A long-cycle lithium-rich ruthenium-based cathode material with morphology controlled by high-energy ball milling and its preparation method

Abstract

A long-cycle lithium-rich ruthenium-based cathode material with morphology controlled by high-energy ball milling and a preparation method thereof, which relates to a lithium-rich ruthenium-based cathode material and a preparation method thereof. It aims to solve the technical problem of poor long-cycle stability of existing Li2RuO3 materials. The chemical expression of the long-cycle lithium-rich ruthenium-based cathode material of the present invention is Li2Ru 1‑x‑y Ti x Cr y O3, where x = y = 0.0375-0.125. Preparation method: Li2CO3, RuO2, TiO2, and Cr2O3 powders are subjected to high-energy ball milling to control the particle morphology to obtain a mixed powder. The mixed powder is then calcined to obtain a long-cycle lithium-rich ruthenium-based cathode material with morphology controlled by high-energy ball milling. The long-cycle lithium-rich ruthenium-based cathode material of the present invention exhibits a capacity retention rate of 95.8% to 98.7% after 300 cycles at 0.5C. The preparation method is simple and can be used in the lithium battery field.

Description

Technical Field

[0001] The invention relates to a lithium-rich ruthenium-based positive electrode material and a preparation method thereof, and belongs to the field of lithium battery positive electrode material preparation. Background Art

[0002] For typical LiTMO2 series layered materials, if one-third of the metal elements in the transition metal layer are replaced with lithium ions, Li2MO3 series materials can be obtained. Therefore, another way to express the molecular formula of Li2TMO3 material is Li(Li 1 / 3TM 2 / 3 )O2. The lithium ions in the transition metal layer are surrounded by 6 transition metal ions, forming a honeycomb structure, which reduces the symmetry of the material and causes the Li2TMO3 structural materials to be monoclinic. According to the different transition metal types, the space group of Li2TMO3 also has certain differences: C2 / c (M=Ru, Ti, Zr), C2 / m (M=Mn, Sn, Ir, Rh), etc. Li2RuO3, as a member of the Li2MO3 structural material, is a good electrode material for lithium ion insertion / extraction. Li2RuO3 is a layered structure composed of a lithium ion layer and a transition metal layer. The space group is C2 / c with monoclinic symmetry. Its experimental lattice parameter ( α=90°,β=100.073°,γ=90°) was reported by Kobayashi et al. The Li in the lithium layer occupies the 4e(0,y,1 / 4) position, and the transition metal layer is composed of 1 / 3Li + and 2 / 3Ru 4+ Composition, Li and Ru occupy the positions of 4d (1 / 4, 1 / 4, 1 / 2) and 8f (x, y, z) respectively, a Li + With 6 Ru 4+ Forming a honeycomb superlattice structure of LiRu6, the adjacent Ru 4+ The ions are linked by metallic bonds, but due to the dimerization of Ru, the Ru-Ru bond lengths are unequal. Both Li and Ru ions form octahedral structures with oxygen ions and occupy the center of the octahedron. Adjacent octahedra are connected to each other in a shared edge manner. These excess lithium ions in the Li2RuO3 positive electrode material can form a unique cationic configuration, arranged in a honeycomb shape, which is called a "superlattice structure". It is this unique "superlattice structure" that gives the Li2RuO3 material a stable structure during the charge and discharge process. In order to explore its discharge capacity, the Thackeray research group adjusted the electrochemical voltage range of the Li2RuO3 material to 2.8~4.6V, and the initial charge capacity was increased to 310mAh g -1, corresponding to 94% of lithium ions being extracted from the crystal structure, which means that all lithium ions, including those in the transition metal layer, can participate in the electrochemical reaction. However, the initial discharge capacity is only 245 mAh g -1 , 15% of the lithium ions cannot be reinserted into the layered structure. Not only is the initial coulombic efficiency low, but after only 20 cycles, the reversible specific capacity is only 190 mAh g -1 , the cyclic stability is poor. Summary of the Invention

[0003] The present invention aims to solve the technical problem of poor long-cycle stability of existing Li2RuO3 materials, and provide a long-cycle lithium-rich ruthenium-based positive electrode material and a preparation method thereof based on high-energy ball milling to control the morphology. This method introduces two elements, titanium and chromium, to modify the lithium-rich ruthenium-based positive electrode material through high-energy ball milling to control the morphology, thereby improving its electrochemical performance and cycle performance.

[0004] The chemical expression of the long-cycle lithium-rich ruthenium-based cathode material based on high-energy ball milling to control morphology is Li2Ru 1-x-y Ti x Cr y O3, where x=y=0.0375~0.125.

[0005] The above-mentioned method for preparing a long-cycle lithium-rich ruthenium-based cathode material with morphology controlled by high-energy ball milling is carried out according to the following steps:

[0006] 1. According to the mass ratio of Li2CO3, RuO2, TiO2 and Cr2O3 powders being 1:(1.23-1.67):(0.04-0.14):(0.04-0.13), Li2CO3, RuO2, TiO2 and Cr2O3 powders were weighed, mixed and added into a high-energy ball mill, and ball milled at a speed of 280-320 rpm for 2.8-3.2 hours to obtain a mixed powder;

[0007] 2. Place the mixed powder in a high-temperature furnace and calcine it at 950-1050°C in an oxygen environment for 14-16 hours to obtain a long-cycle lithium-rich ruthenium-based positive electrode material with morphology controlled by high-energy ball milling.

[0008] Furthermore, in step 1, the mass ratio of Li2CO3, RuO2, TiO2, and Cr2O3 powders is 1:(1.35-1.51):(0.04-0.14):(0.04-0.13). Li is lost during the calcination process, so excess Li2CO3 is added to compensate for the Li lost during the calcination process.

[0009] Furthermore, the calcination temperature in step 2 is 1000° C. and the calcination time is 15 hours.

[0010] Compared to existing lithium-ruthenium-rich Li2RuO3, the present invention's long-cycle lithium-ruthenium-rich cathode material, which uses high-energy ball milling to control morphology, introduces titanium and chromium into the traditional lithium-ruthenium-rich Li2RuO3. The selection of titanium, which has a stronger metal-oxygen bonding ability, helps stabilize the crystal structure and improve the material's stability. The selection of chromium, which has a similar atomic radius to ruthenium, allows for the combined action of titanium and chromium, increasing capacity while avoiding significant changes in the crystal structure, thereby improving the capacity and long-cycle stability of the cathode material. The capacity retention rate of the present invention's lithium-ruthenium-rich cathode material after 300 cycles at 0.5C increases from 67.7% to 95.8% to 98.7%.

[0011] The preparation method of the lithium-rich ruthenium-based positive electrode material of the present invention firstly controls the rotation speed and time of high-energy ball milling to achieve the purpose of sample crushing, mixing and alloying under appropriate grinding efficiency and grinding intensity, thereby obtaining LRTCO (Li2Ru) with a more regular shape and a more uniform particle size distribution. 1-x-y Ti x Cr y O3), and then regulating the high-temperature calcination conditions in an oxygen environment to obtain the best-performing lithium-rich ruthenium-based cathode material. This simple method can be used in the field of lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The Li2RuO3 prepared in Comparative Example 1 and the Li2Ru prepared in Example 1 0.925 Ti 0.0375 Cr 0.0375 XRD spectrum of O3;

[0013] Figure 2 is a SEM image of Li2RuO3 prepared in Comparative Example 1;

[0014] Figure 3 Li2Ru prepared in Example 1 0.925 Ti 0.0375 Cr 0.0375 SEM image of O3;

[0015] Figure 4 Li2Ru prepared in Example 1 0.925 Ti 0.0375 Cr 0.0375 O3 and the cycle performance curve of Li2RuO3 prepared in comparative example 1. DETAILED DESCRIPTION

[0016] The present invention is further described below with reference to the accompanying drawings and examples, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the invention shall be included in the scope of protection of the present invention. The preparation method of the novel lithium-rich ruthenium-based positive electrode material of the present invention is described in detail below through specific examples.

[0017] Example 1: The preparation method of the long-cycle lithium-rich ruthenium-based cathode material based on high-energy ball milling to control the morphology of this embodiment is carried out according to the following steps:

[0018] 1. Weigh 0.005232 mol (0.3866 g) of Li2CO3, 0.004400 mol (0.5856 g) of RuO2, 0.0001784 mol (0.01425 g) of TiO2, and 0.00008922 mol (0.01356 g) of Cr2O3 powder, mix them, and add them into a high-energy ball mill with agate balls and a ball-to-material mass ratio of 20:1. Ball milling is carried out at a speed of 300 rpm for 3 hours to obtain a mixed powder;

[0019] Second, the mixed powder was placed in a high-temperature furnace and calcined at 1000 ° C in an oxygen environment for 15 hours to obtain a long-cycle lithium-rich ruthenium-based cathode material with morphology controlled by high-energy ball milling. Its expression is Li2Ru 0.925 Ti 0.0375 Cr 0.0375 O3.

[0020] Comparative Example 1: This comparative example is to prepare a lithium-rich ruthenium-based positive electrode material Li2RuO3 positive electrode material. The specific preparation method is as follows:

[0021] 1. Weigh 0.005143 mol (0.38 g) of Li2CO3 powder and 0.004658 mol (0.62 g) of RuO2 powder, mix them, and add them to a high-energy ball mill. The ball milling beads are made of agate balls, and the ball-to-material mass ratio is 20:1. Ball milling is carried out at a speed of 300 rpm for 3 hours to obtain a mixed powder.

[0022] 2. The mixed powder is placed in a high-temperature furnace and calcined in air at 1000°C for 15 hours to obtain a lithium-rich ruthenium-based positive electrode material, the expression of which is Li2RuO3.

[0023] Li2RuO3 prepared in Comparative Example 1 and Li2Ru prepared in Example 1 0.925 Ti 0.0375 Cr 0.0375 O3 was tested by XRD, and the obtained XRD spectrum was as follows Figure 1 As shown, from Figure 1It can be seen that the prepared samples have good crystallinity and layered structure, and according to the main peak offset direction, it can be seen that the long-cycle lithium-rich ruthenium-based cathode material with morphology controlled by high-energy ball milling has a smaller interplanar spacing, indicating that the role of the metal valence bonds Ti-O and Ru-O in the lithium-rich ruthenium-based cathode material is further enhanced. 0.925 Ti 0.0375 Cr 0.0375 O3 was subjected to SEM testing, and the SEM photograph of Li2RuO3 prepared in Comparative Example 1 is shown in FIG. Figure 2 As shown, Li2Ru prepared in Example 1 0.925 Ti 0.0375 Cr 0.0375 The scanning electron microscope photo of O3 is as follows Figure 3 As shown, from Figure 2 、 3 It can be seen that the primary particle size of the sample of Example 1 is smaller than that of the sample of Comparative Example 1, the shape is more regular, the surface is smoother, and the particle size distribution is more uniform. The regular shape makes the diffusion length equal, which helps to achieve uniform lithium ion insertion and deinsertion; the smooth surface is conducive to further reducing the side reaction with the electrolyte, and the smaller particle size is conducive to the infiltration of the electrolyte and Li + Diffusion, and a proper reduction in the primary particle size will reduce Li + The diffusion path gives the material better discharge capacity and rate performance.

[0024] The long-cycle lithium-rich ruthenium-based positive electrode material with morphology controlled by high-energy ball milling obtained in Example 1 and the lithium-rich ruthenium-based positive electrode material prepared in Comparative Example 1 were used as electrode active materials for electrochemical testing. The assembly steps of the battery were as follows: the electrode active material, the conductive agent Super P, and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 8:1:1, mixed in a mortar and transferred to a weighing bottle. Subsequently, an appropriate amount of N-methylpyrrolidone (NMP) was added to the weighing bottle. After the solid-liquid mixture in the bottle became viscous, a magnet was added and magnetically stirred at room temperature for 6 hours to obtain a viscous but fluid electrode paste. The electrode paste was scraped onto the electrode sheet with a scraper. The active material loading of the obtained electrode sheet was 2-3 mg cm -2 When assembling the CR2025 button half-cell, the entire process is carried out in a high-purity argon-protected glove box, where the water and oxygen contents are controlled below 0.1 ppm. The assembly order is positive electrode shell → positive electrode → diaphragm → electrolyte → negative electrode → negative electrode shell. The positive electrode is a prepared circular electrode sheet, the negative electrode is a metal lithium sheet, the diaphragm is Celgrad 2500, and the electrolyte is 1.0 mol L -1The organic solution of LiPF6, the electrolyte solvent is a mixture of ethyl carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) in a volume ratio of 1:1:1. After the button battery is sealed with a sealing machine, it is left to stand for 6 hours before testing. The constant current charge and discharge test is carried out on the Xinwei battery tester. The test temperature is 25℃ and the voltage range of the charge and discharge test is 2.5~3.9V. The cycle performance curve under 0.5C conditions is as follows Figure 4 As shown, from Figure 4 It can be seen that the Li2Ru prepared in Example 1 0.925 Ti 0.0375 Cr 0.0375 The capacity retention rate of O3 is higher than that of Li2RuO3 in comparative example 1, and the capacity retention rate reaches 98.7% after 300 cycles at 0.5C. The capacity retention rate of Li2RuO3 prepared in comparative example 1 is only 67.9% after 300 cycles at 0.5C.

[0025] Example 2: The preparation method of the long-cycle lithium-rich ruthenium-based cathode material based on high-energy ball milling to control the morphology of this embodiment is carried out according to the following steps:

[0026] 1. Weigh 0.005267 mol (0.3892 g) of Li2CO3, 0.004309 mol (0.5735 g) of RuO2, 0.0002394 mol (0.01912 g) of TiO2, and 0.0001197 mol (0.01819 g) of Cr2O3 powder, mix them, and add them into a high-energy ball mill with agate balls and a ball-to-material mass ratio of 20:1. Mill at a speed of 300 rpm for 3 hours to obtain a mixed powder;

[0027] Second, the mixed powder was placed in a high-temperature furnace and calcined at 1000 ° C in air for 15 hours to obtain a long-cycle lithium-rich ruthenium-based cathode material with morphology controlled by high-energy ball milling. Its expression is Li2Ru 0.900 Ti 0.050 Cr 0.050 O3.

[0028] The same method as in Example 1 was used to prepare Li2Ru 0.900 Ti 0.050 Cr 0.050 The electrical properties of O3 were tested, and the results showed that the capacity retention rate reached 98.4% after 300 cycles at 0.5C.

[0029] Example 3: The preparation method of the long-cycle lithium-rich ruthenium-based cathode material based on high-energy ball milling to control the morphology of this embodiment is carried out according to the following steps:

[0030] 1. Weigh 0.005338 mol (0.3944 g) of Li2CO3 powder, 0.004124 mol (0.5489 g) of RuO2 powder, 0.0003638 mol (0.02906 g) of TiO2 powder, and 0.0001819 mol (0.02765 g) of Cr2O3 powder, mix them, and add them to a high-energy ball mill. The ball milling beads are made of agate balls, and the ball-to-material mass ratio is 20:1. Ball milling is carried out at a speed of 300 rpm for 3 hours to obtain a mixed powder;

[0031] Second, the mixed powder was placed in a high-temperature furnace and calcined at 1000 ° C in air for 15 hours to obtain a long-cycle lithium-rich ruthenium-based cathode material with morphology controlled by high-energy ball milling. Its expression is Li2Ru 0.850 Ti 0.075 Cr 0.075 O3.

[0032] The same method as in Example 1 was used to prepare Li2Ru 0.850 Ti 0.075 Cr 0.075 The electrical properties of O3 were tested, and the results showed that the capacity retention rate reached 97.2% after 300 cycles at 0.5C.

[0033] Example 4: The preparation method of the long-cycle lithium-rich ruthenium-based cathode material based on high-energy ball milling to control the morphology of this embodiment is carried out according to the following steps:

[0034] 1. Weigh 0.005484 mol (0.4052 g) of Li2CO3 powder, 0.003739 mol (0.4977 g) of RuO2 powder, 0.0005928 mol (0.04735 g) of TiO2 powder, and 0.0003275 mol (0.04977 g) of Cr2O3 powder, mix them, and add them into a high-energy ball mill. The ball milling beads are made of agate balls, and the ball-to-material mass ratio is 20:1. Ball milling is carried out at a speed of 300 rpm for 3 hours to obtain a mixed powder.

[0035] Second, the mixed powder was placed in a high-temperature furnace and calcined at 1000 ° C in air for 15 hours to obtain a long-cycle lithium-rich ruthenium-based cathode material with morphology controlled by high-energy ball milling. Its expression is Li2Ru 0.750 Ti 0.125 Cr 0.125 O3.

[0036] The same method as in Example 1 was used to treat the Li2Ru prepared in Example 4. 0.750 Ti 0.125 Cr 0.125The electrical properties of O3 were tested, and the results showed that the capacity retention rate reached 95.8% after 300 cycles at 0.5C.

[0037] Comparative Example 2: This embodiment differs from Example 1 in that the ball milling in step 1 has a ball milling speed of 200 rpm and a ball milling time of 2 hours. The other steps and parameters are the same as those in Example 1.

[0038] Comparative Example 3: This embodiment differs from Example 1 in that the ball milling in step 1 has a ball milling speed of 400 rpm and a ball milling time of 4 hours. The other steps and parameters are the same as those in Example 1.

[0039] The Li2Ru prepared in Comparative Example 2 and Comparative Example 3 were prepared in the same manner as in Example 1. 0.925 Ti 0.0375 Cr 0.0375 The electrical properties of O3 were tested, and the results showed that the Li2Ru prepared in Comparative Example 2 had a good electrical conductivity and good cycling performance at 0.5C for 300 cycles. 0.925 Ti 0.0375 Cr 0.0375 The O3 capacity retention rate is only 75.1%. 0.925 Ti 0.0375 Cr 0.0375 The O3 capacity retention rate is only 81.6%, which is lower than the capacity retention rate of the material prepared under the conditions of Example 1, indicating that too low or too high ball milling speed is not conducive to improving the material performance.

[0040] The above examples can prove that chromium improves the discharge capacity of the material, and titanium 1-x-y Ti x Cr y O3 can form stronger Ti-O bonds, which helps stabilize the crystal structure of Li2RuO3, improve its electrochemical performance, and prevent significant changes in the crystal structure, further increasing its discharge capacity and capacity retention. The ball milling and calcination conditions selected by the present invention, along with the rational introduction of titanium and chromium, can produce samples with significantly improved long-cycle performance, increasing the sample's discharge capacity, capacity retention, and lithium-ion diffusion rate. The preparation method is simple to operate, low-cost, and suitable for mass production.

Claims

1. A method for preparing a long-cycle lithium-rich ruthenium-based cathode material based on high-energy ball milling to control morphology, characterized in that: The method proceeds as follows:

1. According to the mass ratio of Li2CO3, RuO2, TiO2 and Cr2O3 powders of 1: (1.23-1.67): (0.04-0.14): (0.04-0.13), weigh Li2CO3, RuO2, TiO2 and Cr2O3 powders, mix them, add them into a high-energy ball mill, and ball mill them at a speed of 280-320 rpm for 2.8-3.2 hours to obtain a mixed powder; Second, the mixed powder is placed in a high-temperature furnace and calcined at 950-1050°C in an oxygen environment for 14-16 hours to obtain a long-cycle lithium-rich ruthenium-based cathode material with morphology controlled by high-energy ball milling; the chemical formula of this material is Li2Ru 1-x-y Ti x Cr y O3, where x=y=0.0375~0.

125.

2. The method for preparing a long-cycle lithium-rich ruthenium-based cathode material with morphology controlled by high-energy ball milling according to claim 1, characterized in that In step 1, the mass ratio of Li2CO3, RuO2, TiO2 and Cr2O3 powders is 1: (1.35~1.51): (0.04~0.14): (0.04~0.13).

3. The method for preparing a long-cycle lithium-rich ruthenium-based cathode material with morphology controlled by high-energy ball milling according to claim 1 or 2, characterized in that: The calcination temperature in step 2 is 1000° C. and the calcination time is 15 hours.

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