Titanium-based composite negative electrode material, sol-gel method for preparing same, solid-phase method for preparing same and lithium ion battery

Abstract

The application discloses a titanium-based composite negative material, a sol-gel method for preparing the same, a solid-phase method for preparing the same and a lithium ion battery. The titanium-based composite negative material is suitable for the lithium ion battery and comprises Y2Ti2O7 and LiYTiO4. The mass percentage of Y2Ti2O7 is 5-25%. The titanium-based composite negative material has a low lithium intercalation potential and a high specific capacity, is beneficial to improving the energy density of the battery, and does not contain flammable components, and has high safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium power energy materials, in particular to a titanium-based composite negative electrode material, a sol-gel method for preparing the same, a solid-phase method for preparing the same and a lithium ion battery. BACKGROUND

[0002] With the vigorous development of new energy vehicles and low-altitude economy, lithium ion batteries continue to make breakthroughs in terms of rate charge and discharge performance and energy density. At present, graphite is commonly used as a negative electrode material in commercial lithium ion batteries, but its overcharge resistance is poor, and lithium dendrite growth is easily triggered under overcharge conditions, which significantly threatens the safety performance of the battery.

[0003] To improve safety, titanium-based materials have gradually attracted attention, for example, lithium titanate, titanium niobium oxide (TiNb x O y , x, y represent atomic proportions) and the like. Such materials have a stable crystal structure, which can effectively inhibit the generation of lithium dendrites and avoid the risk of thermal runaway. However, the existing titanium-based materials have a high lithium intercalation potential / working potential (usually higher than 1.5V vs. Li + / Li), which results in a generally low specific capacity, making it difficult for full batteries equipped with such negative electrodes to meet the needs of high endurance application scenarios, thereby limiting their large-scale commercial application.

[0004] Therefore, there is an urgent need to develop a new type of negative electrode material that combines high safety and high energy density to further promote the application of lithium ion battery technology in high-end power and energy storage fields.

[0005] The statements herein only provide background technology related to the present application, and do not necessarily constitute the prior art. SUMMARY

[0006] The purpose of the present application is to provide a titanium-based composite negative electrode material, a sol-gel method for preparing the same, a solid-phase method for preparing the same and a lithium ion battery, in order to overcome the defects of low safety and low energy density of existing negative electrode materials.

[0007] In order to achieve the above purpose, the present application provides a titanium-based composite negative electrode material suitable for lithium ion batteries, which is composed of Y2Ti2O7 and LiYTiO4; wherein the mass percentage of Y2Ti2O7 is 5% to 25%.

[0008] Optionally, the mass percentage of Y2Ti2O7 is 7% to 17.5%.

[0009] Correspondingly, the present application also provides a sol-gel method for preparing the above-mentioned titanium-based composite negative electrode material, comprising:

[0010] Step 1, preparation of precursor: a soluble yttrium source, a soluble titanium source and an acidic complexing agent are dissolved in a solvent, a solution containing sodium compound is added, and the pH value is adjusted to obtain a complex sol containing Na, Ti and Y elements, and the complex sol is aged to allow polycondensation between Ti-containing and Y-containing colloidal particles to form a dry gel with a three-dimensional network structure; after natural cooling, the precursor is obtained by grinding;

[0011] Step 2, high-temperature heat treatment of the precursor to obtain a NaYTiO4 and Y2Ti2O7 composite material; the high-temperature heat treatment temperature T1 is 900℃ < T1 < 1200℃;

[0012] Step 3, ion exchange of the NaYTiO4 and Y2Ti2O7 composite material with a lithium salt by melt ion exchange to obtain the titanium-based composite negative electrode material.

[0013] Optionally, in step 1, the pH value is 6.5-7.5.

[0014] Optionally, in step 1, the molar ratio of sodium ions in the sodium compound solution to titanium ions in the titanium source is 1:1-1.5:1; and in step 3, the molar ratio of lithium ions in the lithium salt to sodium ions in the NaYTiO4 and Y2Ti2O7 composite material is 1.5:1-3:1.

[0015] Optionally, step 1 comprises:

[0016] Step 1.1, heating the complex sol at 60-100℃ to evaporate the solvent to obtain a pre-gel;

[0017] Step 1.2, heating the pre-gel at 100-200℃ to age the pre-gel to allow polycondensation between Ti-containing and Y-containing colloidal particles to form a dry gel with a three-dimensional network structure. Optionally, step 3 comprises: exchanging the NaYTiO4 and Y2Ti2O7 composite material with a lithium salt at 300-600℃ for 2-6h, then adding distilled water and stirring after natural cooling, centrifuging to obtain the titanium-based composite negative electrode material.

[0018] Correspondingly, the application also provides a solid phase method for preparing the above-mentioned titanium-based composite negative electrode material, comprising:

[0019] Step 1, grinding and mixing yttrium oxide, titanium oxide and sodium salt, and heating to allow solid phase synthesis to obtain a NaYTiO4 and Y2Ti2O7 composite material; the heating temperature T2 is 900℃ < T2 < 1200℃;

[0020] Step 2: The composite material of NaYTiO4 and Y2Ti2O7 is subjected to ion exchange with lithium salt. The ion exchange method is molten ion exchange to obtain the titanium-based composite anode material.

[0021] Optionally, in step 1, the molar ratio of sodium ions in the sodium salt to titanium ions in the titanium oxide is 1:1 to 1.5:1; in step 2, the molar ratio of lithium ions in the lithium salt to sodium ions in the composite material of NaYTiO4 and Y2Ti2O7 is 1.5:1 to 3:1.

[0022] Optionally, in step 2, the molten ion exchange is performed by exchanging the NaYTiO4 and Y2Ti2O7 composite material with lithium salt in a mixed powder obtained by ball milling or grinding at 300℃~600℃ for 2h~6h.

[0023] Accordingly, the present invention also provides a lithium-ion battery, wherein the negative electrode is made of the above-mentioned titanium-based composite negative electrode material.

[0024] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0025] This invention provides a titanium-based composite anode material composed of Y₂Ti₂O₇ and LiYTiO₄; wherein the mass percentage of Y₂Ti₂O₇ is 5%~25%. In the titanium-based composite material, Y₂Ti₂O₇... 3+ The introduction of [something] weakens the strength of the Ti-O bond, making Li [something] [something]. + When embedding Ti 4+ Reduced to Ti 3+ The energy barrier required for this process is lowered, thereby reducing the lithium intercalation potential of the entire titanium-based composite material to 0.1V~0.3V vs. Li. + The L / Li composite anode material exhibits a significantly lower lithium intercalation potential compared to existing titanium-based materials, thereby effectively increasing the single-cell voltage of the full battery. Simultaneously, the interface formed by the Y2Ti2O7 and LiYTiO4 phases serves as a rapid lithium-ion migration channel, facilitating efficient lithium-ion diffusion and enhancing ion conduction. Ultimately, this results in a specific capacity ≥200 mAh / g for the titanium-based composite anode material, higher than existing titanium-based materials (e.g., lithium titanate has a specific capacity of approximately 175 mAh / g). The combined effect of the reduced lithium intercalation potential and increased specific capacity significantly improves the energy density of the full battery. Furthermore, the titanium-based composite anode material is composed of metal oxides and is non-flammable, thus offering greater safety than traditional graphite materials.

[0026] The application further provides a sol-gel method and a solid-phase method for preparing the titanium-based composite negative electrode material, wherein the relative proportion of Y2Ti2O7 phase and LiYTiO4 phase in the titanium-based composite negative electrode material can be controlled by adjusting the temperature in the high-temperature heat treatment step (step 102 described below) of the sol-gel method or the solid-phase synthesis reaction step (step 201 described below) of the solid-phase method, which is simple to operate and beneficial to saving production cost. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 A flow chart of the sol-gel method for preparing the titanium-based composite negative electrode material according to the application.

[0028] Figure 2 A flow chart of the solid-phase method for preparing the titanium-based composite negative electrode material according to the application.

[0029] Figure 3 A charge-discharge curve of the titanium-based composite material obtained in Example 1.

[0030] Figure 4 X-ray diffraction patterns of the materials prepared in Examples 1-2 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0031] The titanium-based composite negative electrode material, the sol-gel method for preparing the same, the solid-phase method for preparing the same and the lithium ion battery according to the application will be further described in detail below in combination with the drawings and specific embodiments. The advantages and features of the application will be more apparent according to the following description. It should be noted that the drawings are greatly simplified and all use non-precise proportions, only for the purpose of facilitating and clarifying the description of the embodiments of the application. In order to make the purposes, features and advantages of the application more apparent and easy to understand, please refer to the drawings. It should be understood that the structures, proportions, sizes, etc. shown in the drawings attached to the specification are only used to understand and read by those skilled in the art, and are not used to limit the conditions for implementing the application, so they do not have technical significance. Any modification of the structure, change of the proportion relationship or adjustment of the size, without affecting the effect and purpose that can be achieved by the application, should still fall within the scope of the technical content disclosed by the application.

[0032] The "lithium intercalation potential" described herein refers to the equilibrium electrode potential exhibited by the negative electrode material relative to a metal lithium reference electrode when lithium ions are removed from the positive electrode and intercalated into the interior of the negative electrode active material lattice during the charging process of the lithium ion battery. The theoretical operating voltage of the full battery is essentially equal to the difference between the delithiation potential of the positive electrode and the lithium intercalation potential of the negative electrode, and reducing the lithium intercalation potential of the negative electrode is an effective way to directly improve the energy density of the battery.

[0033] The specific capacity described herein refers to the amount of charge that can be stored or released by the electrode material per unit mass, which directly reflects the ability of the material to store energy, and the unit of specific capacity is mAh / g.

[0034] As described in the background, the existing negative electrode material of lithium ion battery still has obvious deficiencies in safety and energy density. Specifically, the graphite material is easy to cause lithium dendrite growth in the charging and discharging process, and then causes the risk of short circuit and thermal runaway, which has significant safety hazards. Although the existing titanium-based material has high safety, its lithium intercalation potential (about 1.5V vs. Li + / Li) is too high, and the too high lithium intercalation potential will cause the single cell voltage of the full battery to be low, and the theoretical specific capacity is low, which is difficult to meet the demand of high energy density.

[0035] Therefore, the titanium-based composite negative electrode material is provided by the application, which is composed of Y2Ti2O7 and LiYTiO4; wherein the mass percentage of Y2Ti2O7 is 5% to 25%. The lithium intercalation potential of the titanium-based composite negative electrode material is 0.1V to 0.3V vs. Li + / Li, which is significantly lower than the lithium intercalation potential of the existing titanium-based material, thereby effectively improving the single cell voltage of the full battery; at the same time, the specific capacity of the titanium-based composite negative electrode material is greater than or equal to 200mAh / g, which is higher than that of the existing titanium-based material (for example, the specific capacity of lithium titanate material is about 175mAh / g). The reduction of lithium intercalation potential and the improvement of specific capacity jointly contribute to significantly improving the energy density of the full battery. In addition, the titanium-based composite negative electrode material is composed of metal oxide material and is non-flammable, so its safety is also better than that of traditional graphite material.

[0036] The technical solutions of the application will be further described in detail below in combination with the drawings and examples.

[0037] The application provides a titanium-based composite negative electrode material, which is composed of Y2Ti2O7 and LiYTiO4; wherein the mass percentage of Y2Ti2O7 is 5% to 25%.

[0038] In the application, the formation of Y2Ti2O7 and LiYTiO4 composite phase can reduce the lithium intercalation potential of the titanium-based composite material and improve the specific capacity, thereby being beneficial to improving the energy density of the full battery. Specifically, Y2Ti2O7 and the main phase LiYTiO4 form a synergistic effect in structure and electrochemistry. On the one hand, there are mixed metal sites composed of Y 3+ and Ti 4+ in the titanium-based composite material, the ionic radius of Y 3+ is large and the electronegativity is low, and the introduction of Y 3+ can weaken the strength of Ti-O bond, so that when lithium ions are inserted, Ti 4+Reduced to Ti 3+ The energy barrier required for this process is lowered, thereby increasing the lithium intercalation potential of the entire titanium-based composite material from above 1.5V compared to traditional titanium-based materials. + / Li levels dropped significantly to 0.1V~0.3V vs. Li + / Li. On the other hand, the two-phase interface formed between the Y2Ti2O7 phase and the main LiYTiO4 phase in the composite material can serve as a fast lithium-ion migration channel, which helps lithium-ion diffusion, enhances ion conduction, and enables more active materials to be effectively utilized during charging and discharging, ultimately increasing the specific capacity of the titanium-based composite material to over 200 mAh / g.

[0039] Compared to existing titanium-based materials with high lithium intercalation potential and low specific capacity, the titanium-based composite anode material provided by this invention exhibits a significantly reduced lithium intercalation potential, i.e., the anode potential is lowered. The single-cell voltage (V) of the full cell... 全 ) by positive electrode potential (E 正 ) and negative electrode potential (E) 负 The difference between V and V determines: 全 =E 正 -E 负 When the positive electrode potential remains constant, a decrease in the negative electrode potential directly increases the single-cell voltage of the entire battery. Combined with the energy calculation formula (energy (Wh) = voltage (V) × capacity (Ah)), it can be seen that the energy of the entire battery is positively correlated with voltage and capacity. Therefore, the titanium-based composite negative electrode material of this invention can effectively and significantly improve the energy density of the entire battery by increasing the single-cell voltage and specific capacity.

[0040] To achieve optimal overall performance, the mass percentage of Y₂Ti₂O₇ needs to be controlled between 5% and 25%. When the mass percentage of Y₂Ti₂O₇ is below 5%, its weakening effect on Ti-O bonds and the interphase effect are insufficient. Conversely, when the mass percentage of Y₂Ti₂O₇ is above 25%, it may lead to insufficient LiYTiO₄ phase with higher electrochemical activity in the titanium-based composite anode material, thus affecting the overall specific capacity and consequently the energy density of the full cell.

[0041] In some embodiments, the titanium-based composite anode material is a crystalline, plate-like or aggregated particle with a particle size of 0.1 μm to 20 μm, preferably 0.2 μm to 10 μm. This optimizes the lithium-ion transport path and reduces side reactions caused by excessive specific surface area, making the full battery more suitable for rapid charge and discharge and improving its cycle stability. It should be noted that the present invention does not strictly limit the specific morphology and size of the titanium-based composite anode material, as long as it meets the conventional particle size requirements for lithium-ion battery anode material raw materials.

[0042] The present application can synthesize the titanium-based composite negative electrode material by a sol-gel method and a solid phase method, which will be described in detail below.

[0043] As shown in the drawings, the present application provides a sol-gel method for preparing the titanium-based composite negative electrode material. Figure 1 The preparation method avoids the generation of impurity phases with weak electrochemical activity such as Y2O3 and TiO2, and then through aging treatment, slow polycondensation reaction and structural rearrangement occur between Ti-containing and Y-containing colloidal particles, forming a three-dimensional network structure connected by metal-oxygen-metal bonds, shortening the distance between Ti-containing and Y-containing colloidal particles, and making sodium ions uniformly coated in the three-dimensional network structure, realizing uniform distribution of elements at atomic or molecular level scale. Then, high-temperature heat treatment at 900-1200°C (not including both end temperatures) is performed to obtain a NaYTiO4 / Y2Ti2O7 composite material. Subsequently, through a molten salt ion exchange reaction, lithium ions (Li + ) in LiNO3 selectively replace sodium ions (Na + ) in the NaYTiO4 lattice, and finally the target product LiYTiO4 / Y2Ti2O7 composite material is obtained. The sol-gel method specifically comprises the following steps:

[0044] Step 101, preparing a precursor: dissolving a soluble yttrium source, a soluble titanium source, and an acidic complexing agent in a solvent, adding a sodium-containing compound solution, adjusting the pH value to obtain a complex sol containing Na, Ti, and Y elements, and performing aging treatment on the complex sol to make Ti-containing and Y-containing colloidal particles undergo polycondensation reaction, forming a dry gel with a three-dimensional network structure; after natural cooling, the precursor is obtained by grinding.

[0045] In some embodiments, the molar ratio of the used soluble yttrium source to the soluble titanium source is 1:1. The soluble titanium source can be a titanium ester, such as tetraethyl titanate, tetrabutyl titanate, etc.; and the soluble yttrium source can be a soluble yttrium salt, such as yttrium nitrate, yttrium acetate, etc. In this embodiment, the soluble titanium source is tetrabutyl titanate, and the soluble yttrium source is yttrium nitrate hexahydrate.

[0046] The acidic complexing agent is used to form a negatively charged complex unit through complexation reaction with Ti 4+ and Y 3+ , and Na + is dissolved in the complex sol in the form of a free cation, which maintains the system electric neutrality through charge neutralization to ensure stability. The molar ratio of the used acidic complexing agent to the soluble titanium source is (8-10):1. In this embodiment, the acidic complexing agent can be citric acid, which contains multiple carboxyl groups (-COOH) in its molecular structure, and these groups can form coordination bonds with Ti 4+ and Y3+ The complexation reaction occurs to form a water-soluble metal complex which is stable in structure and soluble in the reaction system.

[0047] In some embodiments, the solvent is an alcohol solvent, for example, any one of ethanol, methanol, isopropanol, ethylene glycol. In this embodiment, the solvent is ethanol.

[0048] In some embodiments, in order to inhibit the generation of impurity phases in the subsequent high-temperature heat treatment step (step 102 described below), the molar ratio of sodium ions in the sodium-containing compound solution to titanium ions in the soluble titanium source is 1:1-1.5:1. During the subsequent high-temperature heat treatment process, Na element will be lost to a certain extent, and when the content of Na element is too low (i.e., the molar ratio of sodium ions to titanium ions is less than 1:1), it is not possible to ensure that there is enough Na element to form NaYTiO4 phase with Y element and Ti element, resulting in partial Y element and Ti element forming undesired Y2O3, TiO2 and other impurity phases. However, when the content of Na element is too high (i.e., the molar ratio of sodium ions to titanium ions is greater than 1.5:1), the excess sodium element cannot be incorporated into the crystal lattice of NaYTiO4, and the remaining Na element will form non-active sodium compounds such as Na2O during the subsequent high-temperature heat treatment process, resulting in the need to increase the post-processing steps such as water washing, which is not conducive to production costs.

[0049] The sodium-containing compound is selected from any one or more of NaOH, Na2CO3, NaNO3, CH3COONa, and NaCl. In this embodiment, the sodium-containing compound solution is a NaOH solution.

[0050] In some embodiments, the pH value is 6.5-7.5. By adjusting the pH value, the coordination environment of Ti and Y elements is regulated to ensure that stable complexes are formed and non-target hydrolysis reactions to generate Y2O3, TiO2 and other impurity phases are avoided. 4+ , Y 3+ are easily hydrolyzed metal ions, and the degree of hydrolysis thereof is directly affected by the pH value. It has been found through experiments that when the pH value is too high or too low, the coordination balance between the acidic complexing agent and Ti 4+ , Y 3+ will be destroyed, causing them to separate from the complex state and undergo spontaneous hydrolysis, for example, Ti 4+ hydrolysis to form TiO2, and Y 3+ hydrolysis to form Y2O3, resulting in element separation and inability to achieve uniform mixing, which in turn makes it difficult to form NaYTiO4 and Y2Ti2O7 two phases during the subsequent high-temperature heat treatment.

[0051] The pH value of the solution can be adjusted by slowly adding ammonia water drop by drop to the solution. It is found by experiment that when the pH value is increased to about 4.0 at the initial stage of dropwise addition, a white gelatinous precipitate begins to form in the solution; when the pH value is increased to about 6.0 by continuing to add ammonia water, the precipitate begins to dissolve; and when the pH value is finally adjusted to about 7.0, a uniform and stable complex sol can be obtained.

[0052] In some embodiments, in the step 101, the soluble titanium source is dissolved in the solvent by dropwise addition, and stirring is performed simultaneously to avoid alcoholysis of the soluble titanium source. The sodium-containing compound solution is dissolved in the solvent by dropwise addition, and stirring is performed simultaneously to avoid the generation of a non-target product or the destruction of the stability of the sol (for example, the formation of agglomerates or precipitates) due to the generation of a local over-basic environment.

[0053] In some embodiments, the step 101 comprises:

[0054] In the step 1011, the complex sol is heated at 60-100°C to evaporate the solvent, thereby obtaining a pre-gel.

[0055] In some embodiments, the heating time in the step 1011 is 2-6 hours. After the treatment in the step 1011, the water and ethanol in the complex sol are evaporated.

[0056] In the step 1012, the pre-gel is heated at 100-200°C to perform aging treatment, so that a slow polycondensation reaction and structural rearrangement occur between the Ti-containing and Y-containing colloidal particles, thereby forming a dry gel having a three-dimensional network structure.

[0057] In some embodiments, the heating time in the step 1012 is 6-24 hours. During the aging process, a slow polycondensation reaction and structural rearrangement occur between the Ti-containing and Y-containing complex units (or colloidal particles) in the pre-gel. Specifically, the surfaces of the Ti-containing and Y-containing colloidal particles in the complex sol are adsorbed with water molecules, and thus are rich in active hydroxyl groups (Ti-OH and Y-OH). Under the heating and aging conditions at 100-200°C, the active hydroxyl groups on the surfaces of two adjacent colloidal particles undergo a dehydration reaction to release one molecule of water, and the remaining oxygen atoms form stable covalent bridge bonds (Ti-O-Ti, Y-O-Y or Ti-O-Y) with the Ti and Y atoms, so that the originally dispersed Ti-containing and Y-containing colloidal particles are gradually crosslinked to form a continuous and stable three-dimensional network structure. The Na + Na+ is wrapped in the three-dimensional network structure in the form of a free cation.

[0058] In the step 102, the precursor is subjected to high-temperature heat treatment to obtain a composite material of NaYTiO4 and Y2Ti2O7; and the temperature T1 of the high-temperature heat treatment is 900°C

[0059] The step 102 obtains a composite material composed of NaYTiO4 and Y2Ti2O7 by heat treating the precursor in a specific temperature range (900℃<T1<1200℃). The step 102 is based on the accurate control of the phase thermodynamic stability: in a relatively low temperature range (about 700℃ to 900℃), NaYTiO4 is the thermodynamically stable phase; and when the temperature rises above 1200℃, Y2Ti2O7 becomes the dominant thermodynamically stable phase. The present application performs heat treatment in 900℃<T1<1200℃, so that each element in the precursor can obtain sufficient energy for diffusion and crystallization, but it does not cause the complete decomposition of the NaYTiO4 phase or the single formation of the Y2Ti2O7 phase, thereby facilitating the simultaneous generation of the thermodynamically coexisting NaYTiO4 and Y2Ti2O7 phases, and laying a good foundation for the subsequent formation of the LiYTiO4 and Y2Ti2O7 composite material.

[0060] As the temperature T1 of the high-temperature heat treatment increases, the proportion of the Y2Ti2O7 phase in the composite material increases, and the proportion of the NaYTiO4 phase decreases. Preferably, the temperature T1 of the high-temperature heat treatment is 1000℃≤T1≤1100℃, so as to obtain the NaYTiO4 and Y2Ti2O7 phases with an optimal proportion relationship.

[0061] In some embodiments, the processing time of the step 102 is 1h-3h.

[0062] The step 103 ion-exchanges the NaYTiO4 and Y2Ti2O7 composite material with a lithium salt by a molten state ion exchange to obtain the titanium-based composite negative electrode material.

[0063] The ion exchange reaction in the step 103 aims to completely convert NaYTiO4 into LiYTiO4. In some embodiments, the step 103 comprises: ion-exchanging the NaYTiO4 and Y2Ti2O7 composite material with a lithium salt at 300℃-600℃ for 2h-6h, after natural cooling, adding distilled water for mixing and stirring, and performing centrifugal separation to obtain the titanium-based composite negative electrode material. In some embodiments, the lithium salt is selected from any one or more of Li2SO3, Li3PO4, Li2HPO4, LiH2PO4, Li2CO3, CH3COOLi, and LiNO3. In this embodiment, the lithium salt is LiNO3. Taking the lithium salt as LiNO3 as an example, the ion exchange reaction occurring in the step 103 is:

[0064] NaYTiO4+ LiNO3→LiYTiO4+NaNO3 Formula 1

[0065] It should be noted that in step 103, the lithium salt selectively undergoes ion exchange with NaYTiO4, but hardly reacts with Y2Ti2O7. NaYTiO4 has a distorted perovskite structure (or a perovskite-like structure), in which, due to Na… + With a relatively large radius (approximately 1.02 Å) and a low charge (+1), its lattice sites have weak binding energy, making it easily bound by other small-radius, like-charge ions (such as Li) under heating conditions. + The lattice sites of Y₂Ti₂O₇ are replaced by approximately 0.76 Å. In contrast, Y₂Ti₂O₇ has a pyrochlore structure, and its lattice sites are all replaced by Y₂Ti₂O₇. 3+ Ti 4+ Occupy, and Y 3+ Ti 4+ It forms strong bonds with oxygen ions. This structure is highly ordered and stable, and there are no suitable Li-ion bonds. + Replaced cation sites.

[0066] To ensure sufficient replacement of sodium ions in NaYTiO4, an excess of lithium ions is required, along with suitable temperature and time conditions to promote the complete execution of Formula 1. In some embodiments, the molar ratio of lithium ions in the lithium salt to sodium ions in the NaYTiO4 / Y2Ti2O7 composite material is 1.5:1 to 3:1 to ensure the forward execution of Formula 1.

[0067] like Figure 2 As shown, the present invention also provides a solid-state preparation method for titanium-based composite anode materials, comprising:

[0068] Step 201: Grind and mix yttrium oxide, titanium oxide and sodium salt, and heat to undergo solid-state synthesis reaction to obtain a composite material of NaYTiO4 and Y2Ti2O7; the heating temperature T2 is: 900℃ < T2 < 1200℃.

[0069] The stoichiometric ratio of the yttrium-containing oxide and the titanium-containing oxide used is 1:1, and the molar ratio of sodium ions in the sodium salt to titanium ions in the titanium-containing oxide is 1:1 to 1.5:1. The yttrium-containing oxide and the titanium-containing oxide are Y₂O₃ and TiO₂, respectively; the sodium salt is selected from any one or more of Na₂CO₃, CH₃COONa, NaNO₃, Na₂SO₃, Na₃PO₄, Na₂HPO₄, and NaH₂PO₄.

[0070] Taking Na₂CO₃ as an example, the solid-phase synthesis reaction includes the following reaction equation:

[0071] Na2CO3+ Y2O3+2TiO2→2 NaYTiO4+CO2 Formula 2

[0072] Y2O3 + 2TiO2→ Y2Ti2O7 Formula 3

[0073] As described above, the two phases of NaYTiO4 and Y2Ti2O7 can stably coexist in a specific temperature range of 900℃~1200℃ (not including both end temperatures). In this temperature range, Formula 2 and Formula 3 occur simultaneously, that is, the NaYTiO4 crystal phase and the Y2Ti2O7 crystal phase are formed at the same time, realizing the in-situ compounding of the NaYTiO4 phase and the Y2Ti2O7 phase. In contrast, when T2≤900℃, the product is only a single NaYTiO4 phase; when T2≥1200℃, the product is only a single Y2Ti2O7 phase.

[0074] In some embodiments, the processing time of step 201 is 6h~24h, and preferably, the temperature of step 201 is 1000℃~1100℃, and the processing time is 10h~12h.

[0075] In step 202, the NaYTiO4 / Y2Ti2O7 composite material is ion exchanged with a lithium salt by a molten state ion exchange method to obtain the titanium-based composite negative electrode material.

[0076] In the above formula, the molar ratio of lithium ions in the lithium salt to sodium ions in the NaYTiO4 / Y2Ti2O7 composite material (NaYTiO4 / Y2Ti2O7 composite material) is 1.5:1~3:1, so as to ensure that the ion exchange reaction proceeds in the forward direction. The lithium salt is selected from any one or more of Li2SO3, Li3PO4, Li2HPO4, LiH2PO4, Li2CO3, CH3COOLi, and LiNO3.

[0077] In step 202, the molten state ion exchange is to exchange the mixed powder obtained by grinding the NaYTiO4 / Y2Ti2O7 composite material and the lithium salt at 300℃~600℃ for 2h~6h. In the molten state ion exchange process, the lithium salt is heated to above its melting point, so that it changes from a solid state to a molten state, thereby improving the migration ability of Li + and increasing the contact area between the NaYTiO4 / Y2Ti2O7 composite material and Li + , promoting the ion exchange reaction, so that Na + in NaYTiO4 is replaced by Li + .

[0078] The technical solutions of the present application are further described in detail below in combination with embodiments.

[0079] Embodiment 1

[0080] The present embodiment provides a sol-gel method for preparing a titanium-based composite negative electrode material, which specifically comprises:

[0081] Step (1), tetrabutyl titanate was added dropwise into ethanol with stirring to avoid alcoholysis of tetrabutyl titanate. Then yttrium nitrate hexahydrate and citric acid were added, and the mixture was stirred to form solution A. The molar ratio of tetrabutyl titanate, yttrium nitrate hexahydrate and citric acid was 1:1:9.

[0082] Step (2), 5 mol / L NaOH solution was added dropwise into solution A with stirring to avoid the formation of non-target products or the destruction of sol stability (e.g., the formation of agglomerates or precipitates) due to the generation of local over-basing, to obtain solution B. The molar ratio of NaOH to tetrabutyl titanate in solution A was 1.25:1. The dropwise addition time was 1 min.

[0083] Step (3), solution B was heated to 60°C, and 1 mol / L ammonia water was slowly added dropwise into solution B while continuously stirring solution B. When the pH reached approximately 4.0, a large amount of sticky white gel-like precipitate was generated and heat was released. Stirring was continued and ammonia water was added dropwise until the pH reached approximately 6.0, at which point the white gel-like precipitate began to dissolve. Ammonia water was continuously added dropwise until the pH reached 7.0, to obtain a complex sol of Na, Ti, Y and ammonium (NH4 + ) dissolved therein.

[0084] Step (4), the complex sol was placed in a blast oven, and the heating temperature was set to 80°C for 12 h to evaporate the solvent, to obtain a pre-gel. The heating temperature was then increased to 140°C for 24 h to age the pre-gel, to obtain a dry gel. The dry gel was naturally cooled in an environment with a relative humidity of 40%, and after 1 h of cooling, the dry gel was ground into a powder using a planetary ball mill, to obtain a precursor of NaYTiO4 / Y2Ti2O7 composite oxide. The grinding method included: grinding for 3 min at a running speed of 400 rpm on the planetary ball mill, opening the ball mill jar to cool for 3 min, and repeating 3 times.

[0085] Step (5), the precursor was placed in an alumina crucible without a lid, and high-temperature heating was performed in an air atmosphere. The heating program was set as follows: the temperature was increased to 1100°C at a rate of 3°C / min from room temperature, and after maintaining the temperature at 1100°C for 60 min, the temperature was naturally decreased to room temperature, to obtain a NaYTiO4 / Y2Ti2O7 composite material.

[0086] Step (6), the NaYTiO4 / Y2Ti2O7 composite material was thoroughly mixed with LiNO3, and heating was performed in an alumina crucible in an air atmosphere. The Na + in the NaYTiO4 and the Li +The molar ratio of Na2CO3 to TiO2 is 1.3:1. The heating program is set as follows: increasing from room temperature to 900°C at a rate of 3°C / min, keeping at 900°C for 60 min, and then naturally cooling down to room temperature. The mixture in the crucible is taken out and mixed with distilled water. The volume ratio of distilled water to the mixture is 5:1. The obtained turbid solution is then centrifuged to obtain the insoluble solid. The centrifugal speed is 5000 rpm, and the centrifugal time is 5 min. Step (6) is repeated three times to obtain the LiYTiO4 / Y2Ti2O7 composite material.

[0087] The obtained LiYTiO4 / Y2Ti2O7 composite material is charged and discharged at a rate of 0.2C, and the obtained charge-discharge curve is shown in FIG. 2. Figure 3 From the curve characteristics, it can be seen that the charge-discharge curve is smooth in the voltage range of 0.1V-0.3V, indicating that the lithium intercalation potential range of the material is 0.1V-0.3V vs. Li + / Li; and the capacity span on the horizontal coordinate of the charge-discharge curve is more than 200 mAh / g, indicating that the specific capacity of the material is higher than 200 mAh / g, which is superior to traditional negative electrode materials.

[0088] Example 2

[0089] The difference between this example and Example 1 is that in step (5), the heating program is set as follows: increasing from room temperature to 1000°C at a rate of 3°C / min, keeping at 1000°C for 60 min, and then naturally cooling down to room temperature.

[0090] Comparative Example 1

[0091] In this comparative example, NaYTiO4 / Y2Ti2O7 composite material is prepared by using steps (1)-(5) of Example 1. The difference between steps (1)-(5) of this comparative example and Example 1 is that in step (5), the heating program is set as follows: increasing from room temperature to 900°C at a rate of 3°C / min, keeping at 900°C for 60 min, and then naturally cooling down to room temperature. Then, ion exchange is performed by using the same method as step (6) of Example 1.

[0092] Comparative Example 2

[0093] Y2O3, TiO2 and Na2CO3 are ground and mixed. The stoichiometric ratio of Y2O3 to TiO2 used is 1:1, and the molar ratio of Na in Na2CO3 to Ti in TiO2 is 1.3:1. Then, high-temperature heat treatment is performed. The heating program is set as follows: increasing from room temperature to 900°C at a rate of 3°C / min, keeping at 900°C for 60 min, and then naturally cooling down to room temperature. Then, ion exchange is performed by using the same method as step (6) of Example 1.

[0094] In this invention, the relative content ratio of LiYTiO4 to Y2Ti2O7 in the sample was determined using the external standard method. The specific experimental method was as follows: Pure Y2Ti2O7 and pure LiYTiO4 were weighed separately, and the mass percentage of pure Y2Ti2O7 in the pure Y2Ti2O7 / pure LiYTiO4 mixture was changed (5%, 10%, 15%, 20%) to prepare a series of standard samples. X-ray diffraction (XRD) tests were performed on each standard sample, and the intensity ratio of its main characteristic diffraction peaks was analyzed to establish a fitting curve of "mass ratio - peak intensity ratio". Subsequently, XRD tests were performed on the materials prepared in Examples 1, 2, Comparative Example 1, and Comparative Example 2. Based on the intensity ratio of the characteristic diffraction peaks of LiYTiO4 to Y2Ti2O7, combined with the above fitting curve, the relative mass ratio of Y2Ti2O7 to LiYTiO4 in the material was calculated, as shown in Table 1 below.

[0095] Table 1. Mass percentages of Y₂Ti₂O₇ and LiYTiO₄ in different titanium-based composite anode materials

[0096]

[0097] Figure 4 The XRD patterns of the materials obtained from Examples 1, 2, Comparative Example 1, and Comparative Example 2 are shown. Combined with... Figure 4 As shown in Table 1, the materials prepared in Examples 1 and 2 contain Y2Ti2O7, while no characteristic diffraction peaks of Y2Ti2O7 were observed in the XRD patterns of Comparative Examples 1 and 2. This indicates that Examples 1 and 2 successfully prepared titanium-based composite materials composed of two phases, LiYTiO4 and Y2Ti2O7, while the materials prepared in Comparative Examples 1 and 2 did not contain Y2Ti2O7, and only pure LiYTiO4 material was obtained. This proves that high-temperature heat treatment or solid-state synthesis reaction at 900℃ cannot obtain LiYTiO4 / Y2Ti2O7 composite materials, but when the high-temperature heat treatment temperature is 1000℃~1100℃, titanium-based composite materials composed of two phases, LiYTiO4 and Y2Ti2O7, can be obtained. Furthermore, when the high-temperature heat treatment temperature is 1100℃, compared with the high-temperature heat treatment temperature of 1000℃, a LiYTiO4 / Y2Ti2O7 composite material with a higher mass percentage of Y2Ti2O7 can be obtained.

[0098] Batteries from Examples 1, 2, Comparative Example 1, and 2 were fabricated and electrochemically tested using the following methods:

[0099] The prepared material was mixed with SuperP conductive agent and PVDF binder at a mass ratio of 6:2:2 and stirred thoroughly into a slurry, which was coated on a carbon-coated copper foil in an argon glove box with lithium metal sheet as the counter electrode. CR2025 separators were used to make button cells. The voltage range of charge-discharge test was 0.01V~3.0V vs. Li + / Li.

[0100] Table 2. First charge-discharge and cycle capacity performance of different titanium-based composite negative electrode materials.

[0101]

[0102] As can be seen from Table 2, the first discharge capacities of Example 1 (LiYTiO4 / Y2Ti2O7 composite material) and Example 2 (LiYTiO4 / Y2Ti2O7 composite material) are 410.6 mAh / g and 472.9 mAh / g, respectively, which are much higher than those of Comparative Example 1 (pure LiYTiO4 material) and Comparative Example 2 (pure LiYTiO4 material). It can be seen that the LiYTiO4 / Y2Ti2O7 composite material obtained by the method of the present application has a higher specific capacity, which is beneficial to improving the energy density of the negative electrode material. The capacities of Example 1 and Example 2 after 50 cycles are higher than those of Comparative Example 1 and Comparative Example 2, indicating that the addition of Y2Ti2O7 suppresses the cycle decay of LiYTiO4, and the structure stability of the LiYTiO4 / Y2Ti2O7 composite material obtained by the method of the present application is more excellent. Further, the first discharge capacity and the first charge capacity of Example 2 are both higher than those of Example 1, because in the titanium-based composite negative electrode material, LiYTiO4 is the electrochemically active phase, and a higher proportion can provide more lithium ion insertion sites, thereby directly contributing to a higher specific capacity. At the same time, the main function of Y2Ti2O7 is to weaken the Ti-O bond to reduce the lithium intercalation potential of the material, and to provide a fast migration channel for lithium ions through the interface formed with LiYTiO4. Although the Y2Ti2O7 content of 7.30% in Example 2 is lower than that in Example 1, it can still play a synergistic effect of the interface, effectively maintaining a low lithium intercalation potential while avoiding the problem of diluting the proportion of the electrochemically active phase by excessive Y2Ti2O7. Therefore, the optimization of the two-phase proportion makes Example 2 exhibit more superior comprehensive electrochemical performance.

[0103] In summary, the present application provides a titanium-based composite negative electrode material composed of Y2Ti2O7 and LiYTiO4, wherein the mass proportion of Y2Ti2O7 is 5% to 25%. The key advantage of this material is its low lithium intercalation potential (0.1V~0.3V vs. Li +The single cell voltage of the full battery can be improved due to the lower voltage of the material than the existing titanium-based material; and the specific capacity (≥200mAh / g) of the material is higher than that of the traditional material, which can greatly improve the energy density of the battery. In addition, the material is composed of metal oxide and does not contain flammable components, so the safety is better than that of graphite material. The application also provides two simple preparation methods of sol-gel method and solid phase method, and the relative proportion of the two phases in the material can be directly controlled by adjusting the temperature of the sintering crystallization or solid phase synthesis reaction step.

[0104] It should be noted that in this document, the terms "comprise", "comprising", or any other variant thereof are intended to cover a non-exclusive inclusion, so that a process, method, article, or apparatus that comprises a list of elements does not only include those elements, but also includes other elements not expressly listed or inherent to such process, method, article, or apparatus. Without more limitations, the element defined by the statement "comprises a" does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0105] Although the content of the application has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the application. After reading the above content, various modifications and alternatives of the application will be apparent to those skilled in the art. Therefore, the protection scope of the application should be defined by the appended claims.

Claims

1. A titanium-based composite negative material, suitable for lithium ion batteries, characterized in that, The titanium-based composite negative electrode material is composed of Y2Ti2O7 and LiYTiO4, and the Y2Ti2O7 and the LiYTiO4 are composite phases; the mass percentage of the Y2Ti2O7 is 5% to 25%; the titanium-based composite negative electrode material is prepared by using a sol-gel method, and the preparation method comprises the following steps: Step 1, preparing a precursor: dissolving a soluble yttrium source, a soluble titanium source and an acidic complexing agent in a solvent, adding a sodium compound solution, adjusting the pH value to obtain a complex sol containing Na, Ti and Y elements, and performing aging treatment on the complex sol to make the Ti-containing and Y-containing colloidal particles undergo polycondensation reaction to form a dry gel with a three-dimensional network structure; after natural cooling, the dry gel is ground to obtain the precursor; Step 2, high-temperature heat treatment of the precursor to obtain a composite material of NaYTiO4 and Y2Ti2O7; the temperature T1 of the high-temperature heat treatment is 900 DEG C < T1 < 1200 DEG C; Step 3, ion exchange of the composite material of NaYTiO4 and Y2Ti2O7 with a lithium salt by using a molten state ion exchange method to obtain the titanium-based composite negative electrode material.

2. The titanium-based composite anode material of claim 1, wherein, The mass percentage of the Y2Ti2O7 is 7% to 17.5%.

3. The titanium-based composite anode material of claim 1, wherein, In the step 1, the pH value is 6.5 to 7.

5.

4. The titanium-based composite anode material of claim 1, wherein, In the step 1, the molar ratio of sodium ions in the sodium compound solution to titanium ions in the titanium source is 1:1 to 1.5:1; and in the step 3, the molar ratio of lithium ions in the lithium salt to sodium ions in the composite material of NaYTiO4 and Y2Ti2O7 is 1.5:1 to 3:

1.

5. The titanium-based composite anode material of claim 1, wherein, The step 3 comprises: exchanging the composite material of NaYTiO4 and Y2Ti2O7 with the lithium salt at 300 DEG C to 600 DEG C for 2h to 6h, after natural cooling, adding distilled water for mixing and stirring, centrifugal separation is performed to obtain the titanium-based composite negative electrode material.

6. A titanium-based composite negative material suitable for use in lithium ion batteries, characterized in that, The titanium-based composite negative electrode material is composed of Y2Ti2O7 and LiYTiO4, and the Y2Ti2O7 and the LiYTiO4 are composite phases; the mass percentage of the Y2Ti2O7 is 5% to 25%; the titanium-based composite negative electrode material is prepared by using a sol-gel method, and the preparation method comprises the following steps: Step 1, grinding and mixing yttrium oxide, titanium oxide and a sodium salt, and heating to perform solid-phase synthesis reaction to obtain a composite material of NaYTiO4 and Y2Ti2O7; the temperature T2 of the heating is 900 DEG C < T2 < 1200 DEG C; Step 2, ion exchange of the composite material of NaYTiO4 and Y2Ti2O7 with a lithium salt by using a molten state ion exchange method to obtain the titanium-based composite negative electrode material.

7. The titanium-based composite anode material of claim 6, wherein, The mass percentage of the Y2Ti2O7 is 7% to 17.5%.

8. The titanium-based composite anode material of claim 6, wherein, In the step 1, the molar ratio of sodium ions in the sodium salt to titanium ions in the titanium oxide is 1:1 to 1.5:1; and in the step 2, the molar ratio of lithium ions in the lithium salt to sodium ions in the composite material of NaYTiO4 and Y2Ti2O7 is 1.5:1 to 3:

1.

9. The titanium-based composite anode material of claim 6, wherein, In the step 2, the molten state ion exchange is that the mixed powder obtained by grinding the composite material of NaYTiO4 and Y2Ti2O7 and a lithium salt is exchanged at 300 DEG C to 600 DEG C for 2 h to 6 h.

10. A lithium-ion battery, characterized by, The negative electrode made of the titanium-based composite negative electrode material as claimed in any one of claims 1 to 5 or any one of claims 6 to 9.

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