NCM811 was used as the positive electrode active material (loading of approximately 4 mg / cm2), lithium metal as the negative electrode, and polypropylene (PP) as the separator. Appropriate amounts of precursor solution were added dropwise to both the positive and negative electrode sides, and the mixture was allowed to stand at 25°C for 24 hours. Subsequently, it was thermally polymerized at 70°C for 3 hours to form a gel electrolyte, thus obtaining the lithium-ion battery.
[0035] The difference between Comparative Example 1 and Example 1 is that no phenyl phosphate additives were added to the gel electrolyte precursor solution when preparing solution B; the remaining steps were the same as in Example 1.
[0036] The difference between Comparative Example 2 and Example 1 is that no cross-linking agent was added to the gel electrolyte precursor solution when preparing solution B; the remaining steps were the same as in Example 1.
[0037] The difference between Comparative Example 3 and Example 1 is that, in preparing solution B, an equal mass of the conventional monophosphate additive triethyl phosphate was added to the gel electrolyte precursor solution instead of the additive involved in this invention; the remaining steps were the same as in Example 1.
[0038] The lithium-ion batteries prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to long-cycle performance tests. The corresponding batteries were subjected to long-cycle tests at a 1C rate within the voltage range of 3-4.4 V and 3-4.5 V, respectively. The capacity retention rate of the batteries after 200 cycles was recorded, and the results are shown in Table 1.
[0039] As shown in the table above, the gel electrolytes containing the aromatic ring-bridged phosphate ester additive of the present invention (Examples 1-3) exhibit better cycle stability at a cutoff voltage of 4.4V than Comparative Example 1 without the additive, demonstrating that the additive can effectively improve the cycle stability of the battery. Simultaneously, the gel electrolytes containing the aromatic ring-bridged phosphate ester additive of the present invention (Examples 1-3) exhibit better cycle stability at a cutoff voltage of 4.4V than Comparative Example 2 with the electrolyte system, demonstrating the beneficial effect of the gel polymer system on battery stability. Furthermore, the gel electrolytes containing the aromatic ring-bridged phosphate ester additive of the present invention (Examples 1-3) exhibit better cycle stability at a cutoff voltage of 4.4V than Comparative Example 3 with the conventional phosphate ester additive, demonstrating that the polyphosphoryl group in the present invention effectively enhances the binding effect of the additive on the positive electrode surface, thereby improving the cycle stability of the battery. It is worth noting that when the cutoff voltage is increased to 4.5V, due to the high electron deficiency state of the positive electrode, the NCM811 catalyzed electrolyte decomposition is further aggravated, and the cycle stability of Comparative Examples 1-3 shows a significant decrease in capacity retention compared to the cutoff voltage of 4.4V. The gel electrolytes containing the aromatic ring-bridged phosphate additive of the present invention (Examples 1-3) maintained a relatively high capacity retention rate after the cutoff voltage was increased to 4.5V due to the strong adsorption and film-forming protection effect of the additive on NCM811. This also proves the effective role of the aromatic ring-bridged phosphate additive in directional adsorption on the positive electrode surface under high voltage, thereby generating a highly stable interface layer and improving the battery cycle performance.
[0040] Figure 1 shows the charge-discharge cycle test results of the NCM811 lithium-ion battery assembled in Comparative Example 1 of this invention at a 1C rate for 200 cycles within voltage ranges of 3-4.4V and 3-4.5V. As shown in Figure 2, when the cutoff voltage is increased from 4.4V to 4.5V, the NCM811 cathode exhibits a stronger tendency to extract electrons from the surrounding electrolyte at this higher cutoff voltage, resulting in more severe electrolyte decomposition and a significant decrease in battery cycle stability.
[0041] Figure 2 shows the charge-discharge cycle test results of the NCM811 lithium-ion battery assembled in Example 1 of the present invention at a 1C rate for 200 cycles within voltage ranges of 3-4.4V and 3-4.5V. As shown in Figure 2, at a cutoff voltage of 4.5V, the strongly electron-deficient state of the NCM811 cathode induces more phenyl phosphate molecules to combine and decompose at the interface. This forms a stable interface layer that isolates the electrolyte and electrode, providing effective protection, and thus the capacity retention rate does not show a significant decrease when the cutoff voltage is increased to 4.5V.
[0042] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.
Claims
1. A high-nickel cathode interface modification additive, characterized in that, It is an aromatic ring-bridged phosphate compound with the following general formula: [(RO)] m P(=O)] k – L – [P(=O)(OR) n ] j Wherein, L is a linking group selected from phenylene, substituted phenylene, biphenyl diyl, naphthyl diyl, and cyclohexane-1,4-diyl; each R is independently selected from C1-C6 alkyl or C1-C6 fluoroalkyl; m and n are each independently 1 or 2; k and j are each independently 1 or 2, and satisfy k+j ≥ 2.
2. The interface modification additive according to claim 1, characterized in that, In the general formula, L is 1,4-phenylene, 2,5-difluoro-1,4-phenylene, 4,4'-biphenyldiyl, or 1,4-cyclohexanediyl.
3. The interface modification additive according to claim 1 or 2, characterized in that, The additive is selected from the following compounds: 1,4-bis(diethoxyphosphono)benzene, 1,4-bis(bis(2,2,2-trifluoroethoxy)phosphono)benzene, 1,3-bis(dimethoxyphosphono)benzene, 1-(diethoxyphosphono)-4-(bis(2,2,2-trifluoroethoxy)phosphono)benzene, 1,3,5-tris(diethoxyphosphono)benzene, 4,4'-bis(diethoxyphosphono)biphenyl, and 1,4-bis(diethoxyphosphono)cyclohexane.
4. An interface-modified gel electrolyte for high-nickel cathodes, characterized in that, It comprises a polymer gel network, a lithium salt, an organic solvent, and an aromatic ring-bridged phosphate additive as described in any one of claims 1-3.
5. The interface-modified gel electrolyte according to claim 4, characterized in that, The additive content is 0.1% to 5% of the total mass of the gel electrolyte.
6. The interface-modified gel electrolyte according to claim 4, characterized in that, The polymer gel network is formed by in-situ polymerization of acrylate crosslinking agents or methacrylate crosslinking agents; the crosslinking agents include one or more of polyethylene glycol diacrylate, pentaerythritol tetraacrylate, and ethylene glycol dimethacrylate.
7. The interface-modified gel electrolyte according to claim 4, characterized in that, The lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium difluorooxalate borate; the organic solvent is selected from one or more of ethylene carbonate, fluoroethylene carbonate, methyl ethyl carbonate, diethyl carbonate, and ethylene glycol dimethyl ether.
8. A method for preparing an interface-modified gel electrolyte as described in any one of claims 4-7, characterized in that, Includes the following steps: S1: Dissolve the lithium salt in an organic solvent to obtain solution A; S2: Mix the additives and optional crosslinking agents according to any one of claims 1-3 with solution A to obtain solution B; S3: Add an initiator to solution B to obtain a gel electrolyte precursor solution; S4: Inject the precursor solution into the battery assembly and thermally initiate an in-situ polymerization reaction to form the interface-modified gel electrolyte.
9. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte is the interface-modified gel electrolyte as described in any one of claims 4-7, and the active material of the positive electrode is a high-nickel positive electrode with a nickel content ≥80% LiNi. x Co y Mn z O2 (NCM, x≥0.8) or LiNi x Co y Mn z O2 (NCA, x≥0.8) material.
10. The lithium-ion battery according to claim 9, characterized in that, The charging cutoff voltage of the battery is not less than 4.3V (vs. Li). + / Li).