CN105571963A - Characterization method for hardness of electrode materials under combined action of electrochemistry and substrate effects - Google Patents

Abstract

The invention discloses a characterization method for hardness of electrode materials under the combined action of electrochemistry and substrate effects. The method includes the steps that a charging and discharging test is conducted on the electrode materials of a lithium ion battery to obtain the electrode materials in different charging and discharging states, and an indentation experiment is conducted on the electrode materials through an indentation tester to obtain an indentation load displacement curve, so that the composite hardness between the electrode materials and a substrate is extracted under a certain charging and discharging state, and finally the composite hardness is substituted into a constructed analytic theoretical model between the hardness and the indentation size to obtain the hardness of the electrode materials. The hardness of the electrode materials of the lithium ion battery in different charging and discharging states can be successfully extracted by using the analytic theoretical model obtained through the method, and the characterization method is convenient, fast and beneficial for large-scale engineering application.

Description

The characterizing method of a kind of galvanochemistry and substrate effect acting in conjunction lower electrode material hardness

Technical field

The present invention relates to the characterizing method of a kind of galvanochemistry and substrate effect acting in conjunction lower electrode material hardness, belong to energy and material mechanical property characterization research field.

Background technology

Lithium ion battery has that high-energy-density, high power density, security performance are good, the advantage such as have extended cycle life, and containing polluters such as lead, cadmium, mercury, is a kind of ideal energy storage device.Negative material, as one of the core component of lithium ion battery, has material impact to raising capacity of lithium ion battery and cycle life, has obtained showing great attention to of academia and industrial community.The negative material of suitability for industrialized production is carbon class material, and its theoretical specific capacity is 372mAhg ^-1, the Carbon anode capacity of current practical application closely its theoretical specific capacity, the possibility improving this material specific capacity is further little.With social progress and scientific and technical development, electric automobile is contour needs the requirement of energy equipment to lithium ion battery more and more higher, and the capacity of existing lithium ion battery can not meet the demand of contemporary electronic industry.Therefore, the electrode material seeking high-energy-density becomes the main target of present material worker.

Current, many high-capacity electrode materials have become the focus of scientist's research, such as Si, Sn, Ge etc. and their oxide material [Nature414,359 (2001); Nat.Nanotechnol.3,31 (2008); J.Am.Ceram.Soc.125,5652 (2003); NanoLett.9,3370 (2009); ACSNano6,1522 (2012)], these materials significantly can promote capacity and the energy density of lithium ion battery.But, in charge and discharge process, the repeatedly deintercalation of lithium ion in electrode material, huge cubic deformation can be caused, up to 300%, finally cause electrode material failure damage, and then cause decline [NanoLett.11,2962 (2011) of cycle performance of lithium ion battery; Science342,716 (2013); ACSNano9,5299 (2015); Phys.Rev.Lett.107,045503 (2011); EnergyEnviron.Sci.4,3844 (2011); J.Mater.Chem.A2,1128 (2014)].

Recently, by a large amount of in-situ observation technology, the dynamic process that lithium ion spreads in electrode material is able to Real-Time Monitoring, thus has found a large amount of dislocations because electrochemical reaction causes.These dislocations can alleviate the enormousness distortion of electrode material in charge and discharge process to a great extent, can be reached the situation improved electrode material and destroy by plastic yield.Since there has been dislocation, we consider, hardness is the macroreaction of material based on dislocation theory, can the electricity of electrode material be extracted by the method for hardness test? the develop rapidly of Nanoindentation is that the research carrying out material mechanical performance provides strong instrument, calendar year 2001, the dimensional analysis such as Dao, finite element combining nano indentation test, establish contacting between indentation load displacement curve and the elastic plastic mechanical properties of material.In conjunction with effective checking of uniaxial tensile test, a Xu Kewei teach problem group indentation load displacement curve obtains yield strength and the hardenability value of Al film, and is obtained the yield strength of Cu film by X-ray diffraction technology by four-point bending method.But, usually can run into the smaller situation of thin-film electrode material thickness in Indentation Process, at this moment will there is substrate (collector) effect to the impact of load-displacement curves, thus cause net result to occur gross differences.Scientist, by introducing substrate effect, successfully establishes membraneous material in analytic model [Surf.Coat.Technol.99,171 (1998) of considering to characterize in substrate effect situation hardness; Surf.Coat.Technol.139,63 (2001)].At present, the characterizing method of hardness under galvanochemistry and the acting in conjunction of substrate effect is not also considered in the world.

Summary of the invention

For the problems referred to above, the object of the invention is to be to provide a kind of analytic model by setting up, directly can calculate the characterizing method of the Composite hardness of lithium ion battery electrode material under different charging and discharging state, for the Evaluating Mechanical Properties of electrode material provides Important Theoretic Foundation.

In order to realize above-mentioned technical purpose, the invention provides the characterizing method of a kind of galvanochemistry and substrate effect acting in conjunction lower electrode material hardness, first the method carries out charge-discharge test to lithium ion battery electrode material, obtain the electrode material under different charging and discharging state, then by impression instrument, indentation test is carried out to electrode material, obtain indentation load displacement curve, thus extract the composite hardness of certain charging and discharging state lower electrode material and substrate, finally be updated to the hardness of foundation and the analytic theory model of impression size, the hardness of electrode material can be obtained, specifically comprise the following steps:

(1) utilizing Fick law, consider boundary condition and starting condition, by solving diffusion equation, drawing electrode material diverse location and the distribution of the lithium concentration not in the same time under state;

(2) by the CONCENTRATION DISTRIBUTION of t, integration is carried out to each position, namely obtain electrode material electricity SOC in this condition;

(3) based in charge and discharge process, can there is cubic deformation thus cause a large amount of dislocation in electrode material, be namely defined as electrochemical induce dislocation EID, the average density of electrochemical induce dislocation wherein, ρ ' _efor the electrochemical induce dislocation desity in certain moment distributes, h is depth of cup, and V is press-in volume;

(4), based on dislocation theory, in Indentation Process, total dislocation of hardness is affected wherein, ρ _sfor electrode material statistics itself stores dislocation, have nothing to do with electrochemical process, α, μ and b are respectively material empirical constant, modulus of shearing and Burgers vector;

(5) according to relation σ=M τ, the H=3 σ of mean stress and hardness, wherein, M is Taylor orientation factor, obtains electrode material hardness H _fand the quantitative resolution relation between SOC: $\frac{H_F}{H_{F0}}=\sqrt{1+\frac{h_e^{*}}{L_0}\mathrm{\Φ}};$

Wherein, $h_e^{*}=\frac{27}{4}\frac{M^2{\mathrm{\α}}^{2}b}{\tan \mathrm{\θ}}{\left(\frac{\mathrm{\μ}}{H_0}\right)}^2{\mathrm{\φc}}_0$ For the galvanochemistry factor,

Electricity controlling elements $\mathrm{\Φ}=\[cos\[\frac{\mathrm{\π}\mathrm{\β}}{2}\]+(\frac{\mathrm{\π}\mathrm{\β}}{4}-\frac{2}{\mathrm{\π}\mathrm{\β}})sin\[\frac{\mathrm{\π}\mathrm{\β}}{2}\]\]\frac{(1-SOC)}{(1+\mathrm{\η}SOC){\mathrm{\β}}^2},$

Opposing indentations degree of depth β=h/L, η is volume expansivity,

The Composite hardness of thin-film electrode material with the filled state that charges for reference, i.e. SOC=1;

(6) (5) analytic relationship is introduced substrate effect, by the composite hardness of test electrode material and substrate, namely obtain the hardness of electrode material.

Preferred scheme is the circular cone pressure head of θ based on two-dimensional film electrode material and semi-cone angle, show that the lithium concentration of two-dimensional film electrode material distributes by step (1):

$c=c_0\[1-{\mathrm{\Σ}}_{n=0}^{\mathrm{\∞}}\frac{4{(-1)}^n}{(2n+1)\mathrm{\π}}\exp \[-\frac{{\mathrm{Dt\π}}^2{(2n+1)}^2}{4L^2}\]cos\[\frac{(2n+1)\mathrm{\π}x}{2L}\]\]$

Wherein,

C ₀for maximum lithium concentration,

D is coefficient of diffusion,

L is the two-dimensional film electrode material thickness of t.

Preferred scheme, in step (2)

Preferred scheme, composite hardness wherein, H _sfor substrate hardness, κ is the dimensionless group of impression response modes, and χ is the dimensionless group of deformation geometry pattern;

The hardness of thin-film electrode material under different state of charge is substituted into composite hardness expression formula, obtains $H_C=H_S+\frac{H_{F0}\sqrt{1+\frac{h_e^{*}}{L_0}\mathrm{\Φ}}-H_S}{1+{\mathrm{\κ\β}}^{\mathrm{\χ}}}.$

More preferably scheme, from in can obtain electrode material Composite hardness H _f0with the hardness H of substrate _sand be used for characterizing SOC.

Method of the present invention mainly carries out indentation test by impression instrument to electrode material, obtains indentation load displacement curve, and the composite hardness calculated is brought into set up analytic model, finally obtains the Composite hardness of electrode material.

Hinge structure, the Advantageous Effects that technical scheme of the present invention is brought:

(1) technical scheme of the present invention proposes first, by impression instrument, indentation test is carried out to electrode material, obtain indentation load displacement curve, the composite hardness calculated is brought into set up analytic model, in order to directly to calculate the Composite hardness of lithium ion battery electrode material under different charging and discharging state, the Evaluating Mechanical Properties for electrode material provides an Important Theoretic Foundation method.

(2) method of the present invention is very convenient, quick, is beneficial to large-scale engineering applications.

Accompanying drawing explanation

[Fig. 1] hardness characterizes electricity schematic diagram; Wherein, 1 is initial electrode material, and 2 occur galvanochemistry dislocation under certain state, and 3 is indentation test;

Composite hardness under [Fig. 2] different SOC and substrate effect;

[Fig. 3] is the composite hardness of lithium ion battery Si negative material.

Embodiment

Below in conjunction with drawings and Examples, the present invention is described in further detail.Following examples are intended to further illustrate content of the present invention, instead of the further restriction to scope.

Embodiment with two-dimensional film electrode material for research object, will verify feasibility and the validity of institute of the present invention method for building up, as shown in Figure 1.

Embodiment 1

Concrete implementation step is as follows:

The first step, by solving diffusion equation, determines the CONCENTRATION DISTRIBUTION of the inner lithium ion of electrode material:

Based on two-dimensional film electrode material, its maximum lithium concentration c ₀be assumed to be constant with diffusion coefficient D, do not change with the change of charge and discharge process, L is the film thickness of t.Thus the lithium concentration of two-dimensional film material is distributed as under can obtaining certain state:

$c=c_0\[1-{\mathrm{\Σ}}_{n=0}^{\mathrm{\∞}}\frac{4{(-1)}^n}{(2n+1)\mathrm{\π}}\exp \[-\frac{{\mathrm{Dt\π}}^2{(2n+1)}^2}{4L^2}\]cos\[\frac{(2n+1)\mathrm{\π}x}{2L}\]\].$

Second step determination t, the electricity of electrode material:

Total electricity of electrode material is the total amount of all electric charges and the ratio of the electricity of electrode material when filled state, so SOC can be expressed as:

Electrochemical bit dislocation density (ρ in 3rd step press-in volume _e):

The electrochemical bit dislocation density ρ ' in certain moment _ecan be obtained by CONCENTRATION DISTRIBUTION, therefore, be h for depth of cup, and press-in volume is the test condition of V, and electrochemical bit dislocation density can be expressed as: ${\mathrm{\ρ}}_e=\frac{{\∫}_0^h{\mathrm{\ρ}}_e^{\′}\·{\mathrm{\πr}}^{2}dh}{V}.$

4th step determination thin-film electrode material hardness H _fand the quantitative resolution relation between SOC:

Consider dislocation theory, statistics is stored dislocation and electrochemical induce dislocation introducing indentation hardness, finally can obtain thin-film electrode material hardness H _fand the quantitative resolution relation between SOC can be expressed as: $\frac{H_F}{H_{F0}}=\sqrt{1+\frac{h_e^{*}}{L_0}\mathrm{\Φ}}.$ Wherein, $h_e^{*}=\frac{27}{4}\frac{M^2{\mathrm{\α}}^{2}b}{\tan \mathrm{\θ}}{\left(\frac{\mathrm{\μ}}{H_0}\right)}^2{\mathrm{\φc}}_0$ For the galvanochemistry factor, (β=h/L be the opposing indentations degree of depth, η be volume expansivity) is electricity controlling elements, the Composite hardness of membrane electrode with the filled state (SOC=1) that charges for reference.

5th step considers the composite hardness under SOC and the acting in conjunction of substrate effect

After considering substrate effect, composite hardness H _ccan be expressed as: wherein, H _sbe substrate hardness, κ is the dimensionless group representing impression response modes, and χ is the dimensionless group representing deformation geometry pattern.The hardness of thin-film electrode material under different state of charge is substituted into this equation, finally obtains the impression composite hardness under consideration SOC and substrate effect double action: as shown in Figure 2.This analytic model not only can obtain the Composite hardness H of electrode material _f0with the hardness H of substrate _s, and can be used for characterizing SOC.

Next, in order to prove feasibility and the validity of embodiment 1, the Si negative material that embodiment 2 have chosen under the different charging and discharging state of lithium ion battery carries out impression test, and the composite hardness obtained and SOC value and theoretical prediction are carried out contrast verification.

Embodiment 2

Concrete implementation step is as follows:

Choosing of first step lithium ion battery Si negative material

Si film [L.A.Berla, S.W.Lee, the Y.CuiandW.D.Nix that thickness is 1.4 μm is prepared by the method for magnetron sputtering, J.PowerSources, 2015,273,41-51], then it is assembled into button cell, is obtained the Si negative material of different electricity by the method for current constant control.

Second step carries out indentation test to the Si negative material under different charging and discharging state

AgilentTechnologiesNanoindenterXP is utilized to carry out indentation test to the negative material obtained, use Berkovich pressure head, depth of cup is less than 1200nm, obtains a series of load-displacement curves, thus the composite hardness of Si negative material under obtaining each state.

The theoretical contrast verification with testing of 3rd step

As shown in Figure 3, along with the increase of SOC, the hardness of Si negative material progressively lowers experimental data, and the softening effect that this galvanochemistry causes is consistent with bibliographical information.Analytic model of the present invention can be good at portraying these experimental datas, result shows, thin-film electrode material Composite hardness is under three circumstances respectively 10GPa (SOC=0), 3.58GPa (SOC=0.51), 1.79GPa (SOC=0.64), simultaneously, no matter how the hardness number of electrode material changes along with electricity, along with the increase of depth of cup, the effect of substrate effect is increasing, final composite hardness is also all tending towards the hardness of Mo substrate, about 3.54GPa, very identical with experimental results.Therefore, utilize theoretical model of the present invention successfully to portray to be in the composite hardness under galvanochemistry and the acting in conjunction of substrate effect, and the Composite hardness of Accurate Prediction electrode material and substrate.

Claims (5)

1. a characterizing method for galvanochemistry and substrate effect acting in conjunction lower electrode material hardness, is characterized in that: comprise the following steps:

(1) utilizing Fick law, consider boundary condition and starting condition, by solving diffusion equation, drawing electrode material diverse location and the distribution of the lithium concentration not in the same time under state;

(2) by the CONCENTRATION DISTRIBUTION of t, integration is carried out to each position, namely obtain electrode material electricity SOC in this condition;

(3) based in charge and discharge process, can there is cubic deformation thus cause a large amount of dislocation in electrode material, be namely defined as electrochemical induce dislocation EID, the average density of electrochemical induce dislocation wherein, ρ ' _efor the electrochemical induce dislocation desity in certain moment distributes, h is depth of cup, and V is press-in volume;

(4), based on dislocation theory, in Indentation Process, total dislocation of hardness is affected wherein, ρ _sfor electrode material statistics itself stores dislocation, have nothing to do with electrochemical process, α, μ and b are respectively material empirical constant, modulus of shearing and Burgers vector;

(5) according to relation σ=M τ, the H=3 σ of mean stress and hardness, wherein, M is Taylor orientation factor, obtains electrode material hardness H _fand the quantitative resolution relation between SOC: $\frac{H_F}{H_{F0}}=\sqrt{1+\frac{h_e^{*}}{L_0}\mathrm{\Φ}};$

Wherein, $h_e^{*}=\frac{27}{4}\frac{M^2{\mathrm{\α}}^{2}b}{\tan \mathrm{\θ}}{\left(\frac{\mathrm{\μ}}{H_0}\right)}^2{\mathrm{\φc}}_0$ For the galvanochemistry factor,

Electricity controlling elements $\mathrm{\Φ}=\[cos\[\frac{\mathrm{\π}\mathrm{\β}}{2}\]+(\frac{\mathrm{\π}\mathrm{\β}}{4}-\frac{2}{\mathrm{\π}\mathrm{\β}})sin\[\frac{\mathrm{\π}\mathrm{\β}}{2}\]\]\frac{(1-SOC)}{(1+\mathrm{\η}SOC){\mathrm{\β}}^2},$

Opposing indentations degree of depth β=h/L, η is volume expansivity,

The Composite hardness of thin-film electrode material with the filled state that charges for reference, i.e. SOC=1;

(6) (5) analytic relationship is introduced substrate effect, by the composite hardness of test electrode material and substrate, namely obtain the hardness of electrode material.

2. the characterizing method of galvanochemistry according to claim 1 and substrate effect acting in conjunction lower electrode material hardness, it is characterized in that: the circular cone pressure head based on two-dimensional film electrode material and semi-cone angle being θ, show that the lithium concentration of two-dimensional film electrode material distributes by step (1):

$c=c_0\[1-{\mathrm{\Σ}}_{n=0}^{\mathrm{\∞}}\frac{4{(-1)}^n}{(2n+1)\mathrm{\π}}\exp \[-\frac{{\mathrm{Dt\π}}^2{(2n+1)}^2}{4L^2}\]cos\[\frac{(2n+1)\mathrm{\π}x}{2L}\]\]$

Wherein,

C ₀for maximum lithium concentration,

D is coefficient of diffusion,

L is the two-dimensional film electrode material thickness of t.

3. the characterizing method of galvanochemistry according to claim 1 and substrate effect acting in conjunction lower electrode material hardness, is characterized in that: in step (2)

4. the characterizing method of galvanochemistry according to claim 1 and substrate effect acting in conjunction lower electrode material hardness, is characterized in that:

Described composite hardness wherein, H _sfor substrate hardness, κ is the dimensionless group of impression response modes, and χ is the dimensionless group of deformation geometry pattern;

The hardness of thin-film electrode material under different state of charge is substituted into composite hardness expression formula,

Obtain $H_C=H_S+\frac{H_{F0}\sqrt{1+\frac{h_e^{*}}{L_0}\mathrm{\Φ}}-H_S}{1+{\mathrm{\κ\β}}^{\mathrm{\χ}}}.$

5. the characterizing method of galvanochemistry according to claim 4 and substrate effect acting in conjunction lower electrode material hardness, is characterized in that: from in can obtain electrode material Composite hardness H _f0with the hardness H of substrate _sand be used for characterizing SOC.