CN102116846A - Method for measuring energy efficiencies of storage batteries - Google Patents

Abstract

The invention discloses a method for measuring the energy efficiency of a storage battery, which comprises the steps of: calculating the static energy of the battery pack in any charge state interval according to the quantitative relational expression of the open circuit voltage of the battery pack and the state of charge; Constant current charging to the charge cut-off voltage, record the curve of the average charging voltage of the battery pack monomer and the change of the state of charge, and obtain the electric energy charged into the battery pack in any state of charge interval according to the curve; the battery pack at the discharge cut-off voltage Rush to the charge cut-off voltage with a constant current of 0.33C, and then discharge to the discharge cut-off voltage with a constant current, record the curve of the average discharge voltage of the battery pack monomer and the state of charge change, and obtain the battery pack in any state of charge interval according to the curve. Discharged electric energy; calculate battery energy efficiency based on battery net energy, charged electric energy or discharged electric energy in the same state of charge range. The method can measure the energy efficiency of the battery, the measuring method is simple and the measuring result is stable.

Description

Storage battery energy efficiency measurement method

Technical field

The present invention relates to the electrochmical power source applied technical field, particularly a kind of measurement accumulator, the especially method of power storage battery energy efficient.

Background technology

Battery is the device that the chemical energy of storing in the active material is directly changed into electric energy by electrochemical redox reaction.Secondary cell, i.e. accumulator, the reverse charging by discharge process is recovered the active material chemical energy that has discharged, can reuse.Convert chemical energy to electric energy during battery discharging, convert electric energy to chemical energy during charging, these two processes are different with internal combustion engine or hot machine, can avoid the restriction by Carnot cycle in the second law of thermodynamics, thereby battery have high energy conversion efficiency.Battery can provide electric power and easy to carry for various device, and is widely used in multiple field.

Be different from small battery, big-and-middle-sized accumulator, the power accumulator that particularly is applied to electric automobile in use, except the fundamental characteristics of paying close attention to battery such as capacity, specific energy, specific power etc., also need research and the closely-related performance of automobile-used environment such as temperature, power, energy efficiency characteristic etc.Wherein, the energy efficiency of measuring power accumulator has significant meaning: 1) optimize battery operated parameter and improve energy conversion efficiency, to economize on resources; 2) known discharge energy efficient can be judged the discharge concluding time, the continuous mileage of speeding of measurable automobile for pure electric automobile; 3) energy efficiency of the performance of battery and battery complements each other, and can distinguish the battery performance quality by the comparison of energy efficiency; 4) energy is a conservation, and the electric energy of loss or chemical energy mainly are transformed into heat energy, measures energy efficiency and can analyze the battery generation of heat at work, is convenient to the heat management of battery.

Therefore, be necessary to provide a kind of storage battery energy efficiency measurement method.

Summary of the invention

The energy efficiency measuring method that the purpose of this invention is to provide accumulator, the energy efficiency of energy measurement accumulator.

To achieve these goals, the invention provides a kind of storage battery energy efficiency measurement method, comprise the steps:

(1) calculate the rest energy of the electric battery in arbitrary state-of-charge interval according to the quantitative relation formula of open-circuit voltage and state-of-charge, computing formula is:

Wherein, Δ Q _nBe rest energy, C _nBe rated capacity, SOC (0) to SOC (t) be the state-of-charge interval;

(2) will stop to the cut-off voltage that charges with constant-current charge according to the discharge system exhausted cell group that battery types is determined, the curve that the charging average voltage of record batteries monomer changes with state-of-charge is defined as the electric energy that electric battery charges in this electric current and state-of-charge interval with this curve the amassing of the integral result in arbitrary state-of-charge interval and rated capacity;

(3) will be full of electric electric battery according to the charging system that battery types is determined stops to discharge cut-off voltage with constant-current discharge, the curve that the discharge average voltage of record batteries monomer changes with state-of-charge is defined as the electric energy that electric battery is emitted in this electric current and state-of-charge interval with this curve the amassing of the integral result in arbitrary state-of-charge interval and described rated capacity;

(4) determine the state-of-charge interval, the rest energy of electric battery in this state-of-charge interval and the merchant of the electric energy that charges in this state-of-charge interval are defined as the rechargeable energy efficient of electric battery, the electric energy that electric battery is emitted in this state-of-charge interval and the merchant in the rest energy in this state-of-charge interval are defined as the discharge energy efficient of electric battery, and the electric energy that electric battery is emitted in this electric current and state-of-charge interval and the merchant of the electric energy that charges in this electric current and state-of-charge interval are defined as the charge-discharge energy efficient of electric battery.

In one embodiment of the invention, the process of setting up of the quantitative relation formula of electric battery open-circuit voltage and state-of-charge is in the described step (1):

(11) electric battery that will be in discharge cut-off voltage stops the charging curve that record batteries monomer charging voltage changes with state-of-charge with 0.04C constant-current charge 25h or to the cut-off voltage that charges;

(12) with described electric battery with 0.04C constant-current discharge 25h after or behind voltage, stop the discharge curve that record batteries monomer sparking voltage changes with state-of-charge to discharge;

(13) described charging curve and described discharge curve addition are averaged, obtain the open-circuit voltage curve that the batteries monomer open-circuit voltage changes with state-of-charge;

(14) according to the relational expression U of open-circuit voltage with state-of-charge _Ocv=E ₀+ K ₁LnSOC+K ₂The respective value of ln (1-SOC) and described open-circuit voltage curve is obtained the unknown parameter in the relational expression, and then obtains the quantitative relation formula of open-circuit voltage and state-of-charge, wherein U _OcvBe open-circuit voltage, SOC is a state-of-charge, E ₀, K ₁, K ₂Be unknown parameter

In another embodiment of the present invention, described method also comprises:

Behind charging or the discharge off, with static a period of time of described electric battery.

In an embodiment more of the present invention, described step (2) is identical with battery pack temperature in the step (3).

In another embodiment of the present invention, described method also comprises:

Determine charging system and discharge system according to battery types;

Electric battery is intact with its residue tele-release according to the discharge system of determining, then charge to charging by voltage according to the charging system of determining, be discharged to discharge by voltage according to the discharge system of determining then, the charge value of being emitted be defined as the rated capacity of electric battery.

In an embodiment more of the present invention, described step (4) also comprises:

To stop to the cut-off voltage that charges with a plurality of different constant-current charges according to the discharge system exhausted cell group of determining, obtain the electric energy that corresponding each constant current of electric battery charges in arbitrary state-of-charge interval;

Then, described step (4) also comprises:

Determine the state-of-charge interval, obtain the rechargeable energy efficient of corresponding each constant current of electric battery;

The rechargeable energy efficient of corresponding all constant currents of electric battery by linear match or fitting of a polynomial, is obtained the experimental formula of rechargeable energy efficient and electric current: η _Charge=0.99121-0.04221 * I+0.0082 * I ², wherein, η _ChargeBe rechargeable energy efficient, I is an electric current.

In another embodiment of the present invention, described step (4) also comprises:

To be full of electric electric battery according to the charging system of determining and to discharge cut-off voltage, stop with a plurality of different constant-current discharges,, obtain the electric energy that corresponding each constant current of electric battery is emitted in arbitrary state-of-charge interval;

Determine the state-of-charge interval, obtain the discharge energy efficient of corresponding each constant current of electric battery;

The discharge energy efficient of corresponding all constant currents of electric battery by linear match or fitting of a polynomial, is obtained the experimental formula of discharge energy efficient and electric current: η _Disch=0.99722-0.04137 * I+0.00344 * I ², wherein, η _DischBe discharge energy efficient, I is an electric current.

Compared with prior art, the energy efficiency of storage battery energy efficiency measurement method energy measurement accumulator of the present invention, and test process is simple, and measurement result is stable, and is applied widely.

By following description also in conjunction with the accompanying drawings, it is more clear that the present invention will become, and these accompanying drawings are used to explain embodiments of the invention.

Description of drawings

Fig. 1 is the process flow diagram of storage battery energy efficiency measurement method of the present invention.

The sparking voltage when charging voltage when Fig. 2 has showed the 0.04C constant-current charge and the charging curve of SOC relation, 0.04C constant-current discharge and charging curve, the open-circuit voltage curve of SOC relation, fit the open-circuit voltage curve.

Charging average voltage when Fig. 3 has showed the 2C constant-current charge and the charging curve of SOC relation and fit the open-circuit voltage curve.

Discharge average voltage when Fig. 4 has showed the 2C constant-current discharge and the discharge curve of SOC relation and fit the open-circuit voltage curve.

Embodiment

With reference now to accompanying drawing, describe embodiments of the invention, the similar elements label is represented similar elements in the accompanying drawing.

Before explanation storage battery energy efficiency measurement method of the present invention, earlier the several notions that relate to are described.

The rechargeable energy efficient of battery: finish when battery being charged to charging, the energy of charge power supply input battery is designated as Q _In, the energy variation of battery own is designated as Δ Q _n, then the expression formula of the energy efficiency in the battery charging process is:

η _charge＝ΔQ _n/Q _in (1)

The discharge energy efficient of battery: finish when battery begins to be discharged to discharge, the energy that battery is defeated by discharge load is designated as Q _Out, the energy variation of battery own is designated as Δ Q _n, then the expression formula of the discharge energy efficient of battery is:

η _disch＝Q _out/ΔQ _n (2)

The charge-discharge energy efficient of battery: under certain conditions (temperature, rate of charge etc.) to certain state-of-charge (SOC), the energy of charge power supply input battery is designated as Q with battery charge _In, (temperature, discharge-rate etc.) discharge battery under same condition then, and the energy that battery is defeated by discharge load is designated as Q _Out, then the charge and discharge process energy efficiency of battery under this condition is:

η _battery＝Q _out/Q _in (3)

Below storage battery energy efficiency measurement method of the present invention is elaborated.The LiFePO that following embodiment produces for certain company with electric battery ₄The type lithium-ion-power cell is an example, and its rated capacity is 60Ah, and electric battery is by 30 monomer series-connected compositions.

Below with reference to Fig. 1 and in conjunction with Fig. 2,3 and Fig. 4, storage battery energy efficiency measurement method of the present invention is described.Described method comprises the steps:

Step S1 determines charging system and discharge system according to battery types, and battery types is LiFePO in the present embodiment ₄Battery (determines that charging system and discharge system are the prerequisites to the battery implementation and operation, can determine how battery is full of according to these systems, how that the battery tele-release is intact, measure rated capacity and residual capacity, determine that charging is by voltage or termination condition, discharge is by voltage or termination condition, in charging system and discharge system, comprised rest time, all want static a period of time just can carry out next step operation whenever finishing a charge or discharge process electric battery, in generation any change be not as the criterion with cell voltage rest time, usually need 2h at this example, charging system and discharge system both can be provided by battery production producer, also can be according to national standard such as QC/T742-2006, QC/T743-2006 and QC/T744-2006 be corresponding lead-acid battery respectively, Ni-MH battery and lithium ion battery are set);

Step S2 determines LiFePO ₄The rated capacity of electric battery: with LiFePO ₄Electric battery is intact with its residue tele-release according to the discharge system (with the 0.33C constant-current discharge) that step S1 determines, then the charging system of determining according to step S1 (with the 0.33C constant-current charge) charges to charging by voltage, the monomer average voltage reaches 3.6V, the ceiling voltage that battery can reach under the normal condition), (the monomer average voltage is to 2.5V by voltage to be discharged to discharge according to the definite discharge system (with the 0.33C constant-current discharge) of step S1 then, the minimum voltage that battery can reach under the normal condition), the charge value that record is emitted is LiFePO ₄The rated capacity of electric battery, in the present embodiment, measured value is 60Ah, promptly rated capacity is 60Ah;

Step S3 is with LiFePO ₄Electric battery is with 0.33C (charging and discharge current value that QC/T744-2006 adopts when the test rated capacity is provided, needing that in this example battery is full of electricity or having put the size of current that electricity uses is exactly 0.33C) constant-current discharge is to discharge cut-off voltage, behind the static 2h, or to the cut-off voltage that charges, stop record LiFePO with 0.04C constant-current charge 25h (time that is full of electricity of 0.04C correspondence is exactly 25h) ₄The charging curve that the batteries monomer charging voltage changes with state-of-charge (SOC) is shown in label among Fig. 21;

Step S4, static 2h, the LiFePO that step S3 is obtained ₄Electric battery stops record LiFePO with 0.04C constant-current discharge 25h (time that has put electricity of 0.04C correspondence is exactly 25h) back or to discharging behind voltage ₄The discharge curve that the batteries monomer sparking voltage changes with state-of-charge (SOC) is shown in label among Fig. 24;

Step S5, the discharge curve addition that charging curve that step S3 is obtained and step S4 obtain is averaged, and obtains LiFePO ₄Batteries monomer open-circuit voltage (U _OCV) the open-circuit voltage curve that changes with state-of-charge (SOC), shown in label among Fig. 22 (why choose way that the discharge curve addition of the charging curve of 0.04C and 0.04C averages obtain the open-circuit voltage curve be) according to document (J Power Sources, 134 (2004) 262-272);

Step S6, the open-circuit voltage (U that provides according to document (J Power Sources, 134 (2004) 262-272) _OCV) with the relational expression U of SOC _Ocv=E ₀+ K ₁LnSOC+K ₂Ln (1-SOC), battery open circuit voltage U in the open-circuit voltage curve that step S5 is obtained _OCVWith the respective value substitution above-mentioned relation formula of state-of-charge (SOC), take iterative manner to obtain three unknown parameter E in the above-mentioned relation formula ₀, K ₁, K ₂Thereby, set up battery open circuit voltage U _OCVWith the quantitative relation formula of state-of-charge SOC, obtain fitting curve according to this quantitative relation formula, shown in label among Fig. 23 (in Fig. 1, open-circuit voltage curve 2 coincide with matched curve in 30 minutes, showed that the precision of match is higher);

Step S7 determines state-of-charge (SOC) interval (be SOC (0) to SOC (t), wherein, SOC (0) be initial SOC, SOC (t) is for stopping SOC), calculates the rest energy of the electric battery in described state-of-charge (SOC) interval, and computing formula is:

${\mathrm{\ΔQ}}_n={\∫}_{\mathrm{SOC}\left(0\right)}^{\mathrm{SOC}\left(t\right)}{U}_{\mathrm{COV}}{C}_n\mathrm{dSOC}---\left(4\right)$

Wherein, Δ Q _nBe the rest energy of electric battery, C _nThe LiFePO that obtains for step S2 ₄The rated capacity of electric battery is with battery open circuit voltage U among the step S6 _OCVQuantitative relation formula substitution equation (4) with state-of-charge SOC obtains:

${\mathrm{\&Delta;Q}}_n={\&Integral;}_{\mathrm{SOC}\left(0\right)}^{\mathrm{SOC}\left(t\right)}({\mathrm{<figure-callout\; id="0"\; label="E"\; filenames="HDA0000042714930000021.png,HDA0000042714930000022.png"\; state="\{\{state\}\}">E</figure-callout>}}_0+K_1\ln \mathrm{SOC}+{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="HDA0000042714930000021.png"\; state="\{\{state\}\}">K</figure-callout>}}_2\ln (1-\mathrm{SOC}))C_n\mathrm{dSOC}---\left(5\right)$

In equation (5), C _n, E ₀, K ₁, K ₂Known, determine state-of-charge (SOC) interval after, can obtain corresponding rest energy Δ Q _n, determine as long as state-of-charge is interval, just can calculate the rest energy of electric battery correspondence;

Step S8 is under 20 ± 5 ℃ of conditions, with charged LiFePO ₄Electric battery is with 0.33C (charging and discharge current value that QC/T744-2006 adopts when the test rated capacity is provided, needing in this example battery is full of electricity or has put the electric size of current of using is exactly 0.33C) constant-current discharge, stop discharge during to discharge cut-off voltage, static 2h, then under the uniform temp condition, to the cut-off voltage that charges, stop record LiFePO with the 2C constant-current charge ₄The average voltage U of the charging of batteries monomer _ChargeThe average voltage curve of charging (charging curve under the 2C multiplying power) that same state-of-charge (SOC) changes, shown in label among Fig. 35, then the electric energy that charges into of the interval electric battery of state-of-charge (SOC) is:

$Q_{\mathrm{in}}={\&Integral;}_{\mathrm{SOC}\left(0\right)}^{\mathrm{SOC}\left(t\right)}{U}_{\mathrm{ch}\arg e}{C}_n\mathrm{dSOC}---\left(5\right)$

Wherein, Q _InBe the electric energy that charges into, C _nThe LiFePO that obtains for step S1 ₄The rated capacity of electric battery, the scope of state-of-charge (SOC) interval [SOC (0), SOC (t)] are 0 to label 6 pairing abscissa value.The calculating formula of SOC (t) is: SOC (t)=SOC (0)-I * t/C _n, I is electric current (be negative value during charging, be on the occasion of) during discharge, t is the duration of charging, in fact, calculates Q _InOnly need the curvilinear integral of Fig. 3 label 5 be multiply by C again _n, determine as long as state-of-charge is interval, just can calculate the electric energy that the electric battery correspondence charges into;

Step S9 is under 20 ± 5 ℃ of conditions, with charged LiFePO ₄Electric battery is with 0.33C constant current (charging and discharge current value that QC/T744-2006 adopts when the test rated capacity is provided, needing in this example battery is full of electricity or has put the electric size of current of using is exactly 0.33C) discharge, stop discharge during to discharge cut-off voltage, leave standstill 2h, then under the uniform temp condition, with 0.33C (charging and discharge current value that QC/T744-2006 adopts when the test rated capacity is provided, needing that in this example battery is full of electricity or having put the size of current that electricity uses is exactly 0.33C) constant current dashes and stops when charging cut-off voltage, stop record LiFePO again during to discharge cut-off voltage with the 2C constant-current discharge ₄Discharge average voltage (the U of batteries monomer _Disch) the discharge average voltage curve (discharge curve under the 2C multiplying power) that changes of same state-of-charge (SOC), shown in label among Fig. 47, then the interval electric battery of state-of-charge (SOC) electric energy of emitting is:

$Q_{\mathrm{out}}={\&Integral;}_{\mathrm{SOC}\left(0\right)}^{\mathrm{SOC}\left(t\right)}{U}_{\mathrm{disch}}{C}_n\mathrm{dSOC}---\left(6\right)$

Wherein, Q _OutBe the electric energy of emitting, the scope of state-of-charge (SOC) interval [SOC (0), SOC (t)] is 1 to label 8 pairing abscissa value, in fact, calculates Q _OutOnly need the curvilinear integral of Fig. 4 label 7 be multiply by C again _n, determine as long as state-of-charge is interval, just can calculate the electric energy that the electric battery correspondence is emitted;

Step S10, the electric energy Q that charges into that obtains according to step S8 when identical state-of-charge (SOC) is interval _InThe rest energy Δ Q that obtains with step S7 _nRechargeable energy efficiency eta in the counting cell charging process _Charge, computing formula is η _Charge=Δ Q _n/ Q _In(among Fig. 3, Δ Q _nCorresponding matched curve 3 is positioned at Q _InUnder the corresponding average voltage curve 5 of charging (size of current 2C), promptly at identical SOC interval, Δ Q _nLess than Q _In), if in step S8 conversion charging current size (promptly do not adopt the 2C constant-current charge, adopt other constant-current charges), can obtain the rechargeable energy efficiency eta under the different current conditions _Charge, can obtain the rechargeable energy efficiency eta by linear match or fitting of a polynomial _ChargeExperimental formula with electric current I: η _Charge=0.99121-0.04221 * I+0.0082 * I ², wherein the unit of I is multiplying power C;

Step S11, the electric energy Q that emits that obtains according to step S9 when identical state-of-charge (SOC) is interval _OutThe rest energy Δ Q that obtains with step S7 _nDischarge energy efficiency eta in the counting cell discharge process _Disch, computing formula is η _Disch=Q _Out/ Δ Q _n(among Fig. 4, Δ Q _nCorresponding matched curve 3 is positioned at Q _OutOn the corresponding discharge average voltage curve 7 (size of current is 2C), promptly at identical SOC interval, Δ Q _nGreater than Q _Out), if in step S9 conversion discharge current size (promptly do not adopt the 2C constant-current discharge, adopt other constant-current discharges), can obtain the discharge energy efficiency eta under the different current conditions _DischValue can obtain the discharge energy efficiency eta by linear match or fitting of a polynomial _DischExperimental formula with electric current I: η _Disch=0.99722-0.04137 * I+0.00344 * I2, wherein the unit of I is multiplying power C;

Step S12 is according to the electric energy Q that charges into interval at identical state-of-charge (SOC) and that step S8 obtains when adopting identical constant current charge-discharge _InThe electric energy Q that emits that obtains with step S9 _OutThe charge-discharge energy efficiency eta of counting cell _Battery, computing formula is η _Battery=Q _Out/ Q _In, during calculating, step S8 charging current and step S9 discharge current size are identical, and for example charging current is 2C among the step S8, and then discharge current also is 2C among the step S9.

Need to prove, among above-mentioned steps S8 and the step S9, also can adopt constant-current charge, discharge except that the 2C constant current, can realize the storage battery energy measurement, measuring process and said method are similar.

Above invention has been described in conjunction with most preferred embodiment, but the present invention is not limited to the embodiment of above announcement, and should contain various modification, equivalent combinations of carrying out according to essence of the present invention.

Claims (7)

1. A method for measuring battery energy efficiency, comprising the steps of: (1) Calculate the static energy of the battery pack in any state of charge interval by using the quantitative relationship between the open circuit voltage of the battery pack and the state of charge. The calculation formula is:

Among them, ΔQ _n is the static energy, C _n is the rated capacity, and SOC(0) to SOC(t) is the state of charge interval; (2) Charge the battery pack that has been fully discharged according to the discharge system determined by the battery type at a constant current to the charging cut-off voltage, then stop, record the curve of the average charging voltage of the battery pack monomer and the change of the state of charge, and use the curve at any The product of the integration result of the state of charge interval and the rated capacity is determined as the electric energy charged by the battery pack in the current and state of charge interval; (3) Discharge the fully charged battery pack according to the charging system determined by the battery type at a constant current to the discharge cut-off voltage and then stop, record the curve of the average discharge voltage of the battery pack monomer and the change of the state of charge, and use the curve at any charge The product of the integration result of the state of charge range and the rated capacity is determined as the electric energy released by the battery pack in the current and state of charge range; (4) Determine the state of charge interval, determine the quotient of the static energy of the battery pack in the state of charge interval and the electric energy charged in the state of charge interval as the charging energy efficiency of the battery pack, and determine the charging energy efficiency of the battery pack in the state of charge interval. The quotient of the electric energy released in the state of charge interval and the static energy in the state of charge interval is determined as the discharge energy efficiency of the battery pack. The quotient of the charged electric energy is determined as the charge and discharge energy efficiency of the battery pack. 2. storage battery energy efficiency measuring method as claimed in claim 1, is characterized in that, in described step (1), the process of establishing the quantitative relational expression of battery pack open circuit voltage and state of charge is: (11) Charge the battery pack at the discharge cut-off voltage with a constant current of 0.04C for 25 hours or stop after reaching the charge cut-off voltage, and record the charging curve of the battery pack monomer charging voltage changing with the state of charge; (12) Discharging the battery pack at a constant current of 0.04C for 25h or stopping after the discharge cut-off voltage, and recording the discharge curve of the battery pack monomer discharge voltage changing with the state of charge; (13) adding the charging curve and the discharging curve to get an average value to obtain the open circuit voltage curve of the open circuit voltage of the battery pack monomer as the state of charge changes; (14) According to the relational expression U _ocv =E ₀ +K ₁ lnSOC+K ₂ ln(1-SOC) of the open circuit voltage and the state of charge and the corresponding value of the open circuit voltage curve, the unknown parameters in the relational expression are obtained, and then The quantitative relationship between the open circuit voltage and the state of charge is obtained, where U _ocv is the open circuit voltage, SOC is the state of charge, and E ₀ , K ₁ , K ₂ are unknown parameters. 3. The battery energy efficiency measurement method according to claim 1 or 2, further comprising: After the charging or discharging is completed, the battery pack is left to stand still for a period of time. 4. The method for measuring battery energy efficiency according to claim 1, characterized in that the temperature of the battery pack in the step (2) and the step (3) is the same. 5. The method for measuring battery energy efficiency as claimed in claim 1, further comprising: Determine the charging system and discharging system according to the battery type; Discharge the remaining power of the battery pack according to the determined discharge system, then charge it to the charging cut-off voltage according to the determined charging system, and then discharge it to the discharge cut-off voltage according to the determined discharge system, and determine the discharged charge value as the battery pack. Rated Capacity. 6. The method for measuring battery energy efficiency as claimed in claim 1, wherein said step (4) further comprises: Charge the battery pack that has been fully discharged according to the determined discharge system with multiple different constant currents to the charging cut-off voltage, and then stop, and obtain the electric energy charged by the battery pack in any state of charge corresponding to each constant current; Then, the step (5) also includes: Determine the state of charge interval, and obtain the charging energy efficiency of the battery pack corresponding to each constant current; The charging energy efficiency of the battery pack corresponding to all constant currents is fitted by linear fitting or polynomial fitting, and the empirical formula of charging energy efficiency and current is obtained: η _charge =0.99121-0.04221×I+0.0082×I ² , where η _charge is the charge Energy efficiency, I is the current. 7. The method for measuring storage battery energy efficiency as claimed in claim 1, wherein said step (4) further comprises: Discharge the battery pack fully charged according to the determined charging system with multiple different constant currents to the discharge cut-off voltage, and then stop, and obtain the electric energy released by the battery pack corresponding to each constant current in any state of charge interval; Determine the state of charge interval, and obtain the discharge energy efficiency of the battery pack corresponding to each constant current; The discharge energy efficiency of the battery pack corresponding to all constant currents is fitted by linear fitting or polynomial fitting to obtain the empirical formula of discharge energy efficiency and current: _ηdisch =0.99722-0.04137×I+0.00344×I ² , where η _charge is Charging energy efficiency, I is the current.

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