CN109817927B

CN109817927B - Lithium battery positive electrode material capable of improving SOC estimation precision and preparation method thereof

Info

Publication number: CN109817927B
Application number: CN201910074874.4A
Authority: CN
Inventors: 马振; 李庆余; 周德清; 王龙超; 崔李三; 张翔; 耿斌; 向明祥; 朱正中
Original assignee: Anhui Yijiatong Battery Co ltd
Current assignee: Anhui Yijiatong Battery Co ltd
Priority date: 2019-01-25
Filing date: 2019-01-25
Publication date: 2022-03-25
Anticipated expiration: 2039-01-25
Also published as: CN109817927A

Abstract

The invention discloses a lithium battery anode material capable of improving SOC estimation precision and a preparation method thereof, wherein the lithium battery anode material comprises 80-90 wt% of lithium iron phosphate and 2-10 wt% of lithium iron silicate. The method for synthesizing the cathode material is simple, the process is easy to control, the material structure is stable, compared with the existing lithium iron phosphate cathode material, the particle size of the material tends to the nano degree, the discharge voltage curve of the material has a slope trend, and the voltage change trend provides a powerful basis for accurately estimating the SOC of the battery management system on the premise of not influencing the original specific discharge capacity and cycle performance of the lithium iron phosphate cathode material.

Description

Lithium battery positive electrode material capable of improving SOC estimation precision and preparation method thereof

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a lithium battery positive electrode material capable of improving SOC estimation precision and a preparation method thereof.

Background

In recent years, power batteries have attracted much attention as an important link in the development of new energy automobiles. The lithium iron phosphate anode material becomes the first choice of the anode material of the power lithium ion battery due to the advantages of relatively low price, environmental friendliness, good safety, long cycle life and the like, and the lithium iron phosphate battery is increasingly applied to energy storage systems. In order to ensure the cycle performance and safety of the lithium iron phosphate battery, the battery management system is required to estimate the SOC more accurately. However, in the current prior art, the discharging platform of the lithium iron phosphate positive electrode material is relatively flat, so that the battery voltage and the SOC have a nonlinear relationship, and a battery management system has great trouble in estimating the SOC.

At present, many achievements are made in domestic and foreign research on SOC estimation, including a Kalman filtering method, an ampere-hour integration method, a neural network method and the like, and although the methods can improve the SOC estimation precision of a battery management system, the methods have the problems of large workload, complex operation, large error and the like.

Disclosure of Invention

The invention aims to solve the technical problems in the prior art. Therefore, the invention provides the lithium battery positive electrode material capable of improving the SOC estimation precision and the preparation method thereof, the discharge voltage curve of the positive electrode material has a slope trend, and the voltage change trend provides a powerful basis for the accurate estimation of the SOC of the battery management system on the premise of not influencing the original discharge specific capacity and cycle performance of the lithium iron phosphate positive electrode material.

In order to achieve the purpose, the invention adopts the technical scheme that:

the lithium battery anode material capable of improving the SOC estimation precision comprises 80-90 wt% of lithium iron phosphate and 2-10 wt% of lithium iron silicate.

The particles of the lithium battery positive electrode material are spherical, and the particle size is 50-300 nm.

The invention also provides a preparation method of the lithium battery positive electrode material capable of improving the SOC estimation precision, which comprises the following steps:

step one, preparing a surfactant solution;

step two, mixing lithium iron phosphate and lithium iron silicate according to the mass ratio of 20: 1-10: 1, and adding the mixture into the surfactant solution prepared in the step one;

step three, stirring the mixed solution obtained in the step two until the mixed solution completely reacts, and then drying the mixed solution;

and step four, performing solid phase sintering on the dried mixture obtained in the step three to obtain the lithium iron phosphate/lithium iron silicate composite lithium battery anode material.

Preferably, the method for preparing the surfactant solution in the first step is to dissolve the surfactant in deionized water and mix the dissolved surfactant and the deionized water uniformly at the temperature of 40-80 ℃, wherein the mass volume ratio of the surfactant to the deionized water is 0.001-0.01 g: 20-80 mL.

The surfactant in the first step is a span surfactant.

The span surfactant is any one or combination of span-20, span-40, span-60 and span-80.

And the mixing and stirring time in the third step is 8-14 h.

And the solid phase sintering condition in the fourth step is that under the protection of inert gas, the temperature is raised to 650-800 ℃ at the heating rate of 5-10 ℃/min, and the temperature is kept for 3-6 h.

The inert gas is argon.

The invention has the beneficial effects that: the lithium battery anode material prepared by the invention is a composite material, the particle size of the composite material tends to the nano degree, the voltage of the composite material is maintained at 3.4V along with the reduction of SOC, but when the SOC reaches about 0.3-0.4, namely the residual capacity is 30-40%, the voltage of the battery starts to reduce, the discharge voltage curve of the battery starts to have a slope trend, and the voltage change trend provides a powerful basis for the accurate estimation of the SOC of a battery management system on the premise of not influencing the original discharge specific capacity and cycle performance of the lithium iron phosphate anode material, so that the problems of large workload, complex operation, large error and the like in the conventional SOC estimation method are solved to a certain extent, and the anode material has the advantages of simple synthesis method, easy process control and stable material structure.

Drawings

The description includes the following figures, the contents shown are respectively:

fig. 1 is a Scanning Electron Microscope (SEM) image of the lithium iron phosphate/lithium iron silicate composite lithium battery positive electrode material prepared in embodiment 1 of the present invention at different magnifications;

fig. 2 is an X-ray diffraction (XRD) pattern of the lithium iron phosphate/lithium iron silicate composite lithium battery positive electrode material prepared in example 1 of the present invention;

fig. 3 is an X-ray photoelectron spectroscopy (XPS) chart of the lithium iron phosphate/lithium iron silicate composite lithium battery positive electrode material prepared in example 1 of the present invention;

fig. 4 is a comparison graph of SOC variation with voltage between the lithium battery positive electrode material prepared in examples 1, 2, and 3 of the present invention and the conventional lithium iron phosphate positive electrode material.

Detailed Description

The following detailed description of the embodiments of the present invention will be given with reference to the accompanying drawings for a purpose of helping those skilled in the art to more fully, accurately and deeply understand the concept and technical solution of the present invention and to facilitate its implementation.

Example 1

A preparation method of a lithium battery positive electrode material capable of improving SOC estimation precision comprises the following steps:

step one, 0.005g of span80 was weighed and dissolved in 50mL of deionized water to make a homogeneous mixed solution at 60 ℃.

And secondly, weighing 0.9524g of lithium iron phosphate and 0.0476g of lithium iron silicate respectively, and sequentially adding the weighed materials into the mixed solution prepared in the first step.

And step three, stirring the mixed solution obtained in the step two for 12 hours, and then putting the mixed solution into an oven for drying.

Step four, mixing the dried mixture obtained in the step threePlacing the material in a burning boat (under the protection of argon), carrying out high-temperature solid phase sintering, raising the temperature to 650 ℃ at the heating rate of 5 ℃/min, and preserving the heat for 4h at the temperature to prepare the lithium iron phosphate/lithium iron silicate composite lithium battery anode material. Scanning Electron Microscope (SEM) images of the composite material prepared in the embodiment under different magnifications are shown in figure 1, and it can be seen from the figure that the size distribution of the composite material is relatively uniform, and the size of particles is 50-300 nm; the X-ray diffraction (XRD) spectrum of the composite material prepared by the embodiment is shown in figure 2, and the crystal structure of the prepared product is good; the X-ray photoelectron spectroscopy (XPS) spectrum of the composite material prepared in this example is shown in FIG. 3, and it can be seen from the graph that when the binding energy is 100.8eV, a characteristic peak of Si 2p appears corresponding to tetravalent silicon element, which proves that [ SiO ] is formed in the composite material₄]The orthosilicate structure of (a) indicates the presence of lithium iron silicate in the composite material.

Example 2

step one, 0.008g of span40 was weighed and dissolved in 70mL of deionized water to prepare a uniform mixed solution at 80 ℃.

And step two, respectively weighing 0.9375g of lithium iron phosphate and 0.0625g of lithium iron silicate, and sequentially adding the weighed materials into the mixed solution prepared in the step one.

And step three, stirring the mixed solution obtained in the step two for 10 hours, and then putting the mixed solution into an oven for drying.

And step four, placing the mixture dried in the step three in a burning boat (under the protection of argon gas), performing high-temperature solid phase sintering, raising the temperature to 700 ℃ at the heating rate of 10 ℃/min, and preserving the heat for 5 hours at the temperature to prepare the lithium iron phosphate/lithium iron silicate composite lithium battery anode material.

Example 3

step one, 0.003g of span60 was weighed and dissolved in 40mL of deionized water to make a homogeneous mixed solution at 50 ℃.

And secondly, weighing 0.9091g of lithium iron phosphate and 0.0909g of lithium iron silicate respectively, and sequentially adding the weighed materials into the mixed solution prepared in the first step.

And step three, stirring the mixed solution obtained in the step two for 8 hours, and then putting the mixed solution into an oven for drying.

And step four, placing the mixture dried in the step three in a burning boat (under the protection of argon), performing high-temperature solid phase sintering, raising the temperature to 750 ℃ at the heating rate of 8 ℃/min, and preserving the heat for 3 hours at the temperature to prepare the lithium iron phosphate/lithium iron silicate composite lithium battery anode material.

The positive electrode composite materials prepared in the

embodiments

1, 2 and 3 of the invention are respectively made into button cells, the lithium battery is taken as a test object, an LANG-BT-2013A type blue battery test system is adopted to perform SOC-OCV test on the test object, the test current is 500mA/g, the test voltage range is 2.0-3.9V, the change of the measured battery SOC along with the voltage is shown in figure 1, the horizontal axis in the figure 1 is a battery SOC digital axis, the vertical axis in the figure 1 is a battery voltage digital axis, the

curves

1, 2 and 3 in the figure 1 respectively correspond to the discharge voltage curves measured by the button cells made of the composite materials prepared in the

embodiments

1, 2 and 3, and the curve 4 in the figure 1 is a discharge voltage curve measured by the button cells made of the conventional lithium iron phosphate positive electrode material. It can be seen from the figure that the composite material voltage is maintained at 3.4V with the decrease of SOC, but when the SOC reaches about 0.3-0.4, that is, the remaining capacity is 30-40%, the battery voltage starts to decrease, and the discharge voltage curve has a slope trend, which provides a powerful basis for the accurate estimation of the SOC of the battery management system on the premise of not affecting the original specific discharge capacity and cycle performance of the lithium iron phosphate anode material.

The invention is described above with reference to the accompanying drawings. It is to be understood that the specific implementations of the invention are not limited in this respect. Various insubstantial improvements are made by adopting the method conception and the technical scheme of the invention; the present invention is not limited to the above embodiments, and can be modified in various ways.

Claims

1. The preparation method of the lithium battery anode material capable of improving the SOC estimation precision is characterized in that the lithium battery anode material comprises 80-90 wt% of lithium iron phosphate and 2-10 wt% of lithium iron silicate;

the preparation method comprises the following steps:

step one, preparing a surfactant solution;

step four, sintering the dried mixture obtained in the step three in a solid phase manner to obtain a lithium iron phosphate/lithium iron silicate composite lithium battery anode material;

the surfactant in the first step is a span surfactant;

and the mixing and stirring time in the third step is 8-14 h.

2. The method of claim 1, wherein the particles of the lithium battery positive electrode material are spherical and have a particle size of 50-300 nm.

3. The method for preparing the lithium battery positive electrode material capable of improving the SOC estimation accuracy according to claim 1, wherein the method for preparing the surfactant solution in the step one is to dissolve the surfactant in deionized water and mix the dissolved surfactant and the deionized water uniformly at a temperature of 40-80 ℃, wherein a mass-to-volume ratio of the surfactant to the deionized water is 0.001-0.01 g: 20-80 mL.

4. The method for preparing a lithium battery positive electrode material capable of improving SOC estimation accuracy according to claim 3, wherein the span-based surfactant is any one or more of span-20, span-40, span-60 and span-80.

5. The method for preparing a lithium battery cathode material capable of improving SOC estimation accuracy as claimed in claim 1, wherein the solid phase sintering in the fourth step is performed under the protection of inert gas at a temperature rising rate of 5-10 ℃/min to 650-800 ℃, and the temperature is maintained for 3-6 h.

6. The method of claim 5, wherein the inert gas is argon.