A lithium iron phosphate positive electrode material with titanium ion-induced iron lithium-titanium lithium heterogeneous phase construction and a preparation method thereof

Abstract

A lithium iron phosphate cathode material with titanium ion-induced heterogeneous construction of lithium iron-titanium lithium and its preparation method, which relates to lithium iron phosphate cathode materials and their preparation methods. It aims to solve the technical problem of low performance of existing modified lithium iron phosphate materials. The structural formula of the material in this invention is: LiFePO4 ·xLiTi2(PO4)3, where 0 < x < 0.011. The preparation method is as follows: First, prepare a lithium titanate precursor through steps such as a sintering aid lithium source, compaction, and presintering, which expands the formation window of lithium titanate and promotes the subsequent in-situ formation of heterogeneous lithium iron phosphate and lithium titanate, forming a well-structured, electrochemically active, and high-ion-conductivity lithium titanate heterogeneous phase. The discharge specific capacities of this material at 0.1C, 1C, and 10C reach 162 mAh / g, 149 mAh / g, and 110 mAh / g respectively, and the capacity retention rate reaches 98.3% after 1000 cycles at 1C. It can be used in the battery field.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery preparation, specifically relating to lithium iron phosphate cathode material and its preparation method. Background Technology

[0002] Lithium iron phosphate (LiFePO4) is a cathode material for lithium-ion batteries, boasting advantages such as low raw material cost, good safety, and long cycle life. However, its low electronic conductivity and slow ion migration rate severely limit the improvement of battery rate performance. Currently, methods to improve the defects of LiFePO4 cathode materials involve composite modification, introducing a highly conductive second phase, or constructing multidimensional ion transport channels. However, the composite process with highly conductive materials or fast ion conductors is mainly achieved through physical blending or in-situ composite, both of which have limitations. On the one hand, physical mixing typically only achieves simple macroscopic blending of components, with the conductive phase and active material often only in point contact or localized coating, resulting in poor dispersion uniformity and bonding tightness, which is detrimental to capacity retention during high-rate discharge and long-term cycling. On the other hand, while in-situ composite methods promise a tighter and more stable interfacial bond, the formation conditions of the second phase differ from those of the first phase, making it difficult to precisely control its purity and structural integrity during introduction. Therefore, conventional composite materials and methods have limited ability to improve the overall performance of materials, making it difficult to achieve synergistic optimization of electron transport and ion diffusion kinetics, and difficult to simultaneously meet the requirements of high rate capacity and long cycle life. Summary of the Invention

[0003] The present invention aims to solve the technical problem of low performance of existing modified lithium iron phosphate (LiFePO4) materials, and provides a lithium iron phosphate cathode material with titanium ion-induced lithium iron phosphate-titanium lithium heterogeneous structure and its preparation method.

[0004] The lithium iron phosphate cathode material constructed by titanium ion-induced lithium iron phosphate-lithium titanium-lithium heterostructure of the present invention has the structural formula LiFePO4 ·xLiTi2(PO4)3, wherein 0 <x<0.011。

[0005] The preparation method of the lithium iron phosphate cathode material constructed by titanium ion-induced lithium iron phosphate-lithium titanium-lithium heterostructure according to the present invention is carried out according to the following steps:

[0006] 1. The titanium source, lithium source, and phosphorus source are ball-milled and mixed according to the molar ratio of Li:Ti:P of 1:2:3, and the mixed raw material is compacted to obtain lithium titanium phosphate raw material.

[0007] 2. Place the lithium titanium phosphate raw material in a furnace and heat it to 200-400℃ at a heating rate of 5-10℃ / min, and hold it for 1-5 hours for pre-sintering to obtain the lithium titanium phosphate precursor.

[0008] 3. Iron phosphate, lithium source, carbon source and lithium titanium phosphate precursor are ball-milled and mixed to obtain a mixture; wherein the amount of titanium in the lithium titanium phosphate precursor is 0.6% to 2.2% of the amount of iron in the iron phosphate.

[0009] 4. Place the mixture in a furnace and calcine it at a heating rate of 5-10℃ / min to 500-800℃ for 6-13 hours under an inert gas environment to obtain a lithium iron phosphate cathode material with titanium ion-induced lithium iron phosphate-titanium lithium heterogeneous structure.

[0010] Furthermore, the titanium source mentioned in step one is one or more of titanium dioxide, titanium citrate, titanium oxysulfate, titanium tetrachloride, tetrabutyl titanate, and tetraisopropyl titanate.

[0011] Furthermore, the lithium source mentioned in step one is one or more of LiOH, Li4P2O7, Li2B4O7 and Li3PO4; these lithium sources all have a combustion-aiding effect, LiOH has a low melting point and high reactivity; Li4P2O7 and Li2B4O7 can greatly promote densification, and Li3PO4 has high chemical compatibility.

[0012] Furthermore, the phosphorus source mentioned in step one is one or a mixture of several of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

[0013] Furthermore, the ball milling described in step one is carried out for 1 to 3 hours under the conditions of a ball-to-material mass ratio of (10 to 20): 1 and a rotation speed of 600 to 1200 r / min. When the titanium source is solid, dry ball milling is used, and when the titanium source is liquid, wet ball milling is used, with anhydrous ethanol as the dispersant.

[0014] Furthermore, the compaction process described in step one involves maintaining the mixture under a pressure of 10-50 MPa for 5-10 minutes.

[0015] Furthermore, the lithium source mentioned in step three is one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium dihydrogen phosphate;

[0016] Furthermore, the amount of lithium source used in step three is measured according to the lithium-iron molar ratio, which is (1~1.03):1.

[0017] Furthermore, the carbon source mentioned in step three is one or more of glucose, sucrose, polyethylene glycol, and starch;

[0018] Furthermore, the amount of carbon source used in step three is measured according to the total mass of iron phosphate, lithium source, carbon source and lithium titanium phosphate precursor, with the amount of carbon source accounting for 8% to 15% of the total mass.

[0019] Furthermore, the ball milling described in step three is carried out at a ball-to-material ratio of (10-20):1 and a ball milling speed of 600-1200 r / min for 5-10 hours.

[0020] Furthermore, the inert atmosphere mentioned in step four is argon, nitrogen, or a mixture of hydrogen and argon.

[0021] The method of this invention can induce the formation of lithium titanium phosphate (LiTi2(PO4)3) material, requiring only a small amount of titanium to effectively generate lithium titanium phosphate (LiTi2(PO4)3), greatly improving the conversion efficiency of lithium titanium phosphate and enhancing its modification effect on lithium iron phosphate. The generated heterogeneous lithium titanium phosphate has a NASICON structure with three-dimensional ion channels, and its lithium-ion diffusion coefficient can reach 10. -6 ~10 -8 cm 2 / s, compared to lithium iron phosphate 10 -12 ~10 -14 cm 2 / The diffusion coefficient of s is six orders of magnitude higher. Therefore, the introduction of titanium ions not only improves the intrinsic electronic conductivity of the bulk lithium iron phosphate (LFP) phase, but the induced titanium lithium phosphate heterophase, acting as a high-speed ion conductor, also enhances the interfacial ion transport of LFP. The two synergistically construct a highly efficient electron-ion transport network, greatly enhancing the rate performance and cycle stability of LFP. The "lithium iron phosphate-lithium titanium lithium" two-phase composite structure, with its synergistic enhancement of the "bulk phase-interface" advantage, achieves a synergistic improvement in rate capacity and cycle life.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] (1) The technical solution of the present invention optimizes the raw materials, selects lithium sources that can reduce the sintering temperature and form a low-temperature liquid phase, enhances the mechanical contact between particles by compaction, shortens the material diffusion distance, and initially establishes the interparticle bonding through pre-sintering, providing a stable structural basis and promoting the subsequent simultaneous generation of lithium iron phosphate and lithium titanium phosphate. Under the combined effect of the three, the addition of a small amount (<2.2%) of lithium titanium phosphate precursor can effectively form a heterogeneous phase of lithium titanium phosphate with a well-structured structure, electrochemical activity and high ionic conductivity.

[0024] (2) The lithium iron phosphate cathode material prepared by this method with titanium ion induced lithium iron phosphate-lithium titanium phosphate heterostructure has greatly enhanced the rate performance and cycle stability of lithium iron phosphate due to the high stability and high ionic conductivity of lithium titanium phosphate. Its electrochemical performance can reach 0.1C discharge specific capacity ≥162mAh / g, 1C discharge specific capacity ≥149mAh / g, 10C discharge specific capacity ≥110mAh / g, and the capacity retention rate reaches 98.3% after 1000 cycles at 1C.

[0025] (3) The technical solution of the present invention only requires adjusting the amount of lithium titanium phosphate precursor added. During the sintering process of lithium iron phosphate, the original process does not need to be changed. The heterogeneous phase of lithium titanium phosphate can be constructed in situ by means of one-step heat treatment. The whole process does not require complex multi-step reactions, is simple to operate, has controllable cost, and is very easy to achieve large-scale manufacturing on existing production lines, thus realizing industrial production. Attached Figure Description

[0026] Figure 1 These are the XRD patterns of the lithium iron phosphate cathode materials prepared in Example 1 and Comparative Example 1.

[0027] Figure 2 This is a SEM image of the lithium iron phosphate cathode material prepared in Example 1.

[0028] Figure 3 This is the EDS image of the lithium iron phosphate cathode material prepared in Example 1.

[0029] Figure 4 The graph shows the cycling performance of the lithium iron phosphate materials prepared in Example 1 and Comparative Example 1 at 1C.

[0030] Figure 5 The graph shows the rate performance of the lithium iron phosphate cathode materials prepared in Example 1 and Comparative Example 1.

[0031] Figure 6 This is a graph showing the cycling performance of the lithium iron phosphate material prepared in Example 1 at 10C.

[0032] Figure 7 This is the CV curve of the lithium iron phosphate cathode material prepared in Example 1.

[0033] Figure 8 This is a graph showing the cycling performance of the lithium iron phosphate cathode material prepared in Example 2 at 1C.

[0034] Figure 9 This is the CV curve of the lithium iron phosphate cathode material prepared in Example 3.

[0035] Figure 10 This is the CV curve of the lithium iron phosphate cathode material prepared in Example 5. Detailed Implementation

[0036] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0037] Example 1: The preparation method of the lithium iron phosphate cathode material constructed by titanium ion-induced lithium iron phosphate-lithium titanium phase in this example is carried out according to the following steps:

[0038] 1. Weigh 2g of titanium dioxide, 0.3g of lithium hydroxide, and 4.32g of ammonium dihydrogen phosphate and add them to a ball mill jar. Ball mill for 3 hours at a ball-to-material mass ratio of 15:1 and a ball mill speed of 1000 r / min. Compact the mixed raw material under a pressure of 20 MPa for 5 minutes to obtain lithium titanium phosphate raw material.

[0039] 2. Place the lithium titanium phosphate raw material in a muffle furnace and heat it to 300°C at a heating rate of 5°C / min and hold it for 3 hours for pre-sintering to obtain the lithium titanium phosphate precursor.

[0040] 3. Add 10g of ferric phosphate, 2.45g of lithium carbonate, 0.62g of glucose, and 0.20g of lithium titanium phosphate precursor to a ball mill jar. Ball mill for 9 hours at a ball-to-material mass ratio of 15:1 and a ball mill speed of 1000 r / min to obtain a mixture. The amount of titanium in the lithium titanium phosphate precursor is 1.6% of the amount of iron in the ferric phosphate.

[0041] 4. The mixture is placed in a tube furnace and calcined at 650°C for 9 hours under an argon atmosphere at a heating rate of 5°C / min to obtain a lithium iron phosphate cathode material with a titanium ion-induced lithium iron phosphate-titanium lithium heterostructure, the structural expression of which is LiFePO4 ·0.008LiTi2(PO4)3.

[0042] Comparative Example 1: This comparative example is a lithium iron phosphate cathode material prepared without the addition of lithium titanium phosphate precursor. The specific preparation method is as follows:

[0043] 1. Weigh 10g of ferric phosphate, 2.45g of lithium carbonate and 0.62g of glucose and put them into a ball mill jar. Ball mill for 9 hours at a ball-to-material mass ratio of 15:1 and a ball mill speed of 1000 r / min to obtain a mixture.

[0044] 2. The mixture is placed in a tube furnace and heated to 650°C at a rate of 5°C / min under continuous argon gas supply for 9 hours to obtain lithium iron phosphate cathode material.

[0045] Comparative Example 2: This comparative example is a lithium iron phosphate cathode material without a pre-prepared lithium titanium phosphate precursor. This comparative example uses the same proportion of lithium titanium phosphate raw material as Example 1. The difference is that Comparative Example 2 only uses lithium carbonate as the lithium source, and the lithium titanium phosphate raw material is not pre-sintered but is mixed with the lithium iron phosphate raw material and then calcined. The specific preparation method is as follows:

[0046] 1. Weigh 10g of ferric phosphate, 2.47g of lithium carbonate, 0.62g of glucose, 0.08g of titanium dioxide and 0.072g of ammonium dihydrogen phosphate and put them into a ball mill jar. Ball mill for 9 hours at a ball-to-material mass ratio of 15:1 and a ball mill speed of 1000r / min to obtain a mixture.

[0047] 2. The mixture is placed in a tube furnace and heated to 650°C at a rate of 5°C / min under continuous argon gas supply for 9 hours to obtain lithium iron phosphate cathode material.

[0048] Figure 1 These are the XRD patterns of the lithium iron phosphate cathode material prepared in Example 1 with a titanium ion-induced lithium iron phosphate-lithium titanium-lithium heterostructure and the lithium iron phosphate cathode material prepared in Comparative Example 1. Figure 1 It can be seen that the samples of Example 1 and Comparative Example 1 both exhibit the characteristic diffraction peaks of lithium iron phosphate (LiFePO4).

[0049] Figure 2 The image shows the SEM image of the lithium iron phosphate cathode material prepared by titanium ion-induced lithium iron phosphate-lithium titanium phosphate heterostructure. It shows that the introduction of lithium titanium phosphate did not have a significant impact on the morphology and particle size distribution of lithium iron phosphate particles, which is consistent with the morphological characteristics of lithium iron phosphate prepared by carbothermal reduction.

[0050] Figure 3 The image shows the EDS diagram of the lithium iron phosphate cathode material prepared in Example 1, which shows that titanium is uniformly distributed.

[0051] The lithium iron phosphate cathode material constructed by titanium ion-induced lithium iron phosphate-lithium titanium phosphate heterogeneous phase prepared in Example 1 and the lithium iron phosphate cathode material prepared in Comparative Example 1 were used as active materials, Super P as a conductive agent, and PVDF as a binder. The resulting slurry was coated on aluminum foil at a mass ratio of 8:1:1. After drying, it was cut into cathode sheets with a diameter of 14 mm and assembled into half-cells for charge-discharge testing.

[0052] The cycling performance of the lithium iron phosphate cathode material prepared in Example 1 (constructed by titanium ion-induced lithium iron phosphate-lithium titanium phase) and the lithium iron phosphate cathode material prepared in Comparative Example 1 at 1C is shown in the figure. Figure 4 As shown, the rate performance diagram is as follows: Figure 5 As shown. From Figure 4 and Figure 5As can be seen, the lithium iron phosphate cathode material constructed by titanium ion-induced lithium iron phosphate-lithium titanium phase in Example 1 achieved a maximum discharge specific capacity of 149.75 mAh / g at 1C rate, an average discharge specific capacity of 148.03 mAh / g after 1000 cycles, and a capacity retention rate of 98.3%; the discharge specific capacity at 10C rate was 112.9 mAh / g. The lithium iron phosphate material of Comparative Example 1 had a discharge specific capacity of 141.46 mAh / g at 1C rate, a capacity retention rate of 91.97% after 1000 cycles, and a discharge specific capacity of 87.42 mAh / g at 10C rate. Compared to Comparative Example 1, the discharge specific capacity and cycle stability of the lithium iron phosphate cathode material constructed by titanium ion-induced lithium iron phosphate-lithium titanium phase in Example 1 were significantly improved.

[0053] The rate performance of the lithium iron phosphate cathode material prepared in Comparative Example 2 is also plotted in... Figure 5 From Figure 5 As can be seen, the discharge specific capacity of the lithium iron phosphate cathode material prepared in Comparative Example 2 at a 10C rate is 97.76 mAh / g. The performance of the lithium iron phosphate material prepared by this method is worse than that of Comparative Example 1 without the addition of lithium titanium phosphate, but not as good as that of Example 1, which prepared a lithium titanium phosphate precursor through pre-sintering. This indicates that preparing a lithium titanium phosphate precursor through pre-sintering and other steps can promote the subsequent sintering of lithium titanium phosphate as a high-quality ion conductor, thereby greatly improving the rate performance of lithium iron phosphate.

[0054] The cycling performance of the lithium iron phosphate cathode material prepared in Example 1, which is a titanium ion-induced lithium iron phosphate-lithium titanium-lithium heterogeneous structure, is shown in the figure at 10C. Figure 6 As shown, from Figure 6 It can be seen that the material has an average discharge specific capacity of 108.85 mAh / g after 1000 cycles at 10C, and the capacity retention rate reaches 91.07%.

[0055] The CV curve of the lithium iron phosphate cathode material prepared in Example 1, which is a titanium ion-induced lithium iron phosphate-titanium lithium heterogeneous structure, is shown in the figure below. Figure 7 As shown, from Figure 7 It can be seen that the peak at 3.57 / 3.30V belongs to the redox peak of lithium iron phosphate material, and three redox peaks appear near 2.82 / 2.79V, 2.42 / 2.40V and 2.31 / 2.29V. Among them, the peak at 2.82 / 2.79V belongs to lithium titanium phosphate material, and the peaks at 2.42 / 2.40V and 2.31 / 2.29V belong to titanium pyrophosphate material.

[0056] Example 2: This example differs from Example 1 in that step three is replaced by the following operation:

[0057] 3. Add 10g of iron phosphate, 2.45g of lithium carbonate, 0.62g of glucose and 0.15g of lithium titanium phosphate precursor to a ball mill jar, and ball mill for 9 hours at a ball-to-material mass ratio of 15:1 and a ball mill speed of 1000 r / min to obtain a mixture; wherein the amount of titanium in the lithium titanium phosphate precursor is 1.2% of the amount of iron in the iron phosphate; other steps and parameters are the same as in Example 1, and the structural expression of the titanium ion-induced lithium iron phosphate-lithium titanium phosphate heterogeneous construction lithium iron phosphate cathode material is LiFePO4·0.006LiTi2(PO4)3.

[0058] Figure 8 This is a cycling performance diagram at 1C for the lithium iron phosphate cathode material prepared in Example 2, which is a titanium ion-induced lithium iron phosphate-lithium titanium-lithium heterostructure. Figure 2 It can be seen that the lithium iron phosphate material in Example 2 has a discharge specific capacity of up to 147.03 mAh / g at 1C rate, and a capacity retention rate of 98.4% after 1000 cycles.

[0059] Example 3: This example differs from Example 1 in that step three is replaced by the following operation: 10g of iron phosphate, 2.45g of lithium carbonate, 0.62g of glucose and 0.28g of lithium titanium phosphate precursor are added to a ball mill jar and ball milled for 9 hours at a ball-to-material mass ratio of 15:1 and a ball mill speed of 1000 r / min to obtain a mixture; wherein the amount of titanium in the lithium titanium phosphate precursor is 2.2% of the amount of iron in the iron phosphate; other steps and parameters are the same as in Example 1, and the structural expression of the titanium ion-induced lithium iron phosphate-lithium titanium phosphate heterogeneous construction lithium iron phosphate cathode material is LiFePO4 ·0.011LiTi2(PO4)3.

[0060] Figure 9 This is the CV curve of the lithium iron phosphate cathode material prepared in Example 3, which is a titanium ion-induced lithium iron phosphate-titanium lithium heterogeneous structure. Figure 9 It can be seen that the lithium iron phosphate material in Example 3 achieves a discharge specific capacity of 147.66 mAh / g at a 1C rate. From... Figure 9 Redox peaks can also be observed in lithium iron phosphate and lithium titanium phosphate materials.

[0061] Example 4: This example differs from Example 1 in that step three is replaced by the following operation: 10g of iron phosphate, 2.45g of lithium carbonate, 0.62g of glucose and 0.32g of lithium titanium phosphate precursor are added to a ball mill jar and ball milled for 9 hours at a ball-to-material mass ratio of 15:1 and a ball mill speed of 1000 r / min to obtain a mixture; wherein the amount of titanium in the lithium titanium phosphate precursor is 2.5% of the amount of iron in the iron phosphate; other steps and parameters are the same as in Example 1, and the structural expression of the titanium ion-induced lithium iron phosphate-lithium titanium phosphate heterogeneous construction lithium iron phosphate cathode material is LiFePO4 ·0.0125LiTi2(PO4)3.

[0062] The lithium iron phosphate cathode material prepared in Example 4, which is a titanium ion-induced lithium iron phosphate-lithium titanium phosphate heterogeneous structure, achieved a discharge specific capacity of 142.96 mAh / g at a 1C rate. This indicates that when the amount of lithium titanium phosphate precursor added is 2.5%, the performance of lithium iron phosphate begins to decline significantly. Furthermore, when the addition amount exceeds 2.2%, the effective conversion rate of lithium titanium phosphate decreases, occupying space in the active material and leading to a decline in the performance of lithium iron phosphate.

[0063] Example 5: This example differs from Example 1 in that step three is replaced by the following operation: 10g of iron phosphate, 2.45g of lithium carbonate, 0.62g of glucose and 0.08g of lithium titanium phosphate precursor are added to a ball mill jar and ball milled for 9 hours at a ball-to-material mass ratio of 15:1 and a ball mill speed of 1000 r / min to obtain a mixture; wherein the amount of titanium in the lithium titanium phosphate precursor is 0.6% of the amount of iron in the iron phosphate; other steps and parameters are the same as in Example 1, and the structural expression of the titanium ion-induced lithium iron phosphate-lithium titanium phosphate heterogeneous phase structure is LiFePO4 ·0.003LiTi2(PO4)3.

[0064] Figure 10 This is the CV curve of the lithium iron phosphate cathode material prepared in Example 5, which is a titanium ion-induced lithium iron phosphate-titanium lithium heterogeneous structure. From... Figure 10 As can be seen, in Example 5, the amount of lithium titanium phosphate precursor added was 0.6%. A redox peak of lithium titanium phosphate material appeared at around 2.8V, but the peak area was small, indicating that the presence of lithium titanium phosphate material was just detected when the titanium addition amount was 0.6%. The lithium iron phosphate cathode material prepared in Example 5 had a discharge specific capacity of 142.25 mAh / g at 1C.

[0065] Example 6: This example differs from Example 1 in that step three is replaced by the following operation: 10g of iron phosphate, 2.45g of lithium carbonate, 0.62g of glucose and 0.06g of lithium titanium phosphate precursor are added to a ball mill jar and ball milled for 9 hours at a ball-to-material mass ratio of 15:1 and a ball mill speed of 1000 r / min to obtain a mixture; wherein the amount of titanium in the lithium titanium phosphate precursor is 0.5% of the amount of iron in the iron phosphate; other steps and parameters are the same as in Example 1, and the structural expression of the titanium ion-induced lithium iron phosphate-lithium titanium phosphate heterogeneous construction lithium iron phosphate cathode material is LiFePO4 ·0.0025LiTi2(PO4)3.

[0066] In Example 6, the amount of lithium titanium phosphate precursor added was 0.5%. At this amount, no lithium titanium phosphate material was detected. The material prepared in Example 6 had a discharge specific capacity of 141.91 mAh / g at 1C.

[0067] This invention prepares lithium titanium phosphate precursors through pre-sintering, ultimately producing lithium iron phosphate cathode materials with a titanium ion-induced lithium iron phosphate-lithium titanium phosphate heterogeneous phase structure, achieving a dual improvement in rate capacity and cycle life. Under the same sintering regime, lithium titanium phosphate has a narrower formation window and weaker reaction kinetics than lithium iron phosphate. Therefore, conventional methods often require 3% to 5% titanium to generate lithium titanium phosphate. This method, however, compensates for the kinetic deficiencies in lithium titanium phosphate formation through the combined effects of sintering aids, compaction, and pre-sintering, promoting the subsequent in-situ one-step formation of lithium iron phosphate and lithium titanium phosphate. Adding a small amount of lithium titanium phosphate precursor is sufficient to fully utilize the effect of lithium titanium phosphate, significantly improving raw material conversion efficiency. The formation of the lithium titanium phosphate heterogeneous phase and the resulting performance improvement are not monotonically dependent on titanium content. When the amount of lithium titanium phosphate precursor added is less than 0.6%, the heterogeneous phase of lithium titanium phosphate does not appear; the conversion efficiency of lithium titanium phosphate is highest when the addition amount is 1.3%~1.6%, and the optimization effect on the performance of lithium iron phosphate is the best; when the addition amount is 2.5%, the conversion efficiency of lithium titanium phosphate decreases significantly, as the excess precursor is converted into a heterogeneous phase, which occupies the space of the active material and leads to a decline in performance. The lithium iron phosphate cathode material constructed by titanium ion-induced lithium iron phosphate-lithium titanium phosphate heterogeneous phase prepared by this invention exhibits excellent specific capacity at different discharge rates, and at the same time has extremely high capacity retention during long-term cycling.

Claims

1. A lithium iron phosphate cathode material with a titanium ion-induced lithium iron phosphate-titanium lithium heterogeneous structure, characterized in that, The structural formula of this material is LiFePO4·xLiTi2(PO4)3, where 0 <x<0.011。 2. A method for preparing a lithium iron phosphate cathode material with a titanium ion-induced lithium iron phosphate-titanium lithium heterogeneous phase structure as described in claim 1, characterized in that, This method is performed in the following steps:

1. The titanium source, lithium source, and phosphorus source are ball-milled and mixed according to the molar ratio of Li:Ti:P of 1:2:3, and the mixed raw material is compacted to obtain lithium titanium phosphate raw material.

2. Place the lithium titanium phosphate raw material in a furnace and heat it to 200-400℃ at a heating rate of 5-10℃ / min, and hold it for 1-5 hours for pre-sintering to obtain the lithium titanium phosphate precursor.

3. Iron phosphate, lithium source, carbon source and lithium titanium phosphate precursor are ball-milled and mixed to obtain a mixture; wherein the amount of titanium in the lithium titanium phosphate precursor is 0.6% to 2.2% of the amount of iron in the iron phosphate.

4. Place the mixture in a furnace and calcine it at a heating rate of 5-10℃ / min to 500-800℃ for 6-13 hours under an inert gas environment to obtain a lithium iron phosphate cathode material with titanium ion-induced lithium iron phosphate-titanium lithium heterogeneous structure.

3. The method for preparing a lithium iron phosphate cathode material with titanium ion-induced lithium iron phosphate-titanium lithium heterogeneous phase structure according to claim 2, characterized in that, Furthermore, the titanium source mentioned in step one is one or more of titanium dioxide, titanium citrate, titanium oxysulfate, titanium tetrachloride, tetrabutyl titanate, and tetraisopropyl titanate.

4. The method for preparing a lithium iron phosphate cathode material with titanium ion-induced lithium iron phosphate-titanium lithium heterogeneous structure according to claim 2 or 3, characterized in that, The lithium source mentioned in step one is one or more of LiOH, Li4P2O7, Li2B4O7 and Li3PO4.

5. A method for preparing a lithium iron phosphate cathode material with titanium ion-induced lithium iron phosphate-titanium lithium heterogeneous structure according to claim 2 or 3, characterized in that, The phosphorus source mentioned in step one is one or a mixture of several of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

6. A method for preparing a lithium iron phosphate cathode material with titanium ion-induced lithium iron phosphate-titanium lithium heterogeneous structure according to claim 2 or 3, characterized in that, The lithium source mentioned in step three is one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium dihydrogen phosphate.

7. A method for preparing a lithium iron phosphate cathode material with titanium ion-induced lithium iron phosphate-titanium lithium heterogeneous structure according to claim 2 or 3, characterized in that, The amount of lithium source used in step three is measured according to the lithium-iron molar ratio, which is (1~1.03):

1.

8. A method for preparing a lithium iron phosphate cathode material with titanium ion-induced lithium iron phosphate-titanium lithium heterogeneous structure according to claim 2 or 3, characterized in that, The carbon source mentioned in step three is one or more of glucose, sucrose, polyethylene glycol, and starch.

9. A method for preparing a lithium iron phosphate cathode material with titanium ion-induced lithium iron phosphate-titanium lithium heterogeneous structure according to claim 2 or 3, characterized in that, The amount of carbon source used in step three is measured by the total mass of iron phosphate, lithium source, carbon source and lithium titanium phosphate precursor, with the amount of carbon source accounting for 8% to 15% of the total mass.

10. A method for preparing a lithium iron phosphate cathode material with titanium ion-induced lithium iron phosphate-titanium lithium heterogeneous structure according to claim 2 or 3, characterized in that, The ball milling described in step three is performed at a ball-to-material ratio of (10-20):1 and a ball milling speed of 600-1200 r / min for 5-10 hours.

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