WO2019095180A1 - Lithium-iron-oxygen composite material, preparation method therefor and lithium-ion battery - Google Patents

Abstract

Disclosed are a lithium-iron-oxygen composite material and a preparation method therefor, the composite material comprising lithium iron oxide and a carbon layer covering the surface of the lithium iron oxide, wherein the lithium iron oxide is LixFeyO 3. Also disclosed is a lithium-ion battery, wherein the material of a negative electrode thereof is the lithium-iron-oxygen composite material. As the material of the negative electrode of the lithium-ion battery, the lithium-iron-oxygen composite material has a higher initial coulombic efficiency and an excellent cyclic stability.

Description

Lithium iron oxide composite material, preparation method thereof and lithium ion battery Technical field

The invention relates to the technical field of battery materials, in particular to a lithium iron oxygen composite material, a preparation method thereof and a lithium ion battery.

Background technique

Lithium-ion battery (LIB) is one of the most successful rechargeable lithium batteries with high energy density and long cycle life. The first generation LIB consisting of a LiCoO ₂ positive electrode and a graphite negative electrode provides a high specific energy of about 180 Wh·kg ^-1 , which is about 5 times that of a lead-acid battery. Since then, other positive electrode materials have been successfully developed, such as olivine-type LiFePO ₄ , spinel-type LiMn ₂ O ₄ and layered LiNi _x Co _y Mn _z O ₂ , and further improve battery performance and reduce cost.

The choice of commercial anode materials is primarily limited to graphite materials. Although a large number of other negative electrode materials having higher capacity have been developed, such as alloy-type elements (such as Si, Sn, etc.) and converted transition metal oxides (such as iron oxide, cobalt oxide, etc.), such materials are difficult to fully satisfy. Requirements for scaled applications.

The most critical disadvantages of the above negative electrode materials are reflected in the following three aspects: poor cycle stability, slow reaction kinetics, and low coulombic efficiency (CE). The main causes of the first two problems are the dramatic volume change of the material during lithium insertion and the poor lithium ion/electron transport; the problem of low coulombic efficiency, especially in the initial stage, is mostly ignored by the researchers, during the initial charging process, The decomposition of the electrolyte and the lithiation reaction of the negative electrode often form a solid electrolyte interface (SEI) on the surface of the negative electrode, forming SEI and irreversible Li loss in the negative electrode, resulting in low CE and high specific capacity loss.

When the carbonaceous support/coating is used as the negative electrode material, it exhibits good cycle stability and rate performance due to the buffering effect of the carbon layer, reduced lithium ion diffusion distance, and improved electron conductivity; however, its enlarged surface area And more significant side reactions, the use of carbon-containing nanocomposites, the Coulomb efficiency reduction will be further deteriorated. In view of this, it is urgent to provide a lithium ion battery anode material in order to solve the three problems of the above anode material.

Summary of the invention

The technical problem solved by the invention is to provide a lithium iron oxide composite material, and the lithium iron oxygen composite material provided by the invention has high initial coulombic efficiency and excellent cycle as a negative electrode material of a lithium ion battery. Ring stability.

In view of this, the present application provides a lithium iron oxide composite material comprising a lithium iron oxide as shown in formula (I) and a carbon layer coated on the surface of the lithium iron oxide;

Li _x Fe _y O ₃ (I);

Where x is greater than 0 and less than or equal to 1.2;

y is 1.5 to 2.

Preferably, the carbon layer has a thickness of 1.5 to 2.5 nm.

Preferably, the x is from 0.5 to 1.1, and the y is from 1.7 to 1.9.

Preferably, the lithium iron oxide composite has a size of 20 to 100 nm.

The application provides a preparation method of the lithium iron oxide composite material, which comprises the following steps:

The carbonyl-containing iron-based compound is reacted with a lithium source in a solvent to obtain a precursor solution;

The precursor solution is heated to obtain a lithium iron oxide composite material.

Preferably, the carbonyl group-containing iron-based compound is one or more selected from the group consisting of iron pentacarbonyl, hexacarbonyldiiron and tricarbonyl pentoxide; the lithium source is selected from the group consisting of lithium hydroxide and lithium hydrogencarbonate. One or more of lithium nitrate and lithium carbonate.

Preferably, the molar ratio of the iron-based compound to the lithium source is (10-20): (5-76).

Preferably, the heating is performed under a flow of N ₂ , the heating temperature is 300 to 1000 ° C, the heating time is 0 to 10 h, and the heating is performed at a heating rate of 10 to 20 ° C/min.

Preferably, the temperature of the precursor solution is 40 to 50 ° C before heating.

The present application also provides a lithium ion battery comprising a positive electrode and a negative electrode, the material of the negative electrode being the lithium iron oxide composite material described in the above scheme or the lithium iron oxide composite material prepared by the preparation method described in the above scheme.

The present application provides a lithium iron oxide composite material comprising a lithium iron oxide of the formula Li _x Fe _y O ₃ and a carbon layer coated on the surface of the lithium iron oxide; the above-mentioned lithium ferrite provided by the present application The composite material has pre-embedded Li, which largely compensates for the Li loss in the first charge and discharge cycle and improves the initial coulombic efficiency; and at the same time, the lithium is caused by the interaction of the cladding carbon layer and the lithium iron oxide Ferrite composites also have excellent cycle stability. The experimental results show that the lithium iron oxide composite anode of the present application has a high initial coulombic efficiency of up to 90%; a high specific volume of up to 1000 mAh·g ^-1 and a long life of more than 400 cycles.

DRAWINGS

1 is a set of physical property characterization of a lithium iron-oxygen composite material prepared in Example 1 of the present invention;

2 is a set of electrochemical performance of a lithium iron oxide composite negative electrode prepared in Example 1 of the present invention;

3 is a typical cyclic voltammogram of a lithium iron oxide composite material and a Fe ₂ O ₃ electrode prepared in Example 1 of the present invention;

4 is an XRD pattern, a first discharge specific capacity curve, and a first efficiency graph of a lithium iron oxide composite material synthesized by different ratios of LiOH and Fe(CO) ₅ at 500 ° C;

Figure 5 is an XRD pattern, a first capacity curve and a coulombic efficiency curve of a lithium iron oxide composite material synthesized at different temperatures;

6 is a graph showing a first charge and discharge curve, a rate performance curve, and a cycle stability curve of a lithium iron oxide composite material and a Fe ₃ O ₄ electrode prepared in Example 1 of the present invention;

7 is a set of electrochemical performance of a full-cell battery composed of a lithium iron-oxygen composite material prepared in Example 1 and Fe ₂ O ₃ respectively;

8 is a graph showing the first charge and discharge curves of the lithium iron oxide composite electrode half-cell prepared in Example 1.

Detailed ways

The present invention has been described in detail with reference to the preferred embodiments of the present invention.

In view of the problems of poor cycle stability, low initial coulombic efficiency and high preparation cost of lithium ion battery anode materials in the prior art, the present application provides a lithium iron oxide composite material, which describes a low cost lithium iron oxide composite material. , as a low-capacity anode material with low initial Li loss and stable cycle performance; at the same time, the chemical synthesis of the lithium-iron-oxygen composite is similar to the partially lithiated Fe ₂ O ₃ obtained in the electrochemical pathway, and Significantly improve the cycle stability of the material, its discharge reversible specific capacity is 1000mAh·g ^-1 ; the pre-intercalation of lithium in lithium-iron-oxygen composite compensates for the irreversible loss of lithium during the first cycle, providing high first efficiency of up to 90%, far Higher than the traditional lithium iron oxide anode. Specifically, the present application provides a lithium iron oxide composite material comprising a lithium iron oxide as shown in formula (I) and a carbon layer coated on the surface of the lithium iron oxide;

Li _x Fe _y O ₃ (I);

Where x is greater than 0 and less than or equal to 1.2;

y is 1.5 to 2.

In the lithium iron oxide composite material provided by the present application, the lithium iron oxide may be abbreviated as LFO, and thus the lithium iron oxide composite material is a carbon layer coated LFO composite material. The lithium iron oxide includes only Li, Fe and O elements, wherein x is greater than 0 and less than or equal to 1.2, and y is 1.5 to 2; in a specific embodiment, the x is 0.5 to 1.1, and the y is 1.7 to ～ 1.9; More specifically, the lithium iron oxide has a molecular formula of Li _1.03 Fe _1.87 O ₃ , Li _0.51 Fe _1.9 O ₃ , Li _0.62 Fe _1.9 O ₃ , Li _1.05 Fe _1.86 O ₃ , Li _1.1 Fe _1.9 O ₃ , Li _1.1 Fe _1.87 O ₃ , Li _1.03 Fe _1.82 O ₃ , Li _1.03 Fe _1.82 O ₃ , Li _0.5 Fe _1.9 O ₃ , Li _0.97 Fe _1.82 O ₃ , Li _0.8 Fe _1.82 O ₃ , Li _0.6 Fe _1.82 O ₃ , Li _0.92 Fe _1.7 O ₃ , Li _0.95 Fe _1.7 O ₃ or Li _{0. 53} Fe _1.9 O ₃ .

According to the present invention, the carbon layer in the lithium iron-oxygen composite material is coated on the surface of the LFO and has a thickness of 1.5 to 2.5 nm. In a specific embodiment, the thickness of the carbon layer is 1.55 to 2.40 nm. In the present application, the thickness of the carbon layer affects the performance of the lithium iron oxide. If the thickness of the carbon layer is too thin, the carbon content in the electrode material is decreased, and the overall conductivity of the material is lowered, thereby affecting the rate performance of the battery; Too thick, on the one hand, the increase of carbon content will increase the specific surface area of the material, resulting in an increase in the volume of the SEI film, thereby increasing the loss of the first irreversible lithium ion and reducing the first coulombic efficiency; on the other hand, increasing the carbon content will reduce the active material at the electrode. The specific gravity in the material causes the overall energy density of the electrode material to decrease.

The application also provides a preparation method of the lithium iron oxide composite material, comprising the following steps:

The carbonyl-containing iron-based compound is reacted with a lithium source in a solvent to obtain a precursor solution;

The precursor solution is heated to obtain a lithium iron oxide composite material.

In the process of synthesizing the lithium iron-oxygen composite material, the hydroxyl group-containing iron-based compound is specifically selected from one or more selected from the group consisting of iron pentacarbonyl, hexacarbonyldiiron and tridecacarbonyl triiron, and the lithium source is selected. One or more of lithium hydroxide, lithium hydrogencarbonate, lithium nitrate and lithium carbonate. The solvent is an organic solvent well known to those skilled in the art, and the present application is not particularly limited. In a specific embodiment, the solvent is selected from the group consisting of ethanol. During this process, a nucleophilic reaction of a carbonyl-containing iron-based compound with a lithium source is carried out with a continuous hydroxyl group to obtain a lithium iron-oxygen composite precursor solution. Taking the carbonyl-containing iron-based compound as pentacarbonyl iron and the lithium source as lithium hydroxide, the specific reaction formula of the two reactions is as follows:

LiOH+Fe(CO) ₅ →Li[Fe(CO) ₄ COOH]

Li[Fe(CO) ₄ COOH]+LiOH→Li[HFe(CO) ₄ ]+LiHCO ₃

LiHCO ₃ +LiOH→Li ₂ CO ₃ +H ₂ O

Li[HFe(CO) ₄ ]+LiOH→Li ₂ [Fe(CO) ₄ ]+H ₂ O.

The present application then heats the above lithium iron oxide composite precursor solution to obtain a lithium iron oxide composite material. The process is specifically: maintaining the precursor solution at 40 to 50 ° C, evaporating ethanol under a stream of N ₂ , and then heating to obtain a lithium iron oxide composite material. The heating temperature is 300 to 1000 ° C, the time is 0 to 10 h, and the heating rate is 10 to 20 ° C / min. The above heating process is essentially a heat treatment process of the precursor, in which lithium and iron and oxygen are combined to form an iron oxide having a certain crystal structure, and at the same time, part of the carbonyl group is carbonized at a high temperature, and coated on the surface of the LFO to form a lithium iron oxide composite. material. Since the carbonyl compound of iron is volatile and decomposes when heated, the difference in heating rate, temperature and holding time will affect the composition of LFO, thereby changing the amount of lithium ion embedded in the LFO, affecting the first coulombic efficiency.

The above-mentioned synthetic lithium ferrite composite material is easy to obtain and the preparation process is simple, thereby reducing the cost of the lithium iron oxide composite material.

The present application also provides a lithium ion battery comprising a positive electrode and a negative electrode, the negative electrode being the lithium iron oxide composite material described in the above scheme or the lithium iron oxide composite material prepared by the preparation method described in the above scheme.

In the lithium ion battery of the present application, the material of the positive electrode is well known to those skilled in the art, and the present application is not particularly limited.

The present invention describes a low cost and scalable chemical process for synthesizing carbon coated LFO nanoparticles as a high performance anode material for LIB. The LFO electrode with pre-embedded Li largely compensates for the Li loss in the first charge and discharge cycle and improves the initial coulombic efficiency; combined with excellent cycle stability, the lithium ferrite composite electrode can be better utilized from Li of the positive electrode. The air and water-stabilized lithium-iron-oxygen composite anode material developed in this study simultaneously solves the inefficiency problem of transition metal oxide-based anode materials and the instability of conventional lithiating agents, and demonstrates the practical application of transition metal oxides. Excellent performance of the negative electrode. Considering Li storage characteristics and low cost, high density, high safety and non-toxicity, the developed lithium iron oxide composite material has great application prospects as the anode material of the next generation LIB.

In order to further understand the present invention, the lithium iron oxide composite material provided by the present invention will be described in detail below with reference to the examples, and the scope of the present invention is not limited by the following examples.

Example 1

In a typical synthesis, iron pentacarbonyl (0) (15.2 mmol, 99.99%, Sigma-Aldrich) was dissolved in 10 ml of ethanol followed by stoichiometric LiOH·H ₂ O (15.2 mmol, 101.5%, Sigma). -Aldrich), the mixture was stirred vigorously overnight to ensure complete reaction, after removal of the remaining insoluble Li ₂ CO ₃ precipitate by filtration, a viscous dark red precursor solution was obtained; the solution was kept at 40 ° C in a tube furnace Ethanol was evaporated under a stream of N ₂ and then heated at 500 ° C (at a heating rate of 10 ° C / min) for 5 hours to obtain a lithium iron oxide composite.

1) Physical property characterization of LFO materials

1 is a set of physical property characterization of a lithium iron oxide composite material prepared in Example 1 of the present invention; FIG. 1a is an XRD pattern of a lithium iron oxide composite material, as shown in FIG. 1a, the product shown is X-ray diffraction (XRD) analysis showed a good crystalline phase consistent with cubic Li ₂ Fe ₂ O ₃ formed by electrochemical insertion with a lattice parameter of a = 0.417 nm.

1b and 1c are low-magnification TEM photographs (proportional size, 200 nm) and high-magnification TEM photographs (proportional size, 10 nm,) of the lithium iron-oxygen composite material prepared in Example 1, respectively, and analyzed by transmission electron microscopy (TEM). Morphology and structure, interconnected nanoparticles with a size of 20-100 nm were observed in Figure 1b, showing single-crystal features and clear lattice fringes at a distance of 0.24 nm in the high-resolution TEM image of Figure 1c, consistent with XRD The pattern is determined by the interplanar spacing of the (111) plane; in addition, it can be seen from Fig. 1c that the LFO nanoparticles are covered by a thin carbon shell with a thickness of about 2 nm and some disordered graphite layers are visible.

Figure 1d is a TGA curve of the lithium iron oxide composite prepared in Example 1, and the presence of carbon was confirmed by thermogravimetric analysis in air; the initial weight loss of the sample below 200 °C is related to the moisture adsorbed on the surface, due to the Fe portion. The oxidation, the weight gradually increases, and then a weight loss of about 8 wt% due to the combustion of carbon.

1e is a Raman spectrum of the lithium iron-oxygen composite material prepared in Example 1, which corresponds to the D (1330 cm ^-1 ) and G (1595 cm ^-1 ) bands of the carbon of the disordered and graphite structure, respectively, D The intensity ratio of the belt to the G belt (I _D /I _G ) was about 0.91, indicating a partial graphite structure. Inductively coupled plasma optical emission spectroscopy (ICP-OES) gave a Li-Fe ratio of 0.55 after synthesis.

1f is an XPS spectrum of the lithium iron-oxygen composite material prepared in the present embodiment, and the oxidation state of Fe is determined by x-ray photoelectron spectroscopy (XPS); the Fe2p _3/2 spectrum can be deconvolved into two peaks, corresponding to 708.3eV Fe ²⁺ and 710.6eV Fe ³⁺ , Fe ²⁺ /Fe ³⁺ molar ratio is 0.51; assuming that the main body of LFO (since the partial oxidation of Fe ²⁺ on the surface should be higher) Fe ²⁺ / The ratio of Fe ^{3+ was} the same, and the nominal composition of the chemically synthesized LFO was determined to be Li _1.03 Fe _1.87 O ₃ .

2) Electrochemical performance of carbon coated LFO nanoparticles

A half cell will be assembled with the Li foil to evaluate the electrochemical performance of the carbon coated LFO nanoparticles. Fe ₂ O ₃ (hematite) nanoparticles were used as reference samples to demonstrate the advantages of the LFO electrode. 2 is an electrochemical performance of a lithium iron-oxygen composite material prepared as an anode material in the present embodiment, and FIG. 2a shows an initial constant current charge-discharge curve of a lithium iron-oxygen composite material and Fe ₂ O ₃ at a current of 100 mAh ⁻¹ . Compared with Fe ₂ O ₃ , lithium-iron-oxygen composites have a lower open circuit voltage (OCV) of about 2.25V; unlike Fe ₂ O ₃ and two-step lithiation, lithium-iron-oxygen composites are only 0.65V ( Vs. Li ⁺ /Li) showed a significant discharge platform with a discharge capacity of 1069 mAh g ^-1 ; in the subsequent delithiation process, the lithium-iron-oxygen composite and Fe ₂ O ₃ have similar voltage curve distributions; The initial capacity is lower, but the first efficiency of the lithium-iron-oxygen composite (about 90%) is significantly higher than that of Fe ₂ O ₃ (about 79%).

The first electrochemical behavior of lithium-iron-oxygen composites and Fe ₂ O ₃ can also be reflected by its cyclic voltammetry (CV) curve (Fig. 3). Figure 3 shows the cyclic volts of lithium-iron-oxygen composites and Fe ₂ O ₃ . The An Curve has a sweep rate of 0.1 mVs ^-1 ; the lithium iron oxide composite of Figure 3 shows only one peak during the first cathode scan. More importantly, the synthetic carbon-coated LFO nanoparticles are very stable when stored in an environment exposed to both air and moisture, as shown in Figure 2b, and Figure 2b shows lithium iron oxide complexes stored at room temperature for different times. Material specific capacity and first efficiency, as can be seen from Figure 2b, the initial charge and discharge capacity and CE remain almost unchanged even after 55 days of storage, highlighting the significant stability and feasibility of its practical application; Sexual characteristics, lithium iron oxide composite electrodes can be fabricated using non-toxic binders and solvents such as sodium alginate and water, respectively.

At the same time, although the precise control of the Li:Fe feed ratio (Fig. 4) and the annealing temperature (Fig. 5) has little effect on the LFO phase, reflecting only the chemical composition and crystallinity, they obtain the best initial CE for the LFO. Play a very important role. Figure 4 is an XRD pattern of lithium-iron-oxygen composites synthesized at different concentrations of LiOH:Fe(CO) ₅ at 500 °C (Fig. 4a) and initial discharge specific capacity, first efficiency diagram (Fig. 4b), lithium iron oxide composite The molar ratio of Li:Fe in the material is greater than 1; Figure 5 is the XRD pattern of the lithium iron oxide composite synthesized under different temperature conditions (Fig. 5a) and the first capacity, coulombic efficiency diagram (Fig. 5b), LiOH: Fe(CO) ₅ molar ratio 1:1.

Figure 2c shows the charge-discharge curves of the LFO electrode at different periods. As can be seen from Figure 2c, the discharge platform shifts to a higher potential of about 1V (vs.Li ⁺ /Li) in the second cycle, and remains stable while charging. The gradual increase in the first 30 cycles means a possible activation process. 2d is a rate performance curve of the lithium iron oxide composite material prepared according to the embodiment and Fe ₂ O ₃ , as shown in FIG. 2d, the lithium iron oxide composite material and Fe are evaluated by constant current charge and discharge at various current densities. ₂ O ₃ ratio of the electrode performance; with Fe ₂ O ₃ rapid decline in electrode capacity Conversely, when the current density increases, the specific capacity of the electrode decreased slightly LFO, and maintained at about 580mAh g ^-1 current 2000mAh g ^-1 , showing very excellent high rate performance. 2e is a cycle stability curve of the lithium iron oxide composite material prepared according to the embodiment and Fe ₂ O ₃ , and the long-term cycle stability is evaluated at a medium current density of 500 mAh g ⁻¹ shown in FIG. 2 e ; the Fe ₂ O ₃ electrode capacity 50 in the previous cycle rapidly decreased to about 150mAh g ^-1, along with the CE lower; contrary, the LFO initial capacity lower electrodes of the display, but to maintain a steady value of about 800mAh g ^-1 100 in the previous cycle, At the end of the 400th cycle, the LFO electrode still retained a reversible capacity of over 700 mAh g ^-1 .

As shown in FIG. 6 , FIG. 6 is a comparison of the electrochemical performance of the lithium iron oxide composite material prepared by the embodiment and Fe ₃ O ₄ , and FIG. 6 a is the first charge and discharge curve of the above two materials as the electrode material, FIG. 6 b and FIG. 6c is the rate performance curve and the cycle stability curve of the above two materials as electrode materials respectively. It can be seen from FIG. 6 that a two-step lithiation process is also observed in the first cycle, resulting in an initial irreversible Li loss exceeding 30%. Fe ₃ O ₄ nanoparticles have better lithium storage properties than Fe ₂ O ₃ nanoparticles, but their performance is still poor compared to carbon-coated LFO nanoparticles. The above comparison highlights the superior electrochemical characteristics of carbon-coated LFO nanoparticles, unlike the simple binary TMO.

3) Full-cell electrochemical performance based on carbon-coated LFO nanoparticles

To demonstrate the feasibility of using carbon-coated LFO nanoparticles in LIB's full cell, the LFO anode was used to match their commercial LiCoO ₂ (LCO) anodes to their initial capacities. Since the negative electrode is the only source of Li in the full cell, any irreversible trapping of Li in the negative electrode will reduce the reversible capacity of the positive electrode. 7 is a graph showing the electrochemical performance of the lithium-iron-oxygen composite material prepared in the present embodiment and the Fe ₂ O ₃ as a negative electrode; FIG. 7a is the first charge-discharge curve of the above two full-cell batteries at a current of 30 mAg ^-1 , As can be seen from Fig. 7a, the charging voltage platform of the LCO-LFO battery is 3.1V, and the slope discharge platform is about 2.3V. For the LCO positive electrode, a discharge capacity of 121 mAh g ^-1 was obtained in the first cycle, which is about 93% of the Li capacity of the LCO positive electrode in the half cell (Fig. 8); conversely, the LCO positive electrode in the LCO-Fe ₂ O ₃ battery Since a large amount of Li was trapped in the Fe ₂ O ₃ negative electrode, a smaller discharge capacity was exhibited as 98 mAh g ^-1 . As shown in FIG. 7b, FIG. 7b is a charge and discharge curve of the whole battery prepared by the above lithium iron-oxygen composite material in different cycles. Since the lithium ion potential of the LFO negative electrode moves upward, the discharge platform slightly moves to a lower voltage, and the discharge voltage curve It usually remains the same, indicating that the current full battery system has good reversibility.

Figure 7c depicts the cycle stability of a full cell; the LCO-LFO cell maintains a reversible capacity of about 100 mAh·g ^-1 after cycling for 60 cycles at a constant current density of 30 mA·g ^-1 , at such lower current densities At the end of the test, the stability of the LCO-Fe ₂ O ₃ battery was slightly lower, and the capacity was lower at 53 mAh·g ^-1 . As shown in FIG. 7d, FIG. 7d is a graph showing the rate performance of the above two full cells, which uses the increased current density to evaluate the full capacity of the battery; as shown in FIG. 7d, when the current density is increased, the LCO-LFO battery exhibit good stability and a small decrease in capacity, retention capacity of approximately 90mAh · g ^-1 at a current of 200mA · g ^-1; although exhibited similar stability, but since the negative electrode Fe ₂ O ₃ Li is captured in large quantities, so the capacity of the LCO-Fe ₂ O ₃ battery is much lower.

Example 2

Iron pentacarbonyl (0) (10 mmol, 99.99%, Sigma-Aldrich) was dissolved in 10 ml of ethanol, then stoichiometric LiOH.H ₂ O (5 mmol, 101.5%, Sigma-Aldrich) was added and the mixture was stirred vigorously overnight. To ensure complete reaction, the remaining insoluble Li ₂ CO ₃ precipitate was removed by filtration to obtain a viscous dark red precursor solution; the solution was kept at 40 ° C, and the ethanol was evaporated in a tube furnace under a stream of N ₂ , and then Heating at 300 ° C (at a heating rate of 10 ° C / min) for 5 hours, to obtain a lithium iron oxide composite; its carbon layer thickness is 2.40 nm, the molecular formula of the carbon layer coated lithium iron oxide is Li _0.51 Fe _1.9 O ₃ .

Example 3

Dissolve the mixture with hexacarbonyldiiron (0) (12 mmol, 99.99%, Sigma-Aldrich) in 10 ml of ethanol, then add stoichiometric LiOH·H ₂ O (8.04 mmol, 101.5%, Sigma-Aldrich). Overnight to ensure complete reaction, after removal of the remaining insoluble Li ₂ CO ₃ precipitate by filtration, a viscous dark red precursor solution was obtained; the solution was kept at 40 ° C, and the ethanol was evaporated under a stream of N ₂ in a tube furnace. Then, it was heated at 300 ° C (at a heating rate of 10 ° C / min) for 8 hours to obtain a lithium iron-oxygen composite material; the carbon layer thickness was 2.40 nm, and the molecular formula of the carbon layer-coated lithium iron oxide was Li _0.62 Fe. _1.9 O ₃ .

Example 4

Iron pentacarbonyl (0) (15.2 mmol, 99.99%, Sigma-Aldrich) was dissolved in 10 ml of ethanol, then stoichiometric LiOH·H ₂ O (15.2 mmol, 101.5%, Sigma-Aldrich) was added, and the mixture was vigorously Stir overnight to ensure complete reaction, after removing the remaining insoluble Li ₂ CO ₃ precipitate by filtration, to obtain a viscous dark red precursor solution; maintaining the solution at 40 ° C, evaporating the ethanol in a tube furnace under a stream of N ₂ And then heating at 300 ° C (at a heating rate of 10 ° C / min) for 6 hours to obtain a lithium iron oxide composite material; its carbon layer thickness is 2.35 nm, the molecular formula of the carbon layer coated lithium iron oxide is Li _1.05 Fe _1.86 O ₃ .

Example 5

Tridecacarbonyl triiron (0) (16 mmol, 99.99%, Sigma-Aldrich) was dissolved in 10 ml of ethanol, then stoichiometric LiOH·H ₂ O (48 mmol, 101.5%, Sigma-Aldrich) was added and the mixture was vigorously stirred. Overnight to ensure complete reaction, after removal of the remaining insoluble Li ₂ CO ₃ precipitate by filtration, a viscous dark red precursor solution was obtained; the solution was kept at 40 ° C, and the ethanol was evaporated under a stream of N ₂ in a tube furnace. Then, it was heated at 300 ° C (at a heating rate of 10 ° C / min) for 5 hours to obtain a lithium iron oxide composite material; the carbon layer thickness was 2.2 nm, and the molecular formula of the carbon layer coated lithium iron oxide was Li _1.1 Fe. _1.9 O ₃ .

Example 6

Iron pentacarbonyl (0) (16 mmol, 99.99%, Sigma-Aldrich) was dissolved in 10 ml of ethanol, then stoichiometric LiOH.H ₂ O (64 mmol, 101.5%, Sigma-Aldrich) was added and the mixture was stirred vigorously overnight. To ensure complete reaction, the remaining insoluble Li ₂ CO ₃ precipitate was removed by filtration to obtain a viscous dark red precursor solution; the solution was kept at 40 ° C, and the ethanol was evaporated in a tube furnace under a stream of N ₂ , and then Heating at 300 ° C (at a heating rate of 10 ° C / min) for 5 hours, to obtain a lithium iron oxide composite material; the carbon layer thickness is 1.5 nm, the molecular formula of the carbon layer coated lithium iron oxide is Li _1.1 Fe _1.87 O ₃ .

Example 7

Iron pentacarbonyl (0) (14.3 mmol, 99.99%, Sigma-Aldrich) was dissolved in 10 ml of ethanol, then stoichiometric LiOH·H ₂ O (14.3 mmol, 101.5%, Sigma-Aldrich) was added, and the mixture was vigorously Stir overnight to ensure complete reaction, after removing the remaining insoluble Li ₂ CO ₃ precipitate by filtration, to obtain a viscous dark red precursor solution; maintaining the solution at 40 ° C, evaporating the ethanol in a tube furnace under a stream of N ₂ And then heating at 500 ° C (at a heating rate of 10 ° C / min) for 6 hours to obtain a lithium iron oxide composite material; its carbon layer thickness is 2 nm, the molecular formula of the carbon layer coated lithium iron oxide is Li _1.03 Fe _1.82 O ₃ .

Example 8

Iron pentacarbonyl (0) (14.3 mmol, 99.99%, Sigma-Aldrich) was dissolved in 10 ml of ethanol, then stoichiometric lithium bicarbonate (14.3 mmol, Sigma-Aldrich) was added and the mixture was stirred vigorously overnight to ensure completeness The reaction, after removing the remaining insoluble Li ₂ CO ₃ precipitate by filtration, to obtain a viscous dark red precursor solution; maintaining the solution at 40 ° C, evaporating the ethanol in a tube furnace under a stream of N ₂ , and then at 500 ° C Heating (at a heating rate of 10 ° C / min) for 8 hours gave a lithium iron oxide composite material; the carbon layer thickness was 1.9 nm, and the carbon layer coated lithium iron oxide had a molecular formula of Li _1.03 Fe _1.82 O ₃ .

Example 9

Iron pentacarbonyl (0) (15.2 mmol, 99.99%, Sigma-Aldrich) was dissolved in 10 ml of ethanol, then stoichiometric lithium nitrate (45.6 mmol, Sigma-Aldrich) was added and the mixture was stirred vigorously overnight to ensure complete reaction. After removing the remaining insoluble Li ₂ CO ₃ precipitate by filtration, a viscous dark red precursor solution was obtained; the solution was kept at 40 ° C, and the ethanol was evaporated in a tube furnace under a stream of N ₂ , and then at 400 ° C ( Heating at a heating rate of 10 ° C / min for 3 hours gave a lithium iron oxide composite material; the carbon layer thickness was 1.6 nm, and the carbon layer coated lithium iron oxide had a molecular formula of Li _0.5 Fe _1.9 O ₃ .

Example 10

Iron pentacarbonyl (0) (15.2 mmol, 99.99%, Sigma-Aldrich) was dissolved in 10 ml of ethanol, then stoichiometric LiOH.H ₂ O (45.6 mmol, 101.5%, Sigma-Aldrich) was added and the mixture was vigorously Stir overnight to ensure complete reaction, after removing the remaining insoluble Li ₂ CO ₃ precipitate by filtration, to obtain a viscous dark red precursor solution; maintaining the solution at 40 ° C, evaporating the ethanol in a tube furnace under a stream of N ₂ Then, heating at 600 ° C (at a heating rate of 10 ° C / min) for 5 hours to obtain a lithium iron oxide composite material; the carbon layer thickness is 1.9 nm, and the molecular formula of the carbon layer coated lithium iron oxide is Li _0.97 Fe _1.82 O ₃ .

Example 11

Iron pentacarbonyl (0) (15.2 mmol, 99.99%, Sigma-Aldrich) was dissolved in 10 ml of ethanol, then stoichiometric LiOH.H ₂ O (15.2 mmol, 101.5%, Sigma-Aldrich) was added and the mixture was vigorously Stirring overnight to ensure complete reaction, after removing the remaining insoluble Li ₂ CO ₃ precipitate by filtration, a viscous dark red precursor solution was obtained; the solution was kept at 40 ° C, and the ethanol was evaporated under a N ₂ stream in a tube furnace. Then, heating at 700 ° C (at a heating rate of 10 ° C / min) for 5 hours to obtain a lithium iron oxide composite material; the carbon layer thickness is 1.8 nm, and the molecular formula of the carbon layer coated lithium iron oxide is Li _0.8 Fe _1.82 O ₃ .

Example 12

Iron pentacarbonyl (0) (8.4 mmol, 99.99%, Sigma-Aldrich) was dissolved in 10 ml of ethanol, then stoichiometric LiOH·H ₂ O (5.63 mmol, 101.5%, Sigma-Aldrich) was added and the mixture was vigorously Stir overnight to ensure complete reaction, after removing the remaining insoluble Li ₂ CO ₃ precipitate by filtration, to obtain a viscous dark red precursor solution; maintaining the solution at 40 ° C, evaporating the ethanol in a tube furnace under a stream of N ₂ And then heating at 800 ° C (at a heating rate of 10 ° C / min) for 5 hours to obtain a lithium iron oxide composite material; the carbon layer thickness of 1.8 nm, the molecular formula of the carbon layer coated lithium iron oxide is Li _0.6 Fe _1.82 O ₃ .

Example 13

Iron pentacarbonyl (0) (8.4 mmol, 99.99%, Sigma-Aldrich) was dissolved in 10 ml of ethanol, then stoichiometric lithium nitrate (4.2 mmol, Sigma-Aldrich) was added and the mixture was stirred vigorously overnight to ensure complete reaction. After removing the remaining insoluble Li ₂ CO ₃ precipitate by filtration, a viscous dark red precursor solution was obtained; the solution was kept at 40 ° C, and the ethanol was evaporated in a tube furnace under a stream of N ₂ , and then at 600 ° C ( Heating at a heating rate of 10 ° C / min for 8 hours gave a lithium iron oxide composite material; the carbon layer thickness was 2.4 nm, and the carbon layer coated lithium iron oxide had a molecular formula of Li _0.92 Fe _1.7 O ₃ .

Example 14

Iron pentacarbonyl (0) (13.6 mmol, 99.99%, Sigma-Aldrich) was dissolved in 10 ml of ethanol, then stoichiometric LiOH.H ₂ O (34 mmol, 101.5%, Sigma-Aldrich) was added and the mixture was stirred vigorously. Overnight to ensure complete reaction, after removal of the remaining insoluble Li ₂ CO ₃ precipitate by filtration, a viscous dark red precursor solution was obtained; the solution was kept at 40 ° C, and the ethanol was evaporated under a stream of N ₂ in a tube furnace. Then, heating at 400 ° C (at a heating rate of 10 ° C / min) for 8 hours to obtain a lithium iron oxide composite material; the carbon layer thickness is 1.55 nm, and the molecular formula of the carbon layer coated lithium iron oxide is Li _0.95 Fe _1.7 O ₃ .

Example 15

Iron pentacarbonyl (0) (13.6 mmol, 99.99%, Sigma-Aldrich) was dissolved in 10 ml of ethanol, then stoichiometric LiOH·H ₂ O (45.6 mmol, 101.5%, Sigma-Aldrich) was added, and the mixture was vigorously Stir overnight to ensure complete reaction, after removing the remaining insoluble Li ₂ CO ₃ precipitate by filtration, to obtain a viscous dark red precursor solution; maintaining the solution at 40 ° C, evaporating the ethanol in a tube furnace under a stream of N ₂ Then, heating at 600 ° C (at a heating rate of 10 ° C / min) for 3 hours to obtain a lithium iron oxide composite material; the carbon layer thickness is 1.55 nm, and the molecular formula of the carbon layer coated lithium iron oxide is Li _0.53 Fe _1.9 O ₃ .

The above description of the embodiments is merely to assist in understanding the method of the present invention and its core idea. It should be noted that those skilled in the art can make various modifications and changes to the present invention without departing from the spirit and scope of the invention.

The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments are obvious to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but the scope of the invention is to be accorded

Claims (10)

1. A lithium iron oxide composite material comprising a lithium iron oxide as shown in formula (I) and a carbon layer coated on a surface of the lithium iron oxide;

   Li _x Fe _y O ₃ (I);

   Where x is greater than 0 and less than or equal to 1.2;

   y is 1.5 to 2.
2. The lithium iron-oxygen composite according to claim 1, wherein the carbon layer has a thickness of 1.5 to 2.5 nm.
3. The lithium iron-oxygen composite according to claim 1, wherein said x is from 0.5 to 1.1, and said y is from 1.7 to 1.9.
4. The lithium iron oxide composite according to claim 1, wherein the lithium iron oxide composite has a size of 20 to 100 nm.
5. A method for preparing a lithium iron oxide composite material according to claim 1, comprising the steps of:

   The carbonyl-containing iron-based compound is reacted with a lithium source in a solvent to obtain a precursor solution;

   The precursor solution is heated to obtain a lithium iron oxide composite material.
6. The method according to claim 5, wherein the carbonyl group-containing iron-based compound is one or more selected from the group consisting of iron pentacarbonyl, hexacarbonyldiiron, and tridecacarbonyltriiron; The source is selected from one or more of lithium hydroxide, lithium hydrogencarbonate, lithium nitrate, and lithium carbonate.
7. The process according to claim 5, wherein the molar ratio of the iron-based compound to the lithium source is (10 to 20): (5 to 76).
8. The preparation method according to claim 5, wherein the heating is performed under a flow of N ₂ , the heating temperature is 300 to 1000 ° C, the heating time is 0 to 10 h, and the heating rate is increased. It is 10 to 20 ° C / min.
9. The process according to claim 5, wherein the temperature of the precursor solution is 40 to 50 ° C before heating.
10. A lithium ion battery comprising a positive electrode and a negative electrode, wherein the material of the negative electrode is the lithium iron oxide composite material according to any one of claims 1 to 4 or the preparation according to any one of claims 5 to 9. The lithium iron oxide composite material prepared by the method.

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