CN100483803C - A method for simulating calculating safety performance under high temperature of electrode material for lithium ion cell - Google Patents

Abstract

The invention relates to a method for simulating high-temperature safety property of lithium battery. Wherein, it is characterized in that: (1), first preparing lithium battery pole sample; (2), using one heat measure (as insulated acceleration heat measure) to obtain the temperature increase speed along temperature change of sample; (3) using test to build reaction dynamic model, to build dynamic equation of pole insulated decomposition reaction, using heat measure to test the sample data to obtain the reaction dynamic parameters; (4) using said equation and parameters to calculate out the relation between temperature increase speed and temperature change when discomposing pole material in same electrolyte, any initial temperature and any amount; (5), using Matlab to program and simulate it in computer.

Description

A kind of method of analog computation high temperature of electrode material for lithium ion cell security performance

Technical field

The present invention relates to lithium ion battery electrode material, particularly a kind of anode material for lithium ion battery security performance simulation method belongs to the lithium ion battery field.

Technical background

Advantages such as lithium ion battery has that average output voltage height, specific energy are big, discharging voltage balance and long working life, at present generally as mobile phone, notebook computer, field camera, etc. the power supply of mobile electronic product, in the future also may become the motor vehicle power source, its application is boundless.The lithium ion battery of craving for high power capacity, long circulation life as the battery consumer forever is as its portable type electronic product or electric vehicle power supply.In order to satisfy customer requirement and to increase from the competitive strength in the industry, battery manufacturers is continually developed new battery material and is improved original material and promotes performances such as the capacity of battery and cycle life.For same industrial standard and the rule that requires to satisfy about cell safety of the lithium ion battery of the original material after employing new material or the improvement.For lithium ion battery, wherein one of most important safety problem is exactly battery thermal stability of (such as hot case, acupuncture, extruding and external short circuit etc.) under various abuse conditions.Along with battery capacity is more and more higher, the potential security hidden trouble of battery is more and more outstanding.And the fail safe of lithium ion battery is main relevant with the thermal behavior of battery material, especially be under the above-mentioned various abuse conditions of mentioning, being in the positive electrode active materials and the negative active core-shell material under the embedding lithium state that take off the lithium state is very unsettled [J.Power Sources under the condition that organic electrolyte exists, 2002,108 phases: 8-14 page or leaf].Usually experiment test is the main tool of battery design and performance evaluation, yet experiment will expend a large amount of time and fund, and experiment is difficult to determine that battery is under the high temperature, and the inside battery electrode material carries out the overall process of chemical reaction.

Summary of the invention

The objective of the invention is to overcome the above-mentioned deficiency of prior art, a kind of lithium ion battery electrode material high temperature safe performance computational methods are provided, utilize computational methods provided by the invention, can analog computation have identical electrolyte system, arbitrarily under the initial temperature, the temperature rise rate of the electrode material of arbitrary substance amount varies with temperature relation.Technical scheme of the present invention is as follows:

A kind of method of analog computation lithium ion battery electrode material high temperature safe performance comprises the following steps:

(1) preparation lithium ion battery electrode material sample;

(2) carry out calorimetric experiment obtain comprise temperature that described sample comprises sample thermal decomposition process under adiabatic condition in time with temperature rise rate vary with temperature data at interior sample from adding dsc data;

(3) according to adding dsc data and equation certainly $\ln k=-\frac{E_a}{R}\left(\frac{1}{T}\right)+\ln \mathrm{\γ},$ Try to achieve activation energy (E _a) and pre-exponential factor (γ), and according to $n=\frac{E_a}{{\mathrm{RT}}_{\mathrm{mr}}^2}(T_f-T_{\mathrm{mr}})$ Determine the order of reaction (n);

(4) utilize from adding the parameter that dsc data and step (3) are obtained, according to reaction kinetics equation ${\left[\frac{\mathrm{dT}}{\mathrm{dt}}\right]}_T=\left[\frac{T_f-T}{{\mathrm{\ΔT}}_{\mathrm{ad}}}\right]{x_0}^{n-1}{\mathrm{\ΔT}}_{\mathrm{ad}}\mathrm{\γ}{l}^{\frac{E_a}{\mathrm{RT}}},$ Calculating has under identical electrolyte system, any initial temperature, the temperature rise rate temperature variant relation of electrode material during adiabatic decomposition of arbitrary substance amount, the described lithium ion battery electrode material high temperature safe of quantitative analysis performance.

In technique scheme, the positive electrode of electrode material sample can come from the actual effect lithium ion battery that is charged to 4.2V, is in and takes off the lithium state, and contain electrolyte; The negative material of electrode material sample can come from the actual effect lithium ion battery that is charged to 4.2V, is in embedding lithium state, and contains electrolyte.

Electrode material sample of the present invention from add temperature that dsc data should comprise sample thermal decomposition process under adiabatic condition in time with the data of temperature rise rate with variation of temperature.

The present invention preferably utilizes adiabatic accelerating calorimeter to carry out the calorimetric experiment.When utilizing adiabatic accelerating calorimeter to carry out the calorimetric experiment, preferably adopt heating-wait-seek mode.The calorimetric experiment is done three times at least, determine that by primary calorimetric experiment electrode sample begins to carry out thermal decomposition under adiabatic condition reaction begins temperature and temperature rise rate, when carrying out other each time experiments, directly sample is heated to example reaction and begins initial temperature more than the temperature, each experiment differs than the initial temperature of experiment last time successively and is not less than 5 ℃ and be not more than 10 ℃.

The acquisition methods of kinetic parameter can adopt following method: according to the mapping of the relation between the inverse of the logarithm of reaction rate constant and absolute temperature, obtain straight line, try to achieve activation energy (E according to this straight slope and intercept _a) and pre-exponential factor (γ).

The present invention preferably adopts the Matlab language to programme to realize visual Simulation calculating on computers.

Electrode material for lithium ion cell provided by the invention is the thermal behavior simulation method at high temperature, than the normal experiment research method incomparable advantage is arranged, as be easy to realize, operation easily, speed is fast, cost is low and safety, can help cell designer the battery design initial stage at requirement of client, as high safety performance, select suitable electrode material, and the optimization proportioning of material is instructed.The thermal behavior of the electrode material of this method analog computation and experiment value have anastomose property preferably.Owing to adopt visualization procedure, calculate simple fast, result of calculation provides with the form of chart, simple and clear, reduced by making the actual effect battery and carrying out the loaded down with trivial details operation that battery safety tests the evaluating material thermal stability, have that speed is fast, cost is low, safety, shorten the advantage of material security performance evaluation time greatly, can quicken the research and development of battery, tackle market feedback information fast.Simultaneously also provide parameter and mechanism function for setting up the hot box model of entire cell.

Description of drawings

Fig. 1 is an accelerating calorimeter work basic principle schematic;

Fig. 2 is positive electrode thermal analysis experiment data and curves figure, (a) figure: temperature rise rate-temperature; (b) figure: temperature-time);

Fig. 3 determines kinetic parameter and three thermal analysis experiment data of carrying out;

Fig. 4 handles Fig. 3, and purpose is to be easy to obtain kinetic parameter;

Fig. 5 represents result calculated and experiment value comparison among the embodiment.

Embodiment

Analyze by experiment and set up rational reaction Kinetics Model, on this model based, set up the kinetics equation of electrode reaction, the sample experimental data of utilizing the accelerating calorimeter test to obtain is asked for the reaction power mathematic(al) parameter, and the utilization reaction kinetics equation has under identical electrolyte system, any initial temperature with the kinetic parameter analog computation that experiment obtains, the temperature rise rate of the electrode material of arbitrary substance amount varies with temperature to concern it is very significant.Further specify the present invention below in conjunction with accompanying drawing and representative embodiment (positive electrode), this embodiment not delimit the scope of the invention.

Embodiment

(preparation of electrode sample)

(1) makes lithium ion battery: with cobalt-lithium oxide (LiCoO ₂) as positive electrode active materials, acetylene black is conductive agent, Kynoar (PVDF) is a bonding agent.The proportioning of anode (weight ratio) is: active material (LiCoO ₂): acetylene black: bonding agent=96:2:2.Add a certain amount of N-methyl pyrrolidone (NMP) and mix well into pasty state, be evenly coated on the aluminium foil of 20 micron thickness, roll the cutting oven dry and obtain positive plate.As negative active core-shell material, acetylene black is conductive agent with graphite, and Kynoar (PVDF) is a bonding agent.The proportioning of battery cathode (weight ratio) is: active material: acetylene black: bonding agent=85:5:10.Add a certain amount of N-methyl pyrrolidone (NMP) and mix well into pasty state, be evenly coated on the Copper Foil after 10 microns, roll the cutting oven dry and obtain negative plate.Electrolyte is the organic electrolyte that contains lithium ion, and barrier film is microporous polyethylene or polypropylene film, is assembled into 043048 rectangular cell.In the voltage range of 3.0V～4.2V, on cell tester, carry out charge-discharge test with the speed of 0.2C, after 2-3 circulation, battery is charged to the 4.2V full power state once more.

(2) obtaining of electrode sample: will expire battery (4.2V) and dissect and get utmost point powder 0.5g at the glove box that is full of nitrogen and pack in the preprepared battery case from positive plate, to be measured according to standard cell mounting technology sealed cell shell then, same sample is prepared 3-4 at least, and its purpose and purposes are narrated in the back.

(the heat analysis of electrode sample)

Adopt accelerating calorimeter that the electrode sample that has prepared is carried out heat analysis.The pattern of heating-waits-search (HWS) is adopted in accelerating calorimeter test, determine thermal response (temperature-time) and temperature rise rate (SHR, ℃/min), test by computer and control and carry out according to programming.With thin copper wire sample is suspended on calorimeter center heating place, set test parameter, sample at first is heated to predefined temperature from room temperature, next a wait process is arranged, its objective is and allow calorimeter, the whole system of sample and shuttle reaches heat balance, after waiting for end, instrument begins to search the temperature rate-of-rise of sample and the whole system of shuttle, if temperature rate-of-rise less than default sensitivity (0.02 ℃/min), system will enter heating mode automatically so, heat up again one and heat step-length (5 ℃ or 10 ℃), this heating-wait-seek mode can continue always circulation go down up to detect exothermic reaction (heating rate greater than 0.02 ℃/min) or arrive final temperature.When detecting exothermic reaction, Jia Re sample temperature is with tracked certainly, and instrumentation control system remains sample temperature and the calorimeter temperature is synchronous, guarantees to test under adiabatic condition and carries out.Fig. 1 is an accelerating calorimeter work basic principle schematic.Carry out this experiment two purposes are arranged: the one, research electrode material pyrolysis dynamics, estimation electrode Thermal Decomposition Kinetic Parameters; The 2nd, checking electrode material Thermal Decomposition Mechanism model (functional relation) correctness.We are based on such consideration when estimation electrode Thermal Decomposition Kinetic Parameters: according to famous A Luoniwusi empirical formula experimental data is handled and preresearch estimates reaction activity and pre-exponential factor.Reach such purpose, need carry out following thermal analysis experiment: at first electrode sample is done and tentatively groped experiment, 50-250 ℃ of experimental temperature scope, the instrument test result shows that electrode sample adds thermal response certainly 150 ℃ of beginnings, first exothermic reaction finishes near 190 ℃ greatly, as shown in Figure 2.The experiment of carrying out subsequently as shown in Figure 3, temperature range is respectively 165-250 ℃; 170-250 ℃.Logarithmic form according to atmospheric equation: $\ln k=-\frac{E_a}{R}\left(\frac{1}{T}\right)+\ln \mathrm{\γ}$ Fig. 3 is handled, make lnk～1/T curve (Fig. 4), can try to achieve reaction activity E according to the slope and the intercept of straight line _aWith pre-exponential factor γ.

(foundation of electrode sample reaction Kinetics Model)

Because the sample thermal analysis experiment carries out, therefore there is following relational expression under adiabatic condition:

$\frac{\mathrm{dp}}{\mathrm{dt}}\≡\frac{\mathrm{dT}}{\mathrm{dt}}\≡-\frac{\mathrm{dx}}{\mathrm{dt}}={\mathrm{\γe}}^{\frac{E_a}{\mathrm{RT}}}{x}^n---\left(1\right)$

From the thermodynamics angle analysis, under the adiabatic condition, there is following relation in the reactant concentration when reactant initial concentration and random time t with temperature:

x∝T _f-T (2)

x ₀∝T _f-T ₀＝ΔT _ad (3)

So, exist

$x=\frac{T_f-T}{{\mathrm{\ΔT}}_{\mathrm{ad}}}{x}_0---\left(4\right)$

Equation (4) both sides to time t differential, are got

$\frac{\mathrm{dx}}{\mathrm{dt}}=-\frac{x_0}{{\mathrm{\ΔT}}_{\mathrm{ad}}}\frac{\mathrm{dT}}{\mathrm{dt}}---\left(5\right)$

According to basic motive rate equation (6) and A Luoniwusi empirical formula (7), can obtain functional relation (8) again

$-\frac{\mathrm{dx}}{\mathrm{dt}}={\mathrm{kx}}^n---\left(6\right)$

$k={\mathrm{\γe}}^{-\frac{E_a}{\mathrm{RT}}}---\left(7\right)$

$\frac{\mathrm{dT}}{\mathrm{dt}}=\frac{{\mathrm{\ΔT}}_{\mathrm{ad}}}{x_0}{\mathrm{\γe}}^{-\frac{E_a}{\mathrm{RT}}}{x}^n---\left(8\right)$

Equation (4) substitution equation (8) can be got functional relation (9)

${\left(\frac{\mathrm{dT}}{\mathrm{dt}}\right)}_T={\left(\frac{T_f-T}{{\mathrm{\ΔT}}_{\mathrm{ad}}}\right)}^n{{x_0}^{n-1}{\mathrm{\ΔT}}_{\mathrm{ad}}\mathrm{\γe}}^{-\frac{E_a}{\mathrm{RT}}}---\left(9\right)$

The implication of parameter sees Table 1 in equation (1)-(9).

Table 1 parameter Verbose Listing

The parameter code

Title and physical meaning

Unit

P	Pressure	N/m 2
			t	Time	min
T	Temperature	K
			x	Any time reactant concentration	mol/L
x 0	The reactant initial concentration	mol/L
			γ	Pre-exponential factor	Min -1
E a	Activation energy	kJ/mol
			n	The order of reaction	-
T f	The reaction terminating temperature	K
			T 0	Reaction beginning temperature	K
T ad	The adiabatic temperature rise of sample	K
			T mr	Temperature during maximum rate	K
k	Reaction rate constant	s -1·L·mol -1

(analog computation)

Adopt the executable computer program of Matlab language compilation to carry out analog computation on computers.In order to verify the accuracy of analog result, the data that will test collection simultaneously also adopt the Matlab language compilation to become computer executable program, call experimental data and map the two is compared after obtaining result of calculation, as shown in Figure 5.Result calculated and experiment value have good consistency in first main exothermic reaction as can be seen from Figure 5.Fig. 2 is that experimental data figure is decomposed in the thermal insulation of positive electrode (cobalt-lithium oxide), at 150-250 ℃ of this material three exothermic reactions are arranged as can be seen from Figure 2, but first exothermic heat of reaction amount maximum plays a leading role.Therefore, for simplified model, first reaction is selected in analog computation, make such choice also based on following 2 considerations: (1) analyze experimental result in conjunction with the accelerating calorimeter to entire cell and the complete pole piece of both positive and negative polarity thereof before us, experiment finds with the cobalt-lithium oxide to be that the lithium ion battery of electrode active material begins thermal runaway near 165 ℃, and to cause the immediate cause of battery thermal runaway be the cobalt-lithium oxide material thermal decomposition.Therefore, heat and the gas of investigating the exothermic reaction generation of cobalt-lithium oxide material after 200 ℃ have little significance to causing entire cell thermal runaway reason to be explored, because battery explodes out of control already under this temperature; (2) if in also considering the exothermic reaction of back again, need estimate reaction power mathematic(al) parameter separately equally in computational process, and the dynamic experiment that carries out latter two reaction is very difficult to obtain kinetic parameter.

In the analog computation process, we have carried out following two aspect work: utilize estimated parameters and kinetics equation to carry out analog computation on the one hand, carry out every analog computation by revising parameter on the other hand, make result of calculation as much as possible near actual value (experiment value), play again so conversely and optimized parameter, the purpose of the adiabatic decomposition kinetics equation of perfect electrode is more accurate to the high temperature of electrode material safety prediction.

Claims (9)

1. the method for an analog computation lithium ion battery electrode material high temperature safe performance comprises the following steps:

(1) preparation lithium ion battery electrode material sample;

(2) carry out calorimetric experiment obtain comprise temperature that described sample comprises sample thermal decomposition process under adiabatic condition in time with temperature rise rate vary with temperature data at interior sample from adding dsc data;

(3) according to adding dsc data and equation certainly $\ln k=-\frac{E_a}{R}\left(\frac{1}{T}\right)+\ln \mathrm{\γ},$ Try to achieve activation energy (E _a) and pre-exponential factor (γ), and according to $n=\frac{E_a}{{\mathrm{RT}}_{\mathrm{mr}}^2}(T_f-T_{\mathrm{mr}})$ Determine the order of reaction (n);

(4) utilize from adding the parameter that dsc data and step (3) are obtained, according to reaction kinetics equation ${\left[\frac{\mathrm{dT}}{\mathrm{dt}}\right]}_T=\left[\frac{T_f-T}{{\mathrm{\ΔT}}_{\mathrm{ad}}}\right]{x_0}^{n-1}{\mathrm{\ΔT}}_{\mathrm{ad}}{\mathrm{\γl}}^{-\frac{E_a}{\mathrm{RT}}},$ Calculating has under identical electrolyte system, any initial temperature, the temperature rise rate temperature variant relation of electrode material during adiabatic decomposition of arbitrary substance amount, the described lithium ion battery electrode material high temperature safe of quantitative analysis performance.

2. the method for analog computation lithium ion battery electrode material high temperature safe performance according to claim 1, it is characterized in that the positive electrode of described electrode material sample comes from the actual effect lithium ion battery that is charged to 4.2V, be in and take off the lithium state, and contain electrolyte.

3. the method for analog computation lithium ion battery electrode material high temperature safe performance according to claim 1, it is characterized in that, the negative material of this electrode material sample comes from the actual effect lithium ion battery that is charged to 4.2V, is in embedding lithium state, and contains electrolyte.

4. the method for analog computation lithium ion battery electrode material high temperature safe performance according to claim 1, it is characterized in that, described electrode material sample heat certainly temperature that data comprise sample thermal decomposition process under adiabatic condition in time with the data of temperature rise rate with variation of temperature.

5. the method for analog computation lithium ion battery electrode material high temperature safe performance according to claim 1 is characterized in that, utilizes adiabatic accelerating calorimeter to carry out the calorimetric experiment.

6. the method for calculating lithium ion battery electrode material high temperature safe performance according to claim 5 is characterized in that, adopts heating-wait-seek mode when utilizing described adiabatic accelerating calorimeter to carry out the calorimetric experiment.

7. the method for analog computation lithium ion battery electrode material high temperature safe performance according to claim 1, it is characterized in that, calorimetric experiment in the step (2) is done three times at least, determine that by primary calorimetric experiment electrode sample begins to carry out thermal decomposition under adiabatic condition reaction begins temperature and temperature rise rate, when carrying out other each time experiments, directly sample is heated to example reaction and begins initial temperature more than the temperature, each experiment differs than the initial temperature of experiment last time successively and is not less than 5 ℃ and be not more than 10 ℃.

8. the method for analog computation lithium ion battery electrode material high temperature safe performance according to claim 1, it is characterized in that, in step (3), according to the mapping of the relation between the inverse of the logarithm of reaction rate constant and absolute temperature, obtain straight line, try to achieve activation energy (E according to this straight slope and intercept _a) and pre-exponential factor (γ).

9. the method for analog computation lithium ion battery electrode material high temperature safe performance according to claim 1 is characterized in that, adopts the Matlab language to programme to realize visual Simulation calculating on computers.

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