Composite cathode material and preparation method thereof

Abstract

The application relates to the technical field of battery material preparation, and particularly discloses a composite positive electrode material and a preparation method thereof. The composite positive electrode material is composed of an inner core, an intermediate layer and an outer shell layer; the inner core is an oxide positive electrode material with a layered structure; the intermediate layer is an organic cross-linked structure and is composed of a cationic surfactant and an ion-conducting polymer; and the outer shell layer is an organic-inorganic heterostructure and is composed of an anionic surfactant and a phosphate or spinel positive electrode material. The outer shell layer contains a positive electrode material with stable structure, which can provide a more stable discharge platform. Meanwhile, the conductive polymer in the intermediate layer can act as a bridge between the two positive electrode materials to accelerate electron transmission. In addition, the oxygen in the surface structure of the inner core and the cationic surfactant can effectively clamp unstable oxygen through coordination, thereby avoiding the loss of oxygen and the migration of transition metal ions in the cycle process.

Description

Technical Field

[0001] This invention relates to the field of battery material preparation technology, and specifically discloses a composite cathode material and its preparation method. Background Technology

[0002] Currently, fossil fuels are the primary source of electricity, providing stable light for factories and urban infrastructure and drastically improving people's living conditions. However, the efficient utilization of clean energy has become a major development direction for the future. Among these, advanced energy storage technology is key to connecting renewable energy sources with the ever-increasing demand for electricity. Lithium-ion batteries, due to their high energy density and long lifespan, have emerged as an important electrochemical energy storage technology.

[0003] In lithium-ion batteries, the cathode material determines the upper limit of the battery's energy density and the total production cost, making it a crucial component. Although various lithium-ion intercalation / deintercalation cathode materials have emerged on the market, such as lithium cobalt oxide, ternary cathode materials, and lithium iron phosphate cathode materials, each type has its own unique advantages and unresolved disadvantages. Ternary cathode materials have relatively high energy density, but due to structural instability, they cannot achieve a long service life. Lithium-rich manganese-based oxide cathode materials, also layered materials, not only have a higher specific capacity than ternary cathode materials but also possess a significant cost advantage. However, their more complex crystal structure leads to extremely severe voltage decay. Spinel-type cathode materials have the advantages of low price and good performance, but their energy density is low at high temperatures. For structurally very stable polyanionic compounds, their reversible capacity is lower than the theoretical specific capacity, and they exhibit extremely poor electronic conductivity.

[0004] CN104733708B, CN111653752B, and CN104835985A all first preconstruct lithium iron phosphate precursors on the surface of ternary cathode materials, and then prepare lithium iron phosphate-coated ternary composite cathode materials through high-temperature calcination. However, one of the conditions for synthesizing lithium iron phosphate is the addition of a carbon source to the system, which is very unfavorable for the oxidizing transition metals in ternary materials, easily causing the ternary materials to deactivate, making the preparation conditions very harsh. CN113328085A and CN115863552A prepared lithium iron phosphate-coated ternary composite cathode materials and lithium iron phosphate / lithium manganese phosphate / lithium manganese iron phosphate-coated ternary composite cathode materials using ball milling and mechanical fusion methods, respectively. However, these two methods are only physical means, and after long-term cycling, the two different types of materials in close contact may delaminate, leading to structural breakage of the composite material. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention aims to provide a composite cathode material and a method for preparing the same.

[0006] In a first aspect, the present invention provides a composite cathode material, comprising a core, an intermediate layer and a shell layer. The core has a layered structure and comprises an oxide-based cathode material; the intermediate layer has an organic cross-linked structure and comprises a cationic surfactant and an ion-conductive polymer; the shell layer has an organic-inorganic heterostructure and comprises an anionic surfactant and a phosphate-based cathode material or a spinel-based cathode material.

[0007] Among them, the core comprises LiMO2, LiNi

[0011] , 1-a , 12 ,

[0010] , , a , , ,

[0012] Co x M’ y O2 (x>0, y>0), zLi2MnO3·(1-z)LiMO2 (0<z<1); M comprises at least one element of Ni, Co, and Mn; M’ comprises at least one element of Mn and Al.

[0008] The cationic surfactant in the intermediate layer comprises octadecyl trimethyl ammonium chloride, cetyl trimethyl ammonium chloride, cetyl trimethyl ammonium bromide, stearyl hydroxyethyl methyl sulfate ammonium, cetostearyl alcohol ether-2 O / W compound emulsifier, cetostearyl alcohol ether-21;

[0009] The ion-conductive polymer in the intermediate layer comprises polyethylene glycol, poly(ethylene oxide), poly(3,4-ethylenedioxythiophene), poly(1,3-dioxolane), polyurethane, lithium polyacrylate.

[0010] The anionic surfactant in the shell layer comprises sodium hexadecyl benzene sulfonate, sodium dodecyl alcohol polyoxyethylene ether sulfate, ammonium dodecyl sulfate, sodium dodecyl benzene sulfonate, triethanolamine lauryl sulfate, secondary alkyl sulfonate, fatty alcohol hydroxyethyl sulfonate, sodium N-lauroyl sarcosinate, sodium cocoyl methyl taurate, sodium N-lauroyl glutamate, amide polyoxyethylene ether magnesium sulfate, sodium lauryl alcohol polyoxyethylene ether carboxylate, dodecyl phosphate, potassium dodecyl phosphate, triethanolamine dodecyl phosphate, disodium dodecyl alcohol polyoxyethylene ether sulfosuccinate, alpha-olefin sulfonate.

[0011] The phosphate-based cathode material in the shell layer comprises LiM”PO4, Li3V2(PO4)3, LiVPO4F, LiMn a Fe 1-a PO4 (0<a<1), LiM”’P2O7 (M = V, Fe), LiM””P2O7; M” comprises at least one element of Fe, Ni, Co, and Mn; M”’ comprises at least one element of V and Fe; M”” comprises at least one element of Fe, Mn, Cu, and Co.

[0012] The spinel-based cathode material in the shell layer comprises LiMn2O4, Li2Mo4O9, Li4Mn5O 12.

[0013] The composite cathode material has cathode material particle sizes of 5–15 μm in the core and 0.002–1 μm in the shell.

[0014] The cathode material in the core includes polycrystalline particles and single-crystal particles.

[0015] The morphology of cathode materials includes spherical, sheet-like, and irregular block-like shapes.

[0016] The thickness of the intermediate layer and the outer shell is 1–10 nm.

[0017] Secondly, the preparation method of composite cathode material includes: fully dissolving an appropriate amount of cationic surfactant, anionic surfactant and ion-conducting polymer, then adding layered oxide cathode material and phosphate cathode material (or spinel cathode material), stirring for a period of time and then removing the solvent to obtain composite cathode material.

[0018] The beneficial effects of this invention are as follows:

[0019] This invention preferentially utilizes the association between ionicly conductive polymers and cationic surfactants in a solvent to form micelle aggregates, which are then adsorbed onto oxygen sites on the surface of a structurally unstable cathode material, forming an organic coating. Next, anionic surfactants can form micelles in the solvent and adsorb onto the transition metal sites of another type of cathode material. Through Coulomb interactions between the anionic and cation surfactants, the other type of cathode material is drawn to the vicinity of the anionic surfactant, forming a complete inorganic-organic coating. This coating is a shell layer containing a structurally stable cathode material and an organic coating such as a conductive polymer. The core is a structurally unstable cathode material. The outer shell containing a structurally stable cathode material provides a more stable discharge platform. Simultaneously, the conductive polymer in the intermediate layer acts as a bridge between the two cathode materials, accelerating electron transport. Furthermore, the oxygen in the core surface structure effectively clamps the unstable oxygen through coordination with the cationic surfactant, thereby preventing oxygen loss and transition metal ion migration during cycling. Attached Figure Description

[0020] Figure 1 Here are the XRD patterns of the electrode materials for Example 1 and Comparative Example 1;

[0021] Figure 2 SEM images of the electrode materials of Example 1 and Comparative Example 1;

[0022] Figure 3 This is a TEM image of the electrode material in Example 1. Detailed Implementation

[0023] The present application will be further described below with reference to specific embodiments. It should be understood that these specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0024] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0025] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0026] Example 1

[0027] Dissolve 0.04 g of hexadecyltrimethylammonium bromide and 0.04 g of polyethylene glycol in 2 ml of water, stir for 30 min, then add 0.02 g of sodium dodecylbenzenesulfonate. Subsequently, add 1 g of LiNi... 0.8 Co 0.1 Mn 0.1 O2 and 0.5 g of LiFePO4 were added to the above system as cathode material A and cathode material B, respectively. The solution was stirred at 90 °C for 6 h until the solution evaporated completely to obtain the composite cathode material.

[0028] Example 2

[0029] The difference from Example 1 is that the positive electrode material A is LiCoO2.

[0030] Example 3

[0031] The difference from Example 1 is that the cathode material A is LiNi. 0.8 Co 0.1 Al 0.1 O2.

[0032] Example 4

[0033] The difference from Example 1 is that the positive electrode material A is Li. 1.167 Ni 0.167 Co 0.167 Mn 0.5 O2.

[0034] Example 5

[0035] The difference from Example 1 is that the positive electrode material A is Li. 1.2 Mn 0.54 Co 0.13 Ni 0.13 O2.

[0036] Example 6

[0037] The difference from Example 1 is that the positive electrode material B is LiMn2O4.

[0038] Example 7

[0039] The difference from Example 1 is that the cathode material B is Li3V2(PO4)3.

[0040] Example 8

[0041] The difference from Example 1 is that the cathode material B is LiVPO4F.

[0042] Example 9

[0043] The difference from Example 1 is that the cathode material B is LiMn. 0.5 Fe 0.5 PO4.

[0044] Example 10

[0045] The difference from Example 1 is that the positive electrode material B is LiFeP2O7.

[0046] Example 11

[0047] The difference from Example 1 is that the cationic surfactant is octadecyltrimethylammonium chloride.

[0048] Example 12

[0049] The difference from Example 1 is that the cationic surfactant is stearyl hydroxyethyl methyl methyl sulfate ammonium.

[0050] Example 13

[0051] The difference from Example 1 is that the ion-conducting polymer is poly(3,4-ethylenedioxythiophene).

[0052] Example 14

[0053] The difference from Example 1 is that the ion-conducting polymer is lithium polyacrylate.

[0054] Example 15

[0055] The difference from Example 1 is that the anionic surfactant is ammonium dodecyl sulfate.

[0056] Example 16

[0057] The difference from Example 1 is that the anionic surfactant is dodecyl phosphate triethanolamine.

[0058] Comparative Example 1

[0059] The difference from Example 1 is that commercially available LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0060] Comparative Example 2

[0061] The difference from Example 1 is that hexadecyltrimethylammonium bromide and polyethylene glycol were not added.

[0062] Comparative Example 3

[0063] The difference from Example 1 is that sodium dodecylbenzenesulfonate was not added.

[0064] Cathode material performance testing

[0065] The positive electrode materials obtained in the examples and comparative examples were dissolved in NMP with a conductive agent and a binder at a mass ratio of 8:1:1, and then coated onto aluminum foil. After drying, the mixture was pressed into an electrode sheet with a diameter of 12 mm. Using this electrode sheet as the positive electrode, a lithium sheet as the negative electrode, and 1M LiPF6 dissolved in EC:DMC:EMC = 1:1:1 as the electrolyte, a 2025 button cell battery was assembled. The battery was then subjected to charge-discharge tests at the corresponding voltages, and the test results are shown in Table 1 below.

[0066] Table 1. Battery performance test results of Examples 1-16 and Comparative Examples 1-3

[0067]

[0068] As can be seen, the electrochemical results of Example 1 and Comparative Example 1 demonstrate that the composite material has better interfacial structural stability.

[0069] The electrochemical results of Examples 1-10 demonstrate that the synthesis method is adaptable to a variety of materials and exhibits good stability.

[0070] Furthermore, the electrochemical results of Examples 1, 11, and 12 indicate that cetyltrimethylammonium bromide is a better choice as the cationic surfactant. The electrochemical results of Examples 1, 13, and 14 indicate that polyethylene glycol is a better choice as the ion-conducting polymer. The electrochemical results of Examples 1, 15, and 16 indicate that sodium dodecylbenzenesulfonate is a better choice as the anionic surfactant.

[0071] The electrochemical results of Examples 1, 2, and 3 show that the absence of the intermediate layer or anionic surfactant affects the interfacial structure of the composite material.

[0072] Appendix Figure 1The figures show the X-ray diffraction patterns of the cathode materials obtained in Comparative Example 1 and Example 1. Comparative Example 1 is an unmodified layered ternary cathode material belonging to the R-3m space group. As can be seen from the figures, Example 1 and Comparative Example 1 both have similar diffraction patterns, indicating that the modification method does not change the structure of the core material. Due to the small amount of inorganic material in the outer shell, no diffraction peaks of lithium iron phosphate were observed in Example 1.

[0073] Appendix Figure 2 The image shows a scanning electron microscope (SEM) image of the binary core-shell composite cathode material obtained in Example 1. It can be observed that there is a significant coating on the material surface and the particle size of the composite material is approximately 10 μm.

[0074] Appendix Figure 3 This is a transmission electron microscope (TEM) image of the binary core-shell composite cathode material obtained in Example 1. A double-layer coating structure can be observed on the material surface, with the outermost layer containing lithium iron phosphate material encapsulated by organic matter.

[0075] In summary, this invention provides a method for preparing binary core-shell composite cathode materials. This method can leverage the advantages of other materials to compensate for the shortcomings of the core material, thereby obtaining a composite material with more stable chemical properties. Furthermore, this method has simple synthesis steps, low energy consumption, and is beneficial for industrial production.

Claims

1. A composite cathode material, characterized in that, The composite cathode material consists of a core, an intermediate layer, and an outer shell. Composition: The core is a layered oxide-based cathode material; the middle layer is an organic cross-linked structure composed of cationic surfactants and ion-conducting polymers; the outer shell is an organic-inorganic heterostructure composed of anionic surfactants and phosphate-based or spinel-based cathode materials. The ion-conducting polymer of the intermediate layer is one or more of polyethylene glycol, polyethylene oxide, poly(3,4-ethylenedioxythiophene), poly(1,3-dioxane), and lithium polyacrylate. The particle sizes of the positive electrode materials in the core and the outer shell are 5~15 µm and 0.002~1 µm, respectively; the thickness of the intermediate layer and the outer shell is 1~10 nm.

2. The composite cathode material according to claim 1, characterized in that, The oxide-based cathode material is: LiMO2, LiNi. 1-x-y Co x M' y One of O2, zLi2MnO3·(1-z)LiMO2, wherein M is an element selected from Ni, Co, and Mn; M' is at least one element selected from Mn and Al, x≥0.05, y≥0.05, 0 <z<1。 3. The composite cathode material according to claim 1, characterized in that, The cationic surfactant in the intermediate layer is one or more of octadecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, and stearyl hydroxyethyl methyl ammonium sulfate.

4. The composite cathode material according to claim 1, characterized in that, The anionic surfactant of the outer shell layer is one or more of the following: sodium hexadecylbenzenesulfonate, sodium dodecyl alcohol polyoxyethylene ether sulfate, ammonium dodecyl sulfate, sodium dodecylbenzenesulfonate, triethanolamine lauryl sulfate, sodium secondary alkyl sulfonate, sodium fatty alcohol hydroxyethyl sulfonate, sodium N-lauroyl sarcosinate, sodium coconut methyl taurate, sodium N-lauroyl glutamate, magnesium amide polyoxyethylene ether sulfate, sodium lauryl polyoxyethylene ether carboxylate, dodecyl phosphate, potassium dodecyl phosphate, triethanolamine dodecyl phosphate, disodium dodecyl alcohol polyoxyethylene ether sulfosuccinate, and sodium α-alkenyl sulfonate.

5. The composite cathode material according to claim 1, characterized in that, The phosphate-based cathode material of the outer shell layer is LiM''PO4, Li3V2(PO4)3, LiVPO4F, or LiMn. a Fe 1-a PO4, wherein 0 < a < 1, LiM'''P2O7, one of LiM''''P2O7; M'' is at least one of Fe, Ni, Co, and Mn; M''' is at least one of V and Fe; M'''' is at least one of Fe, Mn, Cu, and Co.

6. The composite cathode material according to claim 1, characterized in that, The spinel-type cathode material of the outer shell layer is LiMn2O4, Li2Mo4O9, or Li4Mn5O4. 12 One of them.

7. A method for preparing the composite cathode material according to claim 1, characterized in that, The preparation method is as follows: cationic surfactant, anionic surfactant and ion-conducting polymer are fully dissolved, and then layered oxide cathode material and phosphate cathode material or spinel cathode material are added. After stirring, the solvent is removed to obtain composite cathode material.

Images