Research of Battery Durability
Research of Ba,ery Durability Performance - Based on Lithium Ferrous Phosphate Battery
BYD Auto Industry Co., Ltd.
Oct., 2013
CONTENTS
目录
1
Topic
2
Features of Battery Durability Performance
3
Factors of Battery Durability Performance
4
Data of Current Vehicle Models
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Topic
Testing category
Material
Lithium Ferrous Phosphate
Vehicle model
Type
Bus
Pure electric vehicle
Passenger vehicle
Hybrid vehicle
Potassium manganate
NCM
BYD all research on Lithium Ferrous Phosphate Battery, implemented on
vehicles as bus K9 (pure EV), passenger car e6 (pure EV)
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Feature of Ba,ery Durability Performance
Six aspects are considered regarding parameter of
battery durability performance:
Capacity and energy
Storage
Ba,ery Durability Performance
DC internal resistance
Charging/
Discharging power
Dimension
Ba,ery safety
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Factors of Ba,ery Durability Performance Durability cycle testing shall be carried out based on five aspects below:
temperature
rate
cycle
charging/discharging depth
vibraFon
Different factors could influence each feature of battery durability performance
and different batteries will also have different performance. In order to explain
the researching method, following BYD research achievements will be
presented for battery durability performance.
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Ba,ery Durability Performance Research Case
• 
Ba<ery durability performance—capacity
Active discharging of pure electric
sedan high energy density battery
Active discharging of pure electric bus
high energy density battery
Room temperature(20℃ ± 5 ℃ ), testing cycle:
1、Refer to Standard QC/T 743 Lithium battery for EV;
2、Testing cycle: charge to 100% SOC with 0.5c constant current, and
then implement cycle standard discharging till reaching cut-off voltage;
3、With ratio of total output energy during cycles and initial energy,
convert into the cycles times in the graph.
4、Compare the influence to battery capacity fading under different cycle
conditions with the same output energy.
Battery cycle capacity fading is slightly slower than constant current cycle.
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Ba,ery Durability Performance Research Case
• 
Ba<ery durability performance—storage
Result analysis:
1、Under certain condition, battery capacity decrease regularly with storage time increase;
2、Under same storage temperature, capacity fading is faster when battery SOC is higher
after storage;
3、Under same SOC, capacity fading is faster when storage temperature is higher.
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Ba,ery Durability Performance Research Case
• 
Ba<ery durability performance—DC internal resistance(DCIR)
DCIR:when SOC is below 50%, voltage (produced when battery is discharging with 1.5C
constant current for 30s) is divided by discharging current
With battery capacity fading caused by cycles, battery DCIR changes regularly,
also with big fluctuation.
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Ba,ery Durability Performance Research Case
• 
Ba<ery durability performance—power
Room temperature(20℃ ± 5 ℃ ), testing cycle
1、 Refer to Standard QC/T 743 Lithium battery for EV;
2、Testing cycle: charge to 100% SOC with 0.5c constant current, and then implement
cycle standard discharging till reaching cut-off voltage;
3、Power: SOC below 50%, it is the power produced when battery is discharging with 1.5C
(300A) constant current for 30s.
With cycle condition at room temperature, SOC below 50%, battery power does not
change with battery capacity decrease.
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Ba,ery Durability Performance Research Case
• 
Ba<ery durability performance—temperature
Discharging @ Different temperature: fully charged at
room temp., then discharge after storage at different temp..
Charging @ Different temperature: fully discharged at
room temp., then charge after storage at different temp..
Ratio of charging/discharging capacity at different temp. and capacity at room temp. changes with
fading of battery capacity result analysis
1、Low temp. discharging capacity ratio gradually increase with fading of battery capacity, high
temp. discharging ratio increase slightly with fading of battery capacity but not obvious.
2、Low temp. charging capacity ratio gradually decrease with fading of battery capacity, high temp.
charging ratio gradually increase with fading of battery capacity.
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Ba,ery Durability Performance Research Case
• 
Ba<ery durability performance—rate
Different rate discharging: fully charged at room
temp., then discharge with different rate
Different rate charging: fully discharged at room
temp., then charge with different rate
Ratio of different rate charging/discharging capacity and 0.5C capacity change with
battery capacity fading result analysis:
1、With battery capacity fading, battery capacity ratio almost remains the same .
2、With battery capacity fading, battery capacity ratio decrease with rate increase when
high rate charging
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Data of Current Vehicle Models—Pure E-­‐Bus
Charging/discharging current data
Analysis:
After investigating charging /discharging current data of five BYD buses from
Shenzhen area for three months, charging/discharging current diagram above was
derived. Data above was categorized into several levels below:
Charging
rate
1/3C
1/6C
1/15C
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18%
9%
9%
Discharging
rate
1/3C
1/6C
1/15C
Ratio
11%
11%
42%
12
Data of Current Vehicle Models—Pure Electric
Passenger Vehicle
E6 Charging/discharging current data
Analysis:
After investigating charging /discharging current data of five BYD passenger
vehicles (Taxi) from Shenzhen area for three months, charging/discharging current
diagram above was derived. Data above was categorized into several levels below
(200AH cell):
Charging
rate
1/5C
1/2C
1C
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15%
19%
/
Discharging
rate
1/5C
1/2C
1C
Ratio
52%
12%
2%
13
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