CN103713012A - Method for testing specific heat capacity of lithium ion battery - Google Patents

Abstract

The invention relates to a method for testing specific heat capacity of a lithium ion battery. The method comprises the following steps: measuring and recording open-circuit voltage and surface temperature of the battery in different SOC (State of Charge) states till the SOC of the battery is equal to 0, performing regression analysis on data representing that the open-circuit voltage of the battery changes along with the surface temperature in the different SOC states, so as to obtain a fitting relationship equation of the open-circuit voltage, open-circuit voltage temperature coefficients and different discharge times of the battery, calculating the open-circuit voltage and the open-circuit voltage temperature coefficients at different recorded time points in corresponding discharge by using the relationship equation, calculating heating power of the battery in discharge at each time point, calculating a released thermal value, calculating the SOC states of corresponding moments according to the discharge time and the discharge power so as to obtain the specific heat capacity in the different SOC states. The change of the specific heat capacity of the battery along with the SOC is obtained by using a method with the combination of experimental testing and statistics calculation, and the method is simple and convenient to execute, low in testing cost and wide in application range.

Description

A kind of lithium ion battery specific heat capacity method of testing

Technical field

The invention belongs to lithium ion battery specific heat capacity technical field, be specifically related to a kind of lithium ion battery specific heat capacity method of testing.

Background technology

Lithium example battery, because of the plurality of advantages such as have long service life, environmental sound, specific energy is high, conversion ratio is high, is subject to special favor in the manufacturing enterprises such as electric automobile, Moped Scooter.In the application of power battery pack, lithium battery thermal behavior is the key factor that affects electric battery cycle life and security.

The main accelerating calorimeter that relies on of the specific heat capacity of lithium ion battery test at present, but the size restrictions due to accelerating calorimeter equipment sample pond, specific heat test for large scale battery cannot be carried out, and testing expense is expensive, and cannot obtain in discharge process specific heat capacity with the variation of SOC.

Summary of the invention

The object of the invention is to solve the problems of the technologies described above and a kind of simple and convenient, low testing cost and lithium ion battery specific heat capacity method of testing applied widely implemented is provided.

For achieving the above object, the present invention is by the following technical solutions:

A lithium ion battery specific heat capacity method of testing, comprises the following steps:

The first step: measure and record open-circuit voltage and the surface temperature of battery under different SOC states, until battery SOC=0, the data that the open-circuit voltage of battery under different SOC states is changed with surface temperature are carried out regretional analysis, obtain the open-circuit voltage U of battery _oc, open-circuit voltage temperature coefficient B and different discharge time of t matching relational expression;

U _oc=a ₀+a ₁*t+a ₂*t ²+a ₃*t ³+……+a _f*t ^f （1）

Wherein, a ₀, a ₁, a ₂, a ₃..., a _ffor constant;

B=b ₀+b ₁*t+b ₂*t ²+b ₃*t ³+……+b _kt ^k （2）

Wherein, b ₀, b ₁, b ₂, b ₃..., b _kfor constant;

Second step: battery is discharged and records battery operated voltage U and the surface temperature T variation of t in time, the open-circuit voltage U of each time point of record while utilizing above-mentioned formula (1), (2) to calculate corresponding electric discharge _oc, open-circuit voltage temperature coefficient B;

The 3rd step: the heating power P that calculates the battery discharge of each time point according to following formula:

$P=\frac{1}{V}(U-U_{\mathrm{oc}}+B\·T)$

Wherein, I is electric current, and V is the volume of battery

With n rank polynomial expression, carry out curve fitting, heating power P formula (3) over time while obtaining battery discharge;

P=c ₀+c ₁*t+c ₂*t ²+c ₃*t ³+……+c _n*t ⁿ （3）

C wherein ₀, c ₁, c ₂, c ₃..., c _nfor constant

M time point, i.e. t will be on average divided into the discharge time of battery ₀, t ₁, t ₂..., t _m, then by formula (3) at g discharge time (0≤g≤m) section (t _g-t _g-1) interior integration just can obtain following calorie value formula:

$Q_{g,}=V\&CenterDot;{\&Integral;}_{t_{g-1}}^{t_g}\mathrm{Pdt\; V}\&CenterDot;{\&Integral;}_{t_{g-1}}^{t_g}(c_0+c_1*t{+\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="HDA0000442568990000012.png,HDA0000442568990000022.png"\; state="\{\{state\}\}">c</figure-callout>}}_2*{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA0000442568990000012.png,HDA0000442568990000022.png"\; state="\{\{state\}\}">t</figure-callout>}}^2+{\mathrm{<figure-callout\; id="3"\; label="c"\; filenames="HDA0000442568990000022.png"\; state="\{\{state\}\}">c</figure-callout>}}_3*{\mathrm{<figure-callout\; id="3"\; label="t"\; filenames="HDA0000442568990000022.png"\; state="\{\{state\}\}">t</figure-callout>}}^3+\&CenterDot;\&CenterDot;\&CenterDot;...+c_n*t^n)\mathrm{dt}$

Utilize this calorie value formula to calculate the calorie value that battery discharges in discharge process;

The 4th step: utilize formula below to calculate electric discharge t _gthe specific heat capacity C of moment battery _g

$C_g=\frac{Q_g}{{\mathrm{M\&Delta;T}}_g}=\frac{V{\&Integral;}_{t_{g-2}}^{t_g}\mathrm{Pdt}}{M(T_g-T_{g-1})}$

Wherein, the quality that M is battery;

The SOC state that calculates the corresponding moment according to discharge time and discharge-rate, can obtain the specific heat capacity under different SOC states.

The present invention tests the method combining with statistical computation by experiment, obtains the specific heat capacity of lithium battery with the variation of SOC, and the method is implemented simple and convenient, low testing cost and applied widely.

Accompanying drawing explanation

Figure 1 shows that the test schematic diagram of measuring battery open circuit voltage and surface temperature;

Fig. 2 is the variation schematic diagram of open-circuit voltage with discharge time;

Fig. 3 is the variation schematic diagram of open-circuit voltage temperature coefficient with discharge time;

When Fig. 4 is battery 1C electric discharge, voltage and surface temperature change schematic diagram;

Fig. 5 is hot generating power and the hot generating power matched curve schematic diagram of each time point;

Fig. 6 is the battery specific heat capacity under different SOC states.

Embodiment

Below, in conjunction with example, substantive distinguishing features of the present invention and advantage are further described, but the present invention is not limited to listed embodiment.

The present invention is described in detail as example to take 1C multiplying power discharging below, and other multiplying power discharging method is identical.

The present invention is achieved by following steps:

The first step: measure and record open-circuit voltage and the surface temperature of battery under different SOC states, until battery SOC=0, the data that the open-circuit voltage of battery under different SOC states is changed with surface temperature are carried out regretional analysis, obtain the open-circuit voltage U of battery _oc, open-circuit voltage temperature coefficient B and different discharge time of t matching relational expression;

U _oc=a ₀+ a ₁* t+a ₂* t ²+ a ₃* t ³+ ... + a _f* t ^fformula (1)

Wherein, a ₀, a ₁, a ₂, a ₃..., a _ffor constant;

B=b ₀+ b ₁* t+b ₂* t ²+ b ₃* t ³+ ... + b _kt ^kformula (2)

Wherein, b ₀, b ₁, b ₂, b ₃..., b _kfor constant;

Concrete method of testing is as follows:

As shown in Figure 1, by battery positive and negative electrode connect wire, surface posts thermopair, and be connected with voltage collector, Temperature sampler respectively, battery is full of to electricity and carries out after fully cooling putting into constant temperature oven, according to uniform temperature variation order, as the order of 25 ℃ → 15 ℃ → 5 ℃ → 35 ℃ → 25 ℃, (be enough to guarantee the abundant balanced time of battery temperature) at regular intervals, as a temperature of conversion in 3 hours, and the open-circuit voltage of real time record battery and surface temperature.After temperature variation one-period, at room temperature to be not more than the multiplying power of 1C, emit 10% of battery rated capacity, shelve after a period of time, fully cooling to guarantee battery, after 12 hours, duplicate measurements open-circuit voltage variation with temperature, until the SOC=0 of battery.

1, record the open-circuit voltage U under different SOC states _oc1, U _oc2, U _oc3..., U _oc11and by its to the time (wherein, 1C electric discharge T.T. is 3600s, is divided into 11 time points, therefore, t1=360s, t2=720s ..., t11=3600s)) and make the laggard row f of curve rank polynomial curve fitting, as shown in figure (2), obtain the time dependent schematic diagram of open-circuit voltage, according to this schematic diagram, carry out matching, obtain described fitting formula (1);

2, with the form of U=A*t+B*T, to battery, the temperature-open-circuit voltage curve under different SOC states carries out regretional analysis, and wherein Uoc is open-circuit voltage, the V of unit; T is the time, the s of unit; T is temperature, unit be K or ℃; A, B are constant.Constant B1 in each regretional analysis, B2, B3 ... B11 is the open-circuit voltage temperature coefficient that calculates thermal value.By B1, B2, B3 ... B11 and time are figure, and data are carried out curve fitting with k rank polynomial expression, as shown in Figure 3, obtain temperature coefficient with the variation schematic diagram of discharge time, and according to this schematic diagram, obtain the matching relation formula (2) of the two;

Second step: battery is discharged and records battery operated voltage U and the surface temperature T variation of t in time, and during battery 1C electric discharge, voltage and surface temperature change as shown in Figure 4; The open-circuit voltage U of each time point of record while utilizing above-mentioned formula (1), (2) to calculate corresponding electric discharge _oc, open-circuit voltage temperature coefficient B;

It should be noted that the specific heat capacity while wanting to obtain how many multiplying power discharging just by how many multiplying powers is discharged.

The 3rd step: the heating power P that calculates the battery discharge of each time point according to heating power formula below:

$P=\frac{1}{V}(U-U_{\mathrm{oc}}+B\&CenterDot;T)$

Wherein, P is heating power, the w/m of unit ³; I is electric current, discharges for negative value, and the A of unit; U is battery operated voltage, the V of unit; U _ocopen-circuit voltage, the V of unit; B is the open-circuit voltage temperature coefficient of battery, the V/K of unit; T is battery surface temperature, unit K, and V is battery volume, the m of unit ³.

By the Measurement and Computation of the first step and second step, obtained the open-circuit voltage U of each time point _oc, operating voltage U, open-circuit voltage temperature coefficient B, surface temperature T.Bring above-mentioned numerical value into above-mentioned heating power formula, can obtain the P value of each time point, with n rank polynomial expression, carry out curve fitting, hot generating power formula (3) over time while obtaining battery discharge, heating power P and matched curve are contrasted, as shown in Figure 5

P=c ₀+ c ₁* t+c ₂* t ²+ c ₃* t ³+ ... + c _n* t ⁿformula (3)

Wherein, c ₀, c ₁, c ₂, c ₃..., c _nfor constant

To on average be divided into the quantity of the physical record value of temperature T in m(m=discharge process the discharge time of battery) individual time point, i.e. t ₀, t ₁, t ₂..., t _m, by formula (3) at g discharge time (0≤g≤m) section (t _g-t _g-1) in carry out integration, just can obtain the calorie value Q that battery discharges in discharge process _g:

$Q_{g,}=V\&CenterDot;{\&Integral;}_{t_{g-1}}^{t_g}\mathrm{Pdt}=V\&CenterDot;{\&Integral;}_{t_{g-1}}^{t_g}(c_0+c_1*t{+\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="HDA0000442568990000012.png,HDA0000442568990000022.png"\; state="\{\{state\}\}">c</figure-callout>}}_2*{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA0000442568990000012.png,HDA0000442568990000022.png"\; state="\{\{state\}\}">t</figure-callout>}}^2+{\mathrm{<figure-callout\; id="3"\; label="c"\; filenames="HDA0000442568990000022.png"\; state="\{\{state\}\}">c</figure-callout>}}_3*{\mathrm{<figure-callout\; id="3"\; label="t"\; filenames="HDA0000442568990000022.png"\; state="\{\{state\}\}">t</figure-callout>}}^3+\&CenterDot;\&CenterDot;\&CenterDot;...+c_n*t^n)\mathrm{dt}$

Formula (4)

The 4th step: calculate specific heat capacity C _g

In discharge process, think that the mass M of battery is invariable, so at the specific heat capacity C of g battery in the time period of electric discharge _gcan calculate by formula below:

$C_g=\frac{Q_g}{{\mathrm{M\&Delta;T}}_g}=\frac{V{\&Integral;}_{t_{g-2}}^{t_g}\mathrm{Pdt}}{M(T_g-T_{g-1})}$ Formula (5)

According to above formula, can calculate C ₁, C ₂, C ₃... C _m, according to discharge time and discharge-rate, calculate the SOC state in the corresponding moment, can obtain the specific heat capacity under different SOC states, as shown in Figure 6.

It should be noted that, described polynomial fitting must be able to guarantee that related coefficient is more than 0.99.

Claims (1)

1. a lithium ion battery specific heat capacity method of testing, is characterized in that, comprises the following steps:

The first step: measure and record open-circuit voltage and the surface temperature of battery under different SOC states, until battery SOC=0, the data that the open-circuit voltage of battery under different SOC states is changed with surface temperature are carried out regretional analysis, obtain the open-circuit voltage U of battery _oc, open-circuit voltage temperature coefficient B and different discharge time of t matching relational expression;

U _oc=a ₀+a ₁*t+a ₂*t ²+a ₃*t ³+……+a _f*t ^f （1）

Wherein, a ₀, a ₁, a ₂, a ₃..., a _ffor constant;

B=b ₀+b ₁*t+b ₂*t ²+b ₃*t ³+……+b _kt ^k （2）

Wherein, b ₀, b ₁, b ₂, b ₃..., b _kfor constant;

Second step: battery is discharged and records battery operated voltage U and the surface temperature T variation of t in time, the open-circuit voltage U of each time point of record while utilizing above-mentioned formula (1), (2) to calculate corresponding electric discharge _oc, open-circuit voltage temperature coefficient B;

The 3rd step: the heating power P that calculates the battery discharge of each time point according to following formula:

$P=\frac{1}{V}(U-U_{\mathrm{oc}}+B\&CenterDot;T)$

Wherein, I is electric current, and V is the volume of battery

With n rank polynomial expression, carry out curve fitting, heating power P formula (3) over time while obtaining battery discharge;

P=c ₀+c ₁*t+c ₂*t ²+c ₃*t ³+……+c _n*t ⁿ （3）

C wherein ₀, c ₁, c ₂, c ₃..., c _nfor constant

M time point, i.e. t will be on average divided into the discharge time of battery ₀, t ₁, t ₂..., t _m, then by formula (3) at g discharge time (0≤g≤m) section (t _g-t _g-1) interior integration just can obtain following calorie value formula:

$Q_{g,}=V\&CenterDot;{\&Integral;}_{t_{g-1}}^{t_g}\mathrm{Pdt\; V}\&CenterDot;{\&Integral;}_{t_{g-1}}^{t_g}(c_0+c_1*t{+c}_2*t^2+c_3*t^3+\&CenterDot;\&CenterDot;\&CenterDot;...+c_n*t^n)\mathrm{dt}$

Utilize this calorie value formula to calculate the calorie value that battery discharges in discharge process;

The 4th step: utilize formula below to calculate electric discharge t _gthe specific heat capacity C of moment battery _g

$C_g=\frac{Q_g}{{\mathrm{M\&Delta;T}}_g}=\frac{V{\&Integral;}_{t_{g-2}}^{t_g}\mathrm{Pdt}}{M(T_g-T_{g-1})}$

Wherein, the quality that M is battery;

The SOC state that calculates the corresponding moment according to discharge time and discharge-rate, can obtain the specific heat capacity under different SOC states.

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