Preparation of Fe2O3 / MnO2 and SnO2 / MnO2 hetero-materials with Na-doped MnO2 as matrix and application thereof in negative electrode of lithium ion battery

Abstract

The application discloses a preparation method of a hetero-material taking sodium ion doped manganese dioxide as a base body as a negative electrode of a lithium ion battery. The application aims to provide better capacity performance, rate performance and cycle stability when applied as the negative electrode of the lithium ion battery. The application mainly comprises the following steps: 1, preparation of sodium ion doped manganese dioxide; 2, preparation of a composite material of triiron tetroxide and sodium ion doped manganese dioxide; and 3, preparation of a composite material of tin dioxide and sodium ion doped manganese dioxide. The prepared Fe2O3 / MnO2 hetero-structure lithium ion battery material has a specific capacity of 1441.7 and 730.7 mAh g ‑1 at a current density of 0.1 and 2 A g ‑1 , and a capacity retention rate of 95% after 900 cycle tests at a current density of 0.5 A g ‑1 .

Description

TECHNICAL FIELD

[0001] The present application relates to the field of material preparation and energy storage, in particular to a Fe2O3 / MnO2 and SnO2 / MnO2 heterostructure material with Na-doped MnO2 as a matrix and a study on the electrochemical lithium storage performance thereof. BACKGROUND

[0002] Metal oxides are of great potential as electrochemical energy storage materials, which are widely used in supercapacitors and lithium ion batteries, and also play an important role in solar cells and fuel cells. Due to the multi-electron transfer characteristics (2-8 electrons) of electrochemically active elements in the reaction process, metal oxides have a relatively high specific capacity, often exceeding 100 mAh g -1 However, most metal oxides have poor electrical conductivity and large volume changes during charging and discharging, which leads to poor cycle stability and electrochemical reversibility of metal oxide electrode materials, thus limiting their practical application. Building two-dimensional nanostructured materials is one of the effective strategies to solve the above problems, which can increase the contact area between the electrode and the electrolyte and improve the effective specific surface area of the electrode material.

[0003] Based on the above factors, considering the important role of nanostructure and structural defects in the field of electrochemical energy storage, defect engineering of nanostructured materials is an effective strategy to improve the energy storage properties of electrode materials. Fe2O3 / MnO2 and SnO2 / MnO2 heterostructure materials with abundant defect structures were prepared by mild cation substitution at room temperature using Na-doped manganese dioxide as raw material and were applied to lithium ion battery anodes. Fe2O3 / MnO2 and SnO2 / MnO2 heterostructure materials have a stacked layered structure of ultra-small nanosheets, and the material has abundant pore structures inside. The existence of a large number of atomic displacements at the grain contact interface of the heterostructure material leads to a large number of defects between the lattices, which have higher surface free energy and can provide electrochemical energy storage active sites, which is beneficial to the migration of electrolyte ions between the layers. At the same time, this preparation method using cation substitution reaction does not require a template, has the advantages of mild reaction conditions, high material yield, and simple preparation method. When used as a lithium ion battery anode, it can provide better capacity performance, rate performance and cycle stability.

[0004] In summary, the present application prepared a Fe2O3 / MnO2 and SnO2 / MnO2 heterostructure material with Na-doped MnO2 as a matrix, which obtained excellent electrochemical performance and has good application prospects as a lithium ion battery anode material. SUMMARY

[0005] The present application aims to design a nano-heterostructure composed of different metal oxides to improve the electrochemical performance of electrode materials, and to provide a Fe2O3 / MnO2 hetero-material with Na-doped MnO2 as a substrate.

[0006] The preparation method of the Fe2O3 / MnO2 and SnO2 / MnO2 hetero-materials with Na-doped MnO2 as a substrate for the negative electrode of a lithium ion battery is carried out according to the following steps:

[0007] I. Synthesis of sodium-doped manganese dioxide MnO2 at room temperature

[0008] A certain amount of NaCl is weighed and dissolved in 100 mL of deionized water. After stirring vigorously for 30 min, 0.5 g of KMnO4 is added to the above solution, and stirring is continued for 3 h. Then 75 mL of ethanol is measured and slowly added dropwise to the solution using a separatory funnel. Stirring is continued for 30 min, and after the reaction is completed, centrifugal washing is immediately performed until there is no Cl - - in the system, which is tested by using silver nitrate. After ultrasonic treatment, freeze-drying is performed to obtain a sample, which is denoted as MnO2-Na-70. The addition amount of NaCl is 70 g. The MnO2-Na-70 sample is prepared into a dispersion solution for standby;

[0009] II. Synthesis of iron sesquioxide / manganese dioxide Fe2O3 / MnO2 in a water bath

[0010] The prepared MnO2-Na-70 is directly used after centrifugal washing and ultrasonic treatment as a MnO2 precursor. 100 mL of the MnO2 dispersion solution is taken, in which the molar mass of MnO2 in the MnO2 dispersion solution is 1.5 mmol. Ultrasonic treatment is performed until the dispersion is uniform. 3 mmol of ferrous perchlorate is weighed and dissolved in 50 mL of distilled water. The MnO2 suspension and the ferrous perchlorate solution are mixed, and stirring is performed vigorously in a 60℃ water bath for 12 h. Subsequently, centrifugal washing is performed, and the sample is dried at 80℃ for 24 h to obtain a red-brown powder, which is denoted as FM-2-12. As a comparison, the water bath time is extended to 24 h, and the other conditions remain unchanged. The dried sample is denoted as FM-2-24. 1.5 mmol of ferrous perchlorate is weighed and dissolved, and the other conditions remain unchanged. The prepared sample is denoted as FM-1-12.

[0011] III. Synthesis of tin dioxide / manganese dioxide SnO2 / MnO2 in a water bath

[0012] ​The prepared MnO2-Na-70 is directly ultrasonic after centrifugal washing, as MnO2 precursor, 75 mL MnO2 dispersion liquid is taken, wherein the molar mass of MnO2 in the MnO2 dispersion liquid is 1.5 mmol, ultrasonic until uniformly dispersed, 1.5 mmol stannous sulfate is weighed and dissolved in 30 mL 0.48 mol / L H2SO4 solution -1 The manganese dioxide suspension and stannous sulfate solution are mixed, stirred at room temperature for 12 h, and dried at 80 DEG C after centrifugal washing to obtain a light yellow powder, which is recorded as SM-1-24.

[0013] Compared with the prior art, the present application has the following beneficial effects:

[0014] (1) The present application prepares Fe2O3 / MnO2 and SnO2 / MnO2 heterostructures with defects by cation replacement method, the material has relatively abundant defect structure and heterostructure interface, and the specific surface area is improved to a certain extent compared with MnO2-Na. The introduction of abundant defect structure and pore structure in the material increases the redox active site and ion transmission channel, which is beneficial to improve the charge transfer rate in the charging and discharging process and the effective contact area of active material.

[0015] (2) Na + Ion doping and defect structure can also effectively improve the conductivity of the material, and the defect structure has higher surface free energy, which can provide more electrochemical energy storage sites for the electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a micro-morphology photo of a Fe2O3 / MnO2 hetero-material doped with Na-doped MnO2 prepared by the present application;

[0017] Figure 2 is a crystal structure and chemical composition of a Fe2O3 / MnO2 hetero-material doped with Na-doped MnO2 prepared by the present application;

[0018] Figure 3 is a micro-morphology photo of a SnO2 / MnO2 hetero-material doped with Na-doped MnO2 prepared by the present application;

[0019] Figure 4 is a crystal structure and chemical composition of a SnO2 / MnO2 hetero-material doped with Na-doped MnO2 prepared by the present application;

[0020] Figure 5 is the electrochemical performance of a Fe2O3 / MnO2 and SnO2 / MnO2 hetero-material doped with Na-doped MnO2 prepared by the present application;

[0021] Figure 6is a kind of Fe2O3 / MnO2 and SnO2 / MnO2 heterostructure material with Na-doped MnO2 prepared by the preparation of impedance and rate performance;

[0022] Figure 7 is the micro-morphology photo of Fe2O3 / MnO2 heterostructure material with Na-doped MnO2 prepared by the preparation. DETAILED DESCRIPTION

[0023] Specific embodiment one: a preparation method of Fe2O3 / MnO2 and SnO2 / MnO2 heterostructure material with Na-doped MnO2, specifically is carried out according to the following steps:

[0024] I. Synthesis of sodium-doped manganese dioxide MnO2 at room temperature

[0025] A certain amount of NaCl is weighed, dissolved in 100 mL of deionized water, and after stirring vigorously for 30 min, 0.5 g of KMnO4 is added to the above solution, and stirred vigorously for 3 h. Then 75 mL of ethanol is measured and slowly added dropwise to the solution using a separatory funnel, and stirring is continued for 30 min. After the reaction is completed, centrifugal washing is immediately carried out until there is no Cl - , wherein Cl - is tested by silver nitrate, and after ultrasonic treatment, freeze-drying is carried out to obtain a sample, which is denoted as MnO2-Na-70. The addition amount of NaCl is 70 g. The MnO2-Na-70 sample is prepared into a dispersion liquid for standby;

[0026] II. Synthesis of iron trioxide / manganese dioxide Fe2O3 / MnO2 in water bath

[0027] The prepared MnO2-Na-70 is directly ultrasonically treated after centrifugal washing for standby, as a MnO2 precursor. 100 mL of MnO2 dispersion liquid is taken, wherein the molar mass of MnO2 in the MnO2 dispersion liquid is 1.5 mmol. Ultrasonic treatment is carried out until the dispersion is uniform. 3 mmol of ferrous perchlorate is weighed and dissolved in 50 mL of distilled water. The MnO2 suspension and the ferrous perchlorate solution are mixed, and then stirred vigorously in a 60℃ water bath for 12 h. Subsequently, centrifugal washing is carried out, and then the sample is dried at 80℃ for 24 h to obtain a red-brown powder, which is denoted as FM-2-12. As a comparison, the water bath time is extended to 24 h, and the other conditions remain unchanged. The dried sample is denoted as FM-2-24. 1.5 mmol of ferrous perchlorate is weighed and dissolved, and the other conditions remain unchanged. The prepared sample is denoted as FM-1-12.

[0028] III. Synthesis of tin dioxide / manganese dioxide SnO2 / MnO2 in water bath

[0029] The prepared MnO2-Na-70 is directly used after centrifugal washing and ultrasonic treatment as MnO2 precursor. 75 mL of MnO2 dispersion liquid is taken, wherein the molar mass of MnO2 in the MnO2 dispersion liquid is 1.5 mmol, and the mixture is ultrasonically treated until uniformly dispersed. 1.5 mmol of stannous sulfate is weighed and dissolved in 30 mL of 0.48 mol / L H2SO4 solution. -1 The manganese dioxide suspension and the stannous sulfate solution are mixed, stirred at room temperature for 12 h, washed by centrifugation, and dried at 80°C to obtain a light yellow powder, which is denoted as SM-1-24.

[0030] Specific embodiment two: a preparation method of Fe2O3 / MnO2 and SnO2 / MnO2 heterostructures doped with Na-doped MnO2, which is specifically performed according to the following steps:

[0031] The difference between this embodiment and the specific embodiment one is that the amount of sodium chloride added in the preparation of MnO2-Na in step one is 70 g. The other steps are the same as those in the specific embodiment one.

[0032] Specific embodiment three: a preparation method of Fe2O3 / MnO2 and SnO2 / MnO2 heterostructures doped with Na-doped MnO2, which is specifically performed according to the following steps:

[0033] The difference between this embodiment and the specific embodiments one and two is that the water bath time in step two is extended to 24 h to obtain FM-2-24. The other steps are the same as those in the specific embodiments one and two.

[0034] Specific embodiment four: a preparation method of Fe2O3 / MnO2 and SnO2 / MnO2 heterostructures doped with Na-doped MnO2, which is specifically performed according to the following steps:

[0035] The difference between this embodiment and the specific embodiments one, two and three is that the amount of ferrous perchlorate added is 1.5 mmol. The other steps are the same as those in the specific embodiments one, two and three.

[0036] The effect of the present application is verified by the following test:

[0037] The specific embodiment of the present application is a preparation method of Fe2O3 / MnO2 and SnO2 / MnO2 heterostructures doped with Na-doped MnO2, which is specifically performed according to the following steps:

[0038] I. Room temperature synthesis of sodium-doped manganese dioxide MnO2

[0039] A certain amount of NaCl was weighed, dissolved in 100 mL of deionized water, stirred vigorously for 30 min, then 0.5 g of KMnO4 was added to the above solution, stirred vigorously for 3 h, then 75 mL of ethanol was measured and slowly added to the solution with a separatory funnel, and stirring was continued for 30 min. After the reaction was completed, centrifugal washing was immediately performed until there was no Cl - , wherein Cl - was tested by silver nitrate, and after ultrasonic treatment, freeze-drying was performed to obtain a sample, which was recorded as MnO2-Na-70, wherein the amount of added NaCl was 70 g. The MnO2-Na-70 sample was prepared into a dispersion solution for standby;

[0040] II. Water bath synthesis of Fe2O3 / MnO2

[0041] The prepared MnO2-Na-70 was directly ultrasonically treated after centrifugal washing for standby as a MnO2 precursor. 100 mL of MnO2 dispersion solution was taken, wherein the molar mass of MnO2 in the MnO2 dispersion solution was 1.5 mmol, and ultrasonic treatment was performed until dispersion was uniform. 3 mmol of ferrous perchlorate was weighed and dissolved in 50 mL of distilled water. After mixing the MnO2 suspension and the ferrous perchlorate solution, vigorous stirring was performed in a water bath at 60°C for 12 h. Subsequently, centrifugal washing was performed, and the sample was dried at 80°C for 24 h to obtain a red-brown powder, which was recorded as FM-2-12. As a comparison, the water bath time was extended to 24 h, and the other conditions were unchanged. The dried sample was recorded as FM-2-24. 1.5 mmol of ferrous perchlorate was weighed and dissolved, and the other conditions were unchanged. The prepared sample was recorded as FM-1-12.

[0042] III. Water bath synthesis of SnO2 / MnO2

[0043] The prepared MnO2-Na-70 was directly ultrasonically treated after centrifugal washing for standby as a MnO2 precursor. 75 mL of MnO2 dispersion solution was taken, wherein the molar mass of MnO2 in the MnO2 dispersion solution was 1.5 mmol, and ultrasonic treatment was performed until dispersion was uniform. 1.5 mmol of stannous sulfate was weighed and dissolved in 30 mL of 0.48 mol L -1 of sulfuric acid solution. The MnO2 suspension and the stannous sulfate solution were mixed, and stirring was performed at room temperature for 12 h. After centrifugal washing, a light yellow powder was obtained by drying at 80°C, which was recorded as SM-1-24.

[0044] The electrode slurry of the lithium ion battery is prepared first in the electrochemical test. The active material, carbon black and binder are uniformly mixed in a mass ratio of 8:1:1 and then ground. The ground mixture is then transferred to a weighing bottle, an appropriate amount of 1-methyl-2-pyrrolidone (NMP) is added, and continuous stirring is performed for 30 min until a thick state is obtained for standby use. The copper foil is cut to the appropriate size, washed, wiped dry with alcohol, and then the slurry is uniformly applied to the clean copper foil using a spatula. The copper foil is dried in a vacuum oven at 120°C for 12 h, then sliced to obtain a round piece with a diameter of 12 mm, and then placed in a bag for standby use. The slicing is performed using a button cell punching machine (MSK-T-06). The assembly of the lithium ion battery is performed in a glove box (MB 10) with argon as the protective gas. The components required for the button cell are placed in the battery shell in the order of the electrode sheet, the gasket, the spring sheet, and the electrolyte (LB-001), and then the button cell is packaged using a button cell packaging machine (MT-160D). The lithium ion battery obtained by assembly needs to be left to stand for 24 h before the electrochemical test. Polyethylene separator The electrode sheet, the gasket and the spring sheet are sequentially placed in the battery shell, which is a CR2032 stainless steel battery shell, and the electrolyte (LB-001) is added, and finally the button cell packaging machine (MT-160D) is used for packaging operation. The lithium ion battery obtained by assembly needs to be left to stand for 24 h before the electrochemical test.

[0045] Figure 1 is a transmission electron microscope image of Fe2O3 / MnO2. It can be seen that the sample has a block structure formed by a large number of nanosheets stacked together. Measurement shows that the diameter of the nanosheets is mostly concentrated at about 3 nm, the size is uniform, and the grain boundary is clearly visible. Figure 1 c and d are high-resolution transmission electron microscope images of Fe2O3 / MnO2. Figure 1 The circled part in c can clearly observe the microstructure of the nanosheets connected into sheets. The boundary of the material can see that the sheet layer structure formed by the connection of the nanosheets is stacked layer by layer, and the clear lattice fringes can be observed. Through the measurement and calculation of the lattice fringes, it can be known that the lattice spacings of 0.25 and 0.37 nm in the sample correspond to the (012) and (110) crystal faces of hematite type ferric oxide, and the crystal face spacing of 0.44 nm corresponds to the (111) crystal face of manganese dioxide. It is proved that there are both ferric oxide and manganese dioxide in the Fe2O3 / MnO2 material.

[0046] Figure 2 is the XPS total spectrum of the Fe2O3 / MnO2 hetero material, and the characteristic peaks of Fe2p, Mn2p, O1 s and C1s in the spectrum are obvious. The spectrum of several characteristic peaks is then processed by fitting and peak separation. Figure 2 As shown in b, in the high-resolution Fe2p spectrum, there are two obvious characteristic peaks at binding energies of 725.3 and 711.6 eV, which correspond to Fe2p 3 / 2 and Fe2p 1 / 2In addition, two satellite peaks can be observed at 734.1 and 719.1 eV, which are consistent with the XPS spectrum of Fe2O3 reported in the literature. Figure 2 c is the high resolution Mn 2p spectrum, which can be fitted by two peaks at 653.8 and 642.3 eV, corresponding to Mn 4+ 1 / 2 3 / 2 , which is the same as the result of XRD test. The Mn 2p 1 / 2 can be fitted by two Gaussian functions at 655.3 and 653.7 eV, corresponding to Mn(IV) and Mn(III), respectively. The Mn 2p 3 / 2 can be fitted by two peaks at 643.4 and 642.1 eV, corresponding to Mn(IV) and Mn(III), respectively. The content of Mn(III) in the sample can be calculated by the area ratio of the fitting curve, and the content of Mn(III) in the sample is 29.8%. Figure 5 .9d is the high resolution O 1s spectrum, which can be fitted by three Gaussian functions, i.e. the physical adsorption oxygen (Oads) at 532.1 eV, the hydroxyl oxygen (Ohyd) at 531.4 eV and the lattice oxygen (Olatt) at 529.9 eV.

[0047] Figure 3 is the transmission electron microscope image of SM-1-24, in which the SM-1-24 sample is a large block structure formed by the stacking of uniform small nanosheets, and there are some pores. This structure is consistent with the microstructure of FM-2-12 sample, and is the same as the microstructure of MnO2-Na-70 sample, indicating that the microstructure can be transferred in the synthesis method of cation exchange. In Figure 3 c is the high resolution transmission electron microscope of SM-1-24 material, and the lattice spacing of SM-1-24 sample is 0.33 nm, which corresponds to the (110) crystal plane of SnO2. The grain size of nanosheet is concentrated at about 2 nm, which is connected to each other, has clear lattice fringes, and the boundary of nanosheet is clear. After careful observation, it can be seen that there are defect structures in the red circle part, and there are a certain amount of similar defect structures, which may be due to the existence of Mn and Na atoms in the reaction process, causing the atoms to deviate from the original position, causing lattice distortion. Under normal circumstances, the surface free energy of these positions is higher, and has higher energy storage activity than other positions, which is conducive to the better performance of the material. Figure 3 ​​d is the selected area electron diffraction pattern of SM-1-24 material. The diffraction rings are clearly visible in the figure, indicating the good crystallinity of the material. After calculation, it was determined that the three diffraction rings correspond to the (110), (101) and (211) crystal planes of tin dioxide material, respectively.

[0048] Figure 4 The image shows the total XPS spectrum of the SnO2 / MnO2 sample, in which four elements, Sn, Mn, O, and C, can be observed. Figure 4 b is the high-resolution spectrum of Sn3d, and the characteristic peak at 496.25 eV corresponds to Sn3d. 3 / 2 The obvious characteristic peak at 487.7 eV corresponds to Sn 3d 5 / 2 This is consistent with the XPS spectrum of SnO2 reported in the literature. Figure 1 To. Figure 5 .10c is the XPS spectrum of the Mn 2p region. 1 / 2 and Mn 2p 3 / 2 The characteristic peaks are located at 654.3 and 642.3 eV, respectively. Gaussian fitting was then performed, and both characteristic peaks could be obtained by fitting two Gaussian functions corresponding to Mn(III) and Mn(IV). The fitted peaks for Mn(III) are located at 651.15 and 642.1 eV, respectively, while the fitted peaks for Mn(IV) are located at 654.4 and 643.4 eV. Calculation of the fitted peak areas for Mn(II) and Mn(IV) yielded a Mn(III) content of 35.8%. Figure 4 d represents the XPS spectrum of the O1s region of the sample, which can be obtained by fitting three Gaussian functions at 533.4, 532.3, and 531.3 eV, respectively, corresponding to physically adsorbed oxygen (Oads), hydroxyl oxygen (Ohyd), and intercalary oxygen (Olatt).

[0049] Figure 5 The figures show the constant current charge-discharge curves for the first three cycles of the FM-2-12, SM-1-24, and MnO2-Na-70 electrodes, with a measured current density of 0.1 Ag. -1 . Figure 5 The first-cycle discharge specific capacity of the FM-2-12 electrode in a is 2004.7 mAh g. -1 The first charge capacity is 1450.6mAh g. -1 The calculated coulombic efficiency was 72.6%. These capacity losses are due to the decomposition of the organic electrolyte and the formation of a solid electrolyte interfacial film during the first charge-discharge cycle. The charge-discharge plateaus are consistent with the CV curves, located near 0.8 and 1.6 V, respectively. The plateaus did not change position during the charge-discharge process, indicating the good electrochemical stability of the FM-2-12 electrode material. Figure 5b is the galvanostatic charge-discharge curves of SM-1-24 electrode at 0.1 Ag -1 The first round of charge-discharge specific capacity is 1076.7 and 2028.4 mAh g -1 , and the coulombic efficiency is 53.1%. The second and third round of charge-discharge curves are basically coincident, and the platform does not produce offset, which reflects the stable voltage output of SM-1-24 electrode. As Figure 5 c is the first three rounds of galvanostatic charge-discharge curves of MnO2-Na-70 electrode material, and the test current density is the same as that of other samples. The first round of charge-discharge specific capacity is 1076.8 and 1985 mAh g -1 , and the coulombic efficiency is 54.2%. Two voltage platforms can be observed during the charging process, which are located near 1.2 V and 2.1 V, respectively, which is due to the multi-valence characteristics of the metal Mn during the oxidation process. This feature can provide additional capacity during the electrochemical cycle test, showing excellent capacity performance. In order to further determine the capacity performance of FM-2-12, SM-1-24 and MnO2-Na-70 electrode materials, the specific capacity of the three electrode materials was calculated and compared under the test of 0.1, 0.2, 0.5, 1 and 2 Ag -1 current density, and the rate performance curve comparison diagram is shown in Figure 5 d. In the figure, the rate performance of FM-2-12 electrode is outstanding, and the specific capacity calculated under 0.1, 0.2, 0.5, 1 and 2 Ag -1 current density is 1441.7, 1308.2, 1090.1, 929 and 730.7 mAh g -1 , respectively. Then the current density gradually decreases to 0.1 Ag -1 , and the specific capacity increases to 1537.1 mAh g -1 . This may be due to the opening of lithium ion transmission channel, which improves the electrolyte wettability of the electrode. At the same time, there are a large number of defect structures in FM-2-12 electrode material, and the surface free energy of this structure is high, and the electrochemical activity is strong, which can provide higher specific capacity for the electrode. The specific capacity of SM-1-24 electrode under different current densities (0.1, 0.2, 0.5, 1 and 2 Ag -1 ) is 1093.7, 979.5, 836.3, 718.5 and 621.6 mAh g -1 , respectively, and the specific capacity is 829.7 mAh g -1 when the current density is reduced to 0.1 Ag -1. After the rate performance test, the specific capacity of SM-1-24 electrode material is slightly lost, which may be due to the intrinsic properties of tin dioxide material, tin dioxide material has poor conductivity, and the volume change in the process of cyclic charge and discharge can reach 300%. After the charge and discharge reaction of large current, the lithium ion insertion and extraction leads to the fracture of tin dioxide electrode and the shedding of active material, resulting in capacity loss. The specific capacity of MnO2-Na-70 electrode under the same current density is 1124.1, 978.1, 738.2, 531.5 and 311 mAh g -1 When the current density returns to 0.1 Ag -1 , the specific capacity is 994.7 mAh g -1 , indicating good reversibility.

[0050] In order to further explore the electrochemical performance of FM-2-12 electrode, it was tested for cycle stability under the current density of 1 and 2 Ag -1 . As shown in Fig. Figure 6 a, under the current density of 1 Ag -1 , the specific capacity of FM-2-12 electrode in the cycle stability curve of the first 100 cycles can be observed to decrease rapidly and then slowly rise, which is due to the process of lithium ion transmission channel construction under large current density. In the subsequent 100-700 cycles, the specific capacity gradually stabilizes and gradually increases, and the specific capacity retention rate is 108%. However, the cycle stability curves of MnO2-Na-70 and SM-1-24 electrodes show a gradually decaying trend, and the specific capacity retention rates are 56% and 23%, respectively. Both of these two electrodes have a large volume expansion during the cycle process, and the rapid deintercalation of lithium ions under large current density leads to the gradual collapse of the electrode structure, resulting in large capacity loss. Figure 6 b is the cycle stability curve of FM-2-12 under the current density of 2 Ag -1 , it can be observed in the figure that the specific capacity gradually decays in the first 100 cycles, and enters a stable stage after 100 cycles. The initial capacity decay is partly due to the decomposition of the initial electrolyte and the formation of the solid electrolyte interface film, and the other part is because the ions are rapidly transported in the electrode material under the large current density of 2 Ag -1 , which causes the structure of the electrode material to change. In the subsequent 100-700 cycles, the specific capacity of the electrode gradually stabilizes, only because the internal structure of the material gradually stabilizes, and the specific capacity retention rate is 90%.

Claims

1. A method for preparing Fe2O3 / MnO2 and SnO2 / MnO2 heterostructures with abundant defect structures by mild cation substitution method at room temperature using Na-doped manganese dioxide as raw material, and applying it to the preparation of lithium ion battery negative electrode, which is carried out according to the following steps: I. Synthesis of sodium-doped manganese dioxide MnO2 at room temperature A certain amount of NaCl was weighed, dissolved in 100 mL of deionized water, and after 30 minutes of vigorous stirring, 0.5 g of KMnO4 was added to the above solution, and stirred vigorously for 3 hours. Then 75 mL of ethanol was measured and slowly added dropwise to the solution using a separatory funnel, and stirring was continued for 30 minutes. After the reaction was completed, centrifugal washing was immediately performed until there was no Cl - in the system - was detected using silver nitrate. After ultrasonic treatment and freeze-drying, the obtained sample was recorded as MnO2-Na-70, wherein the amount of added NaCl was 70 g. The MnO2-Na-70 sample was prepared into a dispersion solution for standby use. II. Synthesis of Fe2O3 / MnO2 by water bath The prepared MnO2-Na-70 is directly used after centrifugal washing and ultrasonic treatment as MnO2 precursor, 100 mL MnO2 dispersion liquid is taken, the molar mass of MnO2 in the MnO2 dispersion liquid is 1.5 mmol, and ultrasonic treatment is performed until the dispersion is uniform, 3 mmol of ferrous perchlorate is weighed and dissolved in 50 mL of distilled water, the MnO2 suspension liquid and the ferrous perchlorate solution are mixed, and then stirred vigorously in a 60℃ water bath for 12 h, followed by centrifugal washing, and then dried at 80℃ for 24 h to obtain a red-brown powder, which is recorded as FM-2-12; as a comparison, the water bath time is extended to 24 h, and the other conditions remain unchanged, and the dried sample is recorded as FM-2-24; 1.5 mmol of ferrous perchlorate is weighed and dissolved, and the other conditions remain unchanged, and the prepared sample is recorded as FM-1-12; III. Synthesis of SnO2 / MnO2 by water bath The prepared MnO2-Na-70 was directly used after centrifugal washing and ultrasonic treatment as MnO2 precursor. 75 mL of MnO2 dispersion liquid was taken, in which the molar mass of MnO2 in the MnO2 dispersion liquid was 1.5 mmol, and the mixture was ultrasonically treated until it was uniformly dispersed. 1.5 mmol of stannous sulfate was weighed and dissolved in 30 mL of 0.48 mol / L H2SO4 solution, and then the mixture was stirred at room temperature for 12 h. After centrifugal washing, the mixture was dried at 80°C to obtain a light yellow powder, which was recorded as SM-1-24. -1 The manganese dioxide suspension and the stannous sulfate solution were mixed, and the mixture was stirred at room temperature for 12 h. After centrifugal washing, the mixture was dried at 80°C to obtain a light yellow powder, which was recorded as SM-1-24.

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