IEC 62660-1：2010 Secondary lithium-ion cells for the propulsion of electric road vehicles –Part 1: Performance testing

试验项目

章节号

标准要求

Test temperature

4.4

If not otherwise defined, before each test the cell shall be stabilized at the test temperature for a minimum of 12 h. This period can be reduced if thermal stabilization is reached. Thermal stabilization is considered to be reached if after one interval of 1 h, the change of cell temperature is lower than 1 K.

Unless otherwise stated in this standard, cells shall be tested at room temperature using the method declared by the manufacturer.

General charge conditions

7.1

Unless otherwise stated in this standard, prior to electrical measurement test, the cell shall be charged as follows. Prior to charging, the cell shall be discharged at room temperature at a constant current described in Table 1 down to a end-of-discharge voltage specified by the manufacturer. Then, the cell shall be charged according to the charging method declared by the manufacturer at room temperature.

Capacity

7.2

Capacity of cell shall be measured in accordance with the following steps.

Step 1 – The cell shall be charged in accordance with 7.1.

After recharge, the cell temperature shall be stabilized in accordance with 4.4.

Step 2 – The cell shall be discharged at specified temperature at a constant current It (A) to the end-of-discharge voltage that is provided by the manufacturer. The discharge current and temperatures indicated in Table 1 shall be used.

NOTE Selective test conditions are shown in Table A.1 in Annex A.

The method of designation of test current It is defined in IEC 61434.

Step 3 – Measure the discharge duration until the specified end-of discharge voltage is reached, and calculate the capacity of cell expressed in Ah up to three significant figures.

SOC  adjustment

7.3

The test cells shall be charged as specified below. The SOC adjustment is the procedure to be followed for preparing cells to the various SOCs for the tests in this standard.

Step 1 - The cell shall be charged in accordance with 7.1.

Step 2 - The cell shall be left at rest at room temperature in accordance with 4.4.

Step 3 - The cell shall be discharged at a constant current according to Table 1 for (100 –n)/100 ´ 3 h for BEV application and (100 – n)/100 ´ 1 h for HEV application, where n is SOC (%) to be adjusted for each test.

Power

7.4

7.4.1 Test method

The test shall be carried out in accordance with the following procedure.

a) Mass measurement

 Mass of the cell shall be measured as specified in Clause 6.

b) Dimension measurement

Dimension of the cell shall be measured as specified in Clause 5.

c) Current-voltage characteristic test

Current-voltage characteristics shall be determined by measuring the voltage at the end of the 10 second pulse, when a constant current is discharged and charged under the conditions specified below.

1) SOC shall be adjusted to 20 %, 50 %, and 80 % according to the procedure specified in 7.3.

2) The cell temperature at test commencement shall be set to 40 °C, 25 °C, 0 °C, and –20 °C.

3) The cell is charged or discharged at each value of the current corresponding to the respective rated capacity level, and the voltage is measured at the end of the 10 s pulse. The range of the charge and discharge current shall be specified by the manufacturer, and the standard measurement interval shall be 1 s. If the voltage after 10 s exceeds the discharge lower limit voltage or charge upper limit voltage, the measurement data shall be omitted.

NOTE The charge/discharge limits at low temperature specified by the manufacturer should be taken into account.

Table 2 shows examples of charge and discharge current according to the applications. If it is required, the maximum current for charge and discharge is specified by the cell manufacturer (Imax). This value can be reduced according to the agreement with the customer. The maximum charge and discharge current can be applied after the measurement at 5 It for BEV application and 10 It for HEV application. Imax value changes depending on SOC, test temperature and charge or discharge state.

Table 2 – Examples of charge and discharge current

4) 10-min rest time shall be provided between charge and discharge pulses as well as between discharge and charge pulses. However, if the cell temperature after 10 min is not within 2 K of test temperature, it shall be cooled further; alternatively, the rest time

duration shall be extended and it shall be inspected whether the cell temperature then settles within 2 K. The next discharging or charging procedure is then proceeded with.

5) The test is performed according to the scheme shown in Figure 3a and Figure 3b.

NOTE 1 Selective test conditions are shown in Table A.2 in Annex A.

NOTE 2 The current-voltage characteristic line can be obtained by straight-line approximation using the measured values of current and voltage, from which Imax and power can be calculated. The slope of this line shows the internal resistance of cell

7.4.2 Calculation of power density

7.4.2.1 Power

The power shall be calculated according to equation (1) and rounded to 3 significant figures.

P_d=U_d×I_dmax                                    （1）

where

Pd is the power (W);

Ud is the measured voltage at the end of the 10 s pulse of Idmax discharge (V);

Idmax is the maximum discharge current which is specified by the manufacturer (A).

If Pd is an estimated value, it shall be stated.

7.4.2.2 Power density per unit mass

Mass power density is calculated from equation (2), and is rounded to 3 significant figures.

Ρ_pd=        （2）

where

Ρ_pd is the power density (W/kg);

Pd is the power (W);

m is the mass of cell (kg).

7.4.2.3 Power density per unit volume

Volumetric power density shall be calculated from equation (3), and is rounded to 3 significant figures.

Ρ_pvlm=    (3)

where

Ρ_pvlm is the volumetric power density (W/l);

Pd is the power (W);

V is the volume of cell (l).

The volume of a prismatic or a flat cell is given by the product of its total height excluding terminals, width, and length, and that of a cylindrical cell is given by the product of the cross section of the cylinder and its total length excluding terminals.

7.4.3 Calculation of regenerative power density

7.4.3.1 Regenerative power

Regenerative power shall be calculated according to equation (4) and rounded to three significant figures.

P_c=U_c×I_cmax                   （4）

where

Pc is the regenerative power (W);

Uc is the measured voltage at the end of the 10 s pulse of Icmax charge (V);

Icmax is the maximum charge current specified by the manufacturer (A).

If Pc is an estimated value, it shall be stated.

7.4.3.2 Regenerative power density per unit mass

Regenerative power density per unit mass shall be calculated from equation (5) and is rounded to three significant figures.

Ρ_pc=               (5)

where

Ρ_pc is the regenerative power density (W/kg);

Pc is the regenerative power (W);

m is the mass of cell (kg).

7.4.3.3 Regenerative power density per unit volume

Volumetric regenerative power density is calculated from equation (6) and is rounded to three significant figures.

Ρ_pvlmc=           （6）

where

Ρ_pvlmc is the volumetric regenerative power density (W/l);

Pc is the regenerative power (W);

V is the volume of cell (l).

The volume of a prismatic or a flat cell is given by the product of its total height excluding terminals, width, and length, and that of a cylindrical battery is given by the product of the cross section of the cylinder and its total length excluding terminals.

Energy

7.5

7.5.1 Test method

Mass energy density (Wh/kg) and volumetric energy density (Wh/l) of cells in a certain current discharge of 1/3 It A for BEV application and 1 It A for HEV application shall be determined according to the following procedure.

a) Mass measurement

Mass of the cell shall be measured as specified in Clause 6.

b) Dimension measurement

Dimension of the cell shall be measured as specified in Clause 5.

c) Capacity measurement

Capacity of the cell shall be determined in accordance with 7.2 at room temperature.

d) Average voltage calculation

The value of the average voltage during discharging in the above capacity test shall be obtained by integrating the discharge voltage over time and dividing the result by the discharge duration. The average voltage is calculated in a simple manner using the following method: Discharge voltages U1, U2, …, Un are noted every 5 s from the time the discharging starts and voltages that cut off the end of discharge voltage in less than 5 s are discarded. The average voltage Uavr is then calculated in a simplified manner using equation (7) up to three significant figures by rounding off the result.

U_avr=（U₁+U₂+…U_n）/n                    (7)

NOTE Values provided by measurement devices may be used, if sufficient accuracy can be achieved.

7.5.2 Calculation of energy density

7.5.2.1 Energy density per unit mass

The mass energy density shall be calculated using equation (8) and equation (9) up to three significant figures by rounding off the result.

Wed = CdUavr        (8)

Wed is the electric energy of cell (Wh);

Cd is the discharge capacity (Ah) at 1/3 It (A) for BEV or 1 It (A) for HEV;

Uavr is the average voltage during discharging (V).

Ρ_ec=                (9)

where

Ρ_ec is the mass energy density (Wh/kg);

Wed is the electric energy of cell (Wh);

m is the mass of cell (kg).

7.5.2.2 Energy density per unit volume

The volumetric energy density shall be calculated using equation (10) up to three significant figures by rounding off the result.

Ρ_evlmc=                  (10)

where

Ρ_evlmc is the volumetric energy density (Wh/l);

Wed is the electric energy of cell (Wh);

V is volume of cell (l).

The volume of prismatic cell shall be given by the product of the total height excluding terminals, width, and length of the cell, and that of cylindrical cells shall be given by the product of the cylindrical cross-sectional area and the total length excluding terminals.

Storage test

7.6

7.6.1 Charge retention test

The charge retention characteristics of cell at a 50 % SOC shall be determined according to

the following procedure.

Step 1 - The cell shall be charged in accordance with 7.1.

Step 2 - The cell shall be discharged to 50 % SOC in accordance with the method specified in

7.3. Then, the cell shall be stabilized at test temperature for 1 h.

Step 3 - Discharge the cell to the end-of-discharge voltage at a discharge current of 1/3 It (A)

for BEV application and 1 It (A) for HEV application and at room temperature. This discharge

capacity is Cb.

Step 4 - Repeat steps 1 and 2.

Step 5 - The cell shall be stored for 28 days at an ambient temperature 45 °C ± 2 K.

Step 6 - Discharge the cell at a constant current of 1/3 It (A) for BEV application and 1 It (A)

for HEV application at room temperature until end-of-discharge voltage, and then measure the

capacity of cell. This discharge capacity is Cr.

Charge retention ratio shall be calculated according to equation (11).

R= ×100          （11）

where

R is the charge retention ratio (%);

Cr is the capacity of cell after storage (Ah);

Cb is the capacity of cell before storage (Ah).

7.6.2 Storage life test

The storage life of a cell shall be determined according to the following procedure.

Step 1 - Determine the capacity, power density and regenerative power density of cell in accordance with 7.1, 7.2 and 7.4.

Step 2 - Adjust the SOC of cell to 100 % for BEV application, and to 50 % for HEV application in accordance with 7.3. The cell shall then be stored for 42 days at an ambient temperature 45 °C ±2 K.

Step 3 - Following the storage of step 2, the cell shall be kept at room temperature according to 4.4 and discharged at a constant current of 1/3 It (A) for BEV application and 1 It (A) for HEV application, down to the end-of discharge voltage specified by the manufacturer. Then, measure the capacity of cell. This discharge capacity is the retained capacity (Ah).

Step 4 - Repeat step1, step 2 and step 3 for 3 times.

 The capacity, power density, regenerative power density and retained capacity measured in step1 and step 3 shall be reported.

If the cell is stored at room temperature during the test for rest such as for test timing adjustment, the total time of such rest shall be reported.

Cycle life test

7.7

The cycle life test shall be performed to determine the degradation character of cell by charge and discharge cycles.

NOTE 1 The cycle life test sequence is shown in Annex B.

NOTE 2 Selective test conditions are shown in Table A.3 in Annex A.

7.7.1 BEV cycle test

The cycle life performance of cell for BEV application shall be determined by the following test methods.

7.7.1.1 Measurement of initial performance

Before the charge and discharge cycle test, measure the capacity, dynamic discharge capacity, and power as the initial performance of cell.

– Capacity

The capacity shall be measured as specified in 7.2 at 25 °C ± 2 K.

– The dynamic discharge capacity CD

The dynamic discharge capacity CD shall be measured at 25 °C ± 2 K and 45 °C ± 2 K.

The dynamic discharge capacity is defined by the time integrated value of charge and discharge current confirmed by the following test: Discharge the fully charged cell repeatedly by the dynamic discharge profile A specified in Table 3 and Figure 4 until the voltage reaches the lower limit specified by the manufacturer.

– Power

The power shall be measured as specified in 7.4 at 25 °C ± 2 K, 50 % SOC.

7.7.1.2 Charge and discharge cycle

The charge and discharge cycle test shall be performed as follows.

a) Temperature

The ambient temperature shall be 45 °C ± 2 K. At the start of charge and discharge cycle, cell temperature shall be 45 °C ± 2 K.

b) Charge and discharge cycle

A single cycle is determined as the repetition of the following steps from 1 to 4. The rest time between each step shall be less than 4 h.

The cycle shall be continuously repeated for 28 days. Then, measure the performance of the cell as specified in 7.7.1.2 c). This procedure shall be repeated until the test termination specified in 7.7.1.2 d).

Step 1 - The cell shall be fully discharged by the method specified by the manufacturer.

Step 2 - The cells shall be fully charged by the method specified by the manufacturer. The charge time shall be less than 12 h.

Step 3 - Discharge the cell following the dynamic discharge profile A specified in Table 3 and Figure 4 until the discharged capacity reaches equivalent to 50 % ± 5 % of the initial dynamic discharge capacity CD at 45 °C.

If the voltage reaches the lower limit specified by the manufacturer during step 3, the test shall be discontinued notwithstanding the stipulation in 7.7.1.2 d), and the cell performance shall be measured at this point as specified in 7.7.1.2 c).

If the temperature of cell reaches the upper limit specified by the manufacturer during step 3, the duration of charge/discharge step 20 in Table 3 can be extended to an appropriate value. The actual duration time shall be reported.

In this profile, the test power shall be calculated using equation (12)

Pmax = N Wed     (12)

where

Pmax is the test power (W);

N is a value (1/h) of vehicle required maximum power of cell (W) divided by energy of cell (Wh);

NOTE The value of N = 3/h is an example based on the specifications of commercialized BEVs.

Wed is the electric energy of cell at room temperature (Wh).

If the value derived from equation (12) is larger than the maximum power of cell specified by the manufacturer, the test power shall be defined as 80 % of the maximum power at room temperature and at 20 % SOC specified by the manufacturer. Power value actually used shall be reported.

Figure 4 – Dynamic discharge profile A for BEV cycle test

Step 4 - Discharge the cell following the dynamic discharge profile B (hill climbing profile) specified in Table 4 and Figure 5 for one time. The test power shall be calculated using equation (12).

If the voltage reaches the lower limit specified by the manufacturer during step 4, the test shall be discontinued notwithstanding the stipulation in 7.7.1.2 d), and the cell performance shall be measured at this point as specified in 7.7.1.2 c).

If the battery voltage frequently reaches the lower limit voltage during charge/discharge step 16, the discharge power and duration can be changed appropriately. The actual test values shall be reported accordingly.

Table 4 – Dynamic discharge profile B for BEV cycle test

Figure 5 – Dynamic discharge profile B for BEV cycle test

Step 5 - Discharge the cell following the dynamic discharge profile A specified in Table 3 and Figure 4 until the overall discharge capacity including step 3 and step 4 reaches equivalent to 80 % of initial CD at 45 °C.

If the temperature of cell reaches the upper limit specified by the manufacturer during step 5, the duration of charge/discharge step 20 in Table 3 can be extended to an appropriate value. The actual duration time shall be reported.

If the voltage reaches the lower limit specified by the manufacturer during step 5, the test shall be discontinued notwithstanding the stipulation in 7.7.1.2 d), and the cell performance shall be measured at this point as specified in 7.7.1.2 c).

c) Periodical measurement of performance

After every completion of the repetition from step 1 to step 5 for 28 test days, the performance

of cell shall be measured as specified in 7.7.1.1. The accumulated time from step 1 to step 4 in 7.7.1.2 b) shall also be reported. The dynamic discharge capacity shall be measured at 25 °C ± 2 K only.

d) Termination of test

The cycle life test shall be terminated when either of the following conditions is satisfied. Otherwise back to 7.7.1.2 a) and repeat the test.

Condition A – The test sequence from 7.7.1.2 a) to 7.7.1.2 c) is repeated 6 times.

Condition B – When any of the performance measured in 7.7.1.2 c) is decreased to less than 80 % of the initial value.

Condition C – The temperature of cell reaches the upper limit agreed between the manufacturer and the customer during the test.

The number of implemented times of each profile and cycle during the test shall be reported.

7.7.2 HEV cycle test

The cycle life performance of cell for HEV application shall be determined by the following test methods.

7.7.2.1 Measurement of initial performance

Before the charge and discharge cycle test, measure the capacity and power as the initial performance of cell.

– Capacity

The capacity shall be measured as specified in 7.2 at 25 °C ± 2 K.

– Power

The power shall be measured as specified in 7.4 at 25 °C ± 2 K, 50 % SOC.

7.7.2.2 Profile switching voltage

Before the cycle life test, set switching voltages at which discharge-rich profile and chargerich profile specified in 7.7.2.3 c) shall be switched over.

a)     Switching voltage from discharge-rich profile to charge-rich profile

Adjust the SOC of cell to 30 % according to 7.3, and then perform the cycle test with discharge-rich profile at 45 °C for one time. The lowest voltage achieved during this test shall be the switching voltage from discharge-rich profile to charge-rich profile. If the achieved lowest voltage is lower than the manufacturer’s specified lower limit voltage, the latter shall be the switching voltage. The manufacturer's recommended SOC of cell may be used additionally.

b) Switching voltage from charge-rich profile to discharge-rich profile

Adjust the SOC of cell to 80 % according to 7.3, and then perform the cycle test with charge rich profile at 45 °C for one time. The highest voltage achieved during this test shall be the switching voltage from charge-rich profile to discharge-rich profile. If the achieved highest voltage is higher than the manufacturer’s specified upper limit voltage, the latter shall be used as switching voltage. The manufacturer's recommended SOC of cell may be used additionally.

7.7.2.3 Charge and discharge cycle

The charge and discharge cycle test shall be performed as follows.

a) Temperature

The ambient temperature shall be maintained at 45 °C ± 2 K in accordance with 4.4 during the test. At the start of charge and discharge cycle, cell temperature shall be 45 °C ± 2 K in accordance with 4.2.4.

b) Adjustment of SOC before charge and discharge cycle

The cells shall be left at a temperature of 45 °C ± 2 K, and be adjusted to 80 % SOC or the SOC agreed between the manufacturer and the customer within an interval of 16 h to 24 h, in accordance with 7.3. If 80 % SOC is not used, the used SOC shall be reported.

c) Charge and discharge cycle

The procedure from step 1 to step 4 shall be continuously repeated until the test termination specified in 7.7.2.3 e). During the test, the performance of the cell shall be measured periodically as specified in 7.7.2.3 d).

If the temperature of cell reaches the upper limit specified by the manufacturer during the test, the duration of charge/discharge step 16 in Table 5 and Table 6 can be extended to an appropriate duration time. The actual duration time shall be reported.

Step 1 - Charge and discharge cycle shall be carried out repeatedly through the dischargerich profile given by Table 5 and Figure 6 until the cell voltage reaches to the switching

voltage set in 7.7.2.2 a) (see Figure 8).

Step 2 - Charge and discharge cycle shall be carried out repeatedly through the charge-rich profile given by Table 6 and Figure 7 until the cell voltage reaches to the switching voltage set in 7.7.2.2 b) (see Figure 8).

Step 3 - Repeat step 1 and step 2 for 22 h.

Step 4 - Rest the cell for 2 h.

Table 5 – Discharge-rich profile for HEV cycle test

Figure 6 – Discharge-rich profile for HEV cycle test

If the maximum current specified by the manufacturer is below 20 It, the manufacturer's specified maximum current may by used at charge/discharge step 1, along with replacing the current at charge/discharge step 6 with 1/2 of the manufacturer's specified maximum current.

Table 6 – Charge-rich profile for HEV cycle test

Figure 7 – Charge-rich profile for HEV cycle test

If the maximum current specified by the manufacturer is below 20 It, the manufacturer's specified maximum current may by used at charge/discharge step 5, along with replacing the current at charge/discharge step 2 with 1/2 of the manufacturer's specified maximum current.

Figure 8 – Typical SOC swing by combination of two profiles for HEV cycle test

d) Periodical measurement of performance

After every completion of the procedure from step 1 to step 4 for 7 days, the power of cell shall be measured as specified in 7.7.2.1. The capacity of cell shall be measured every 14 days as specified in 7.7.2.1.

e) Termination of test

The cycle life test shall be terminated when either of the following conditions is satisfied. Otherwise back to 7.7.2.3 a) and repeat the test.

Condition A – The test in 7.7.2.3 c) is repeated for a total of 6 months.

Condition B – When either of the performance measured in 7.7.2.3 d) is decreased to less than 80 % of the initial value.

The number of times of each profile implementation and that the switching voltages are reached shall be reported.

Energy efficiency test

7.8

Energy efficiency of cells shall be determined by two common tests as specified in 7.8.1 and either of tests described in 7.8.2 and 7.8.3.

7.8.1 Common tests

7.8.1.1 Test for normal conditions

This test is applicable to cells used in HEVs and BEVs. The test shall be carried out in accordance with the following procedure.

a) The cell shall be left at rest at room temperature for a minimum of 1 h and a maximum of 4 h after full charge. The test shall then be commenced.

b) Discharge the cell by the method specified in 7.2 at room temperature.

c) Energy efficiency test at 100 % SOC:

1) leave the cell at rest for 4 h, and then charge it to 100 % SOC by the method recommended by the manufacturer;

2) leave the cell at rest for 4 h, and then discharge it by the method specified in 7.2 at room temperature.

d) Energy efficiency test at 70 % SOC:

1) leave the cell at rest for 4 h, and then charge it to 70 % SOC by the method recommended by the manufacturer;

2) leave the cell at rest for 4 h, and then discharge it by the method specified in 7.2 at room temperature.

e) Calculation of the discharge electric quantity and charge electric quantity

The electric quantity during the discharge and charge can be calculated using the following method: read the discharge and charge currents I at intervals of s seconds (s ≤ 30) from the start of the discharge; then, calculate the discharge electric quantity Qd and charge electric quantity Qc using equation (13).

Q=                (13)

where

Q is discharge electric quantity or charge electric quantity (Ah);

In is discharge current value or charge current value at n point of measured intervals (A).

f) Calculation of the discharge electric energy and charge electric energy.

The electric energy during the discharge and charge can be calculated using the following method: read the discharge currents I and the discharge voltages V at intervals of s seconds (s ≤ 30) from the start of discharge; then, calculate the discharge electric energy and charge electric energy using equation (14).

W=                (14)

where

W is discharge electric energy or charge electric energy (Wh);

In is charge current value or discharge current value at n point of measured intervals (A);

Un is discharge voltage value at n point of measured intervals (V).

g) Calculation of energy efficiency

Determine the coulomb efficiency using equation (15) and the energy efficiency using equation (16).

η_c = 100        (15)

where

ηc is coulomb efficiency (%);

Qd is discharge electric quantities in 7.8.1 (Ah);

Qc is charge electric quantities in 7.8.1 (Ah).

η_e= 100           (16).

where

ηe is energy efficiency (%);

Wd is discharge electric energies in 7.8.1 (Wh);

WC is charge electric energies in 7.8.1 (Wh).

NOTE Values provided by measurement devices may be used, if sufficient accuracy can be achieved.

7.8.1.2 Test by temperature

This test is applicable to cells used in HEVs and BEVs. The test shall be carried out in accordance with the following procedure.

The test shall be carried out at the test temperatures of –20 °C ± 2 K, 0 °C ± 2 K, and 45 °C ± 2 K.

a) Full charge at room temperature.

b) Thermal equilibration of the cell at the test temperature, and start testing after a minimum of 16 h and a maximum 24 h.

c) Discharge the cell by the method specified in 7.2 at each test temperature.

d) Energy efficiency test at 100 % SOC:

1) at each test temperature, leave the cell at rest for 4 h, and then charge it to 100 % SOC by the method recommended by the manufacturer;

2) leave the battery at rest for 4 h, and then discharge it by the method specified in 7.2.

e) Calculate discharge electric quantity and charge electric quantity using equation (13).

f) Calculate discharge electric energy and charge electric energy using equation (14).

g) Calculate coulomb efficiency and energy efficiency using equation (15) and equation (16).

NOTE The charge/discharge limits at low temperature specified by the manufacturer should be taken into account.

7.8.2 Test for cells of BEV application

This test is applicable to cells used in BEVs, and intended to determine the energy efficiency of cells under fast charging conditions. The test shall be carried out in accordance with the following procedure.

a) The cell shall be left at rest at room temperature for a minimum of 1 h and a maximum of 4 h after full charge. The test shall then be commenced.

b) Discharge the cell by the method specified in 7.2.

c) Energy efficiency test at 80 % SOC:

1) leave the cell at rest for 4 h, and then charge it to 80 % SOC at 2 It. If the voltage reached the upper limit voltage specified by the manufacturer, charging shall be terminated;

NOTE Selective test conditions are shown in Table A.4 in Annex A.

2) leave the cell at rest for more than 4 h until the cell has attained the test temperature, and then discharge it by the method specified in 7.2.

d) Calculate discharge electric quantity and charge electric quantity using equation (13).

e) Calculate discharge electric energy and charge electric energy using equation (14).

f) Calculation of energy efficiency.

Determine the Coulomb efficiency using equation (17) and the energy efficiency using equation (18).

η_c1= 100                       （17）

where

ηc1 is coulomb efficiency (%);

Qd1 is discharge electric quantities in 7.8.2 (Ah);

Qc1 is charge electric quantities in 7.8.2 (Ah).

Η_e1= 100                       （18）

where

ηe1 is energy efficiency (%);

Wd1 is discharge electric energies in 7.8.2 (Wh);

Wc1 is charge electric energies in 7.8.2(Wh).

7.8.3 Energy efficiency calculation for cells of HEV application

This paragraph is applicable to cells used in HEVs.

a) Calculation of the charge electric energy and discharge electric energy.

Calculate the charge and discharge electric energy from the results of the test specified in 7.4 using equation (19) and equation (20). Round off the resulting values to three significant figures.

Read current values and voltage values at regular intervals from the current and voltage data collected during the charge and discharge cycles, which correspond to the charge and

discharge patterns of duration 10 It × 10 s. Use the standard measurement interval of 1 s. When the battery voltage after 10 s exceeds the discharge lower limit voltage or the charge

upper limit voltage, perform the test using the current value in the lower stage of Table 1, and report the current value that was actually observed.

W_c2=        (19)

where

WC2 is charge electric energy (Wh);

Icn is charge current value at n point of measured intervals (A);

Ucn is charge voltage value at n point of measured intervals (V).

W_d2=        (20)

where

Wd2 is discharge electric energy (Wh);

Idn is discharge current value at n point of measured intervals (A);

Udn is discharge voltage value at n point of measured intervals (V).

b) Calculation of energy efficiency

Determine the energy efficiency using equation (21).

ηe2= 100             （21）

where

ηe2 is energy efficiency (%);

Wd2 is discharge electric energy (Wh);

WC2 is charge electric energy (Wh).