eV – Field Status

Category

Successfully implemented Nations

Technology

2W

China

Lead-Acid ( VRLA) – 60% / LFP – 40%

3W

India/Bangladesh/Nepal/China

Flooded Tubular Battery- 95%/ LFP – 5%

4W

China

NMC/NCA/LFP

Lead vs Lithium (3W eV) - Reality check for Atmanirbhar product ( Indian context)

S.no

Parameters

Lead-Acid

Lithium

1

Local Manufacturing

Yes

Only Assembly/ Not Cell manufacturing

2

Local Material

Yes

Imported

3

Technology suitable to local eco system

Yes

Capital Expensive/ Not MSME friendly

4

Material shall be 100% recyclable

Yes

Not possible at present

5

Affordable to local eco system

Yes

3 times Costly

6

Product shall be suitable to local eco system

Yes

LFP is safe and NMC is prone to fire

7

Consistency in quality

Low

Good

8

Life of Battery

Low

Good

LFP in e-Rickshaw protocol (28+/- 3C)

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Benchmark target for LFP and Lead-Acid in e-Rickshaw protocol

S.No

Factors

Bench Mark

1

Total No. of cycles for LFP battery in laboratory

1300 cycles

2

Failure modes

SEI growth/ Lithium electro plating on anode

3

Realistic life in the field ( Hot summer/ Cold winter)

900 cycles

4

Lead-Acid Battery – 400 cycles

Red carpet to LFP. Lead Acid will be out from the market

5

Lead – Acid Battery – 400 to 600 cycles

LFP/LA can co-exist

6

Lead – Acid Battery – 600 to 900 cycles

LA will dominate

9

Lead – Acid Battery > 900 cycles

LFP will be out from the market

Reasons for 3W eV Lead acid battery failure vs Life in the field

Failure Modes

0 to 6 months

6 to 12 months

12 to 18 months

18 to 24 months

24 to 36 months

Manufacturing Defects

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Positive plate Defect

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Separator related failures

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Gauntlet related failures

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Inconsistency between the cells

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Positive active material shedding

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Positive spine corrosion

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Negative plate failure

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Manufacturing Defects

Type of Failure

Section

Type of Defects

What to attack

1) Manufacturing Defects

Assembly/ Group Burning section

Lead run down

1) Tool design 2) Operator’s skill

Plate disconnect

Lead piece

2) Positive plate Defect

Tube filling

Empty tube

1) Oxide nature/quality 2) Machine capability 3) Gauntlet quality

Tube loose

3) Separator related failures

Component/ Assembly

Separator puncture

Assembly/Enveloping/ plate design/plate handling

Separator Brittleness

Separator quality/Design

4) Gauntlet related failure

Component/Tube filling

Gauntlet bursting

Gauntlet quality – Nature of yarn, resin content, resin quality

Gauntlet damage

Plate handling

PAM leaching

Pore size and uniform distribution

5) Importance of Consistency

1

Typical e Rickshaw battery systems: 48V/100 Ah, 48V/120 Ah, 48V/150 Ah, 60V/120 Ah, 60V/150 Ah

2

A 48V system comprises 4 batteries in series. Each battery comprises of 6 cells. Hence, 24 cells are in series

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Battery – 1 (12V)

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Battery – 2 (12V)

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Battery – 3 (12V)

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Battery – 4 (12V)

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Battery Bank – ( 48V)

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3

Since 24 cells are in series, the lowest performer (lowest capacity) will determine system behaviour.

4

Capacity of cell is in turn related to weight of the plates

5

Variation in plate weight, or inconsistency in group weight, is one of the major reason for failure of battery

5) Importance of consistency - Reasons for Negative Plate Weight Variation

1

Machine capability of pasting machine ( Machine, type of belt, usage of belt)

2

Variation of negative paste density over the pasting duration; the pasting process lasts 45-60 mins, during which time density, moisture, and “pasteability” change. Material which can retain proper moisture during this period will improve consistency.

3

Is it possible to have the cured plate weight variation +/- 5 grams or even lower

4

Suppose if the process capability is +/- 8 grams and by other statistical tools how to bring down to +/- 3 grams

5) Importance of Consistency - Reasons for Positive Plate Weight Variation

1

Capability of tubular gauntlet filling machine ( Dry, Slurry, Paste filling)

2

Variation of tap density of blended oxide; most manufacturers buy oxide from multiple vendors, but controlling tap density of a blend is a major challenge.

3

Barton and Ball mill oxides are having different flow characteristics. Red lead% and oxide type will alter the consistency

4

Is it possible to have the tubular plate weight variation +/- 5 grams, or lower, without manual intervention?

5

Manual intervention / rework shall be avoided; this results in another type of failure mode due to density variation which is detrimental to life of battery

6

Suppose if the process capability is +/- 20 grams and by other statistical tools how to bring down to +/- 5 grams

5) Importance of Consistency - How to Reduce the Variation in Performance

S.No

Methodology

Practical implication

1

Built a new factory with very expensive machines

Commercially not feasible. Lithium industry adopted this approach because they started from scratch.

2

Segregate plates, and make batteries of various grades

Huge complication in manufacturing and will be a manufacturing nightmare

3

Segregate batteries based on capacity and grade the batteries

Reduces plant output, and also a manufacturing nightmare. In addition, it will be another nightmare from sales point of view. Lithium is doing this and hence plenty of spurious cells in the market

4

Reject/rework the plates falling out of specification

Reduces plant capacity and increases cost of manufacturing.

5

Use statistical tool/methodology

Will reduce variation to an order of 75% with minimal effort

6) Positive Active Material Shedding

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Beginning

During operation

End of Life

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6) Positive Active Material Shedding -How to Identify the Two Types of PAM having different electrochemical activity

Present analysis

Modified Analysis

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6) Positive Active Material Shedding

1

Delaying the disintegration of HFC active material and increasing buffer capacity duration

Add suitable PAM additive - 1

Optimise pack density

Improve oxide purity

2

Keep HFC passive material stable for long duration so that the buffer capability is more

Add suitable PAM additive -2

Select proper positive alloy

Optimise pack density

3

Altering ratio of HFC to LFC

PAM/NAM ratio

(PAM+NAM)/Acid ratio

Red lead/ Total oxide ratio, Oxide type

Oxide particle size

Charging methodology

7) Positive Spine Corrosion

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8) Negative Plate Failure: Sulphate Build-Up

1 hr

2 hrs

3 hrs

4 hrs

5 hrs

6 hrs

7 hrs

8 hrs

9hrs

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10 hrs

Due to the ON/OFF nature of the e-Rickshaw operation duty cycle, the negative plate is unable to fully recharge and always will have variety of non-uniform PbSO₄ crystals with different charge acceptance tendency

8) Negative plate Failure - Impact of Carbon During Overcharging in NAM

Carbon – Hydrogen atom storage capability

(H₂O splitter)

Electrolysis of H₂O to H2 and O2 leading to water Loss

2 H⁺ + 2 e^- H₂

Overall

H⁺ + e^- H_ad (RDS)

Volmer (Lead)

H_ad + H_ad H₂

H⁺ + e^- H_ad

Heyrovsky (Carbon)

H_ad + H⁺ + e- H₂ (RDS)

H⁺ + e^- H_ad

Tafel (Platinum)

H_ad + H_ad H₂ (RDS)

8) Negative plate Failure - How Atomic Hydrogen Prevent Lead sulphate formation

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During overcharging Heyrovsky additives and dCNT generates plenty of nascent Hydrogen atom. Hydrogen is captured in dCNT due to intercalation

During rest period after charging, the stored hydrogen acts as a capacitor. The chemically formed PbSO4 acts as a resistor in parallel. Internal shorting between Capacitor and Resistor results in reduction of PbSO4

PbSO₄ + 2H_ad Pb + H₂SO₄

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Additives having highest hydrogen atom storage capacity will effectively convert all PbSO4 in to Pb

dCNT due to its discrete nature has the highest hydrogen storage capacity and hence good PbSO4 recovery capability

8) Negative plate Failure -Stable Crystal Structure in Solar/eRickshaw Cycles:

Standard Carbon

With dCNT added to NAM (Sulphate Inhibitor)

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Long life e-rickshaw Lead-acid Battery – Game changer

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Conclusions

Positive plate Improvements

Optimise Type-A and Type-B behaviour using design and process methodology. Fix the Sanskar/DNA of a Battery

Use proper positive plate additives and alloy to strengthen Type-A active material from disintegration and improve the buffer capability when not in use

Use appropriate raw materials in proper ratio and fix the sanskar of a battery

Revisit battery design

Use appropriate SG of acid to maintain higher % of Type-B active material

Negative plate Improvements

Use Carbon/dCNT in a proper way along with proper expander to reduce sulphation and minimise water loss

Consistency in Battery/Cells

Maintain paste density of Negative paste through the pasting duration with special additive

Improve machine capability of pasting machine

Maintain tap density of blended oxide 24/7 duration in tube filling operation

Improve machine capability of tube filling machine

Use advanced statistical tools to reduce variation (+/- 3 g for NAM, +/5 g for PAM)

Conclusions

Manufacturing Defects

Adopt good manufacturing practices such as good tools/fixtures and have a good work force

Good quality positive plate

Have positive plate free from empty tube/Loose tube- Good quality oxide and good quality tube filling machine will ensure this

Separator related failures

A good quality separator in resonace with proper enveloping machine/ Assembly operation/ proper plate design/plate handling methodology will ensure this

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Gauntlet related Failures

Gauntlet quality – Proper yarn, resin content and resin quality along with proper assembly operation will ensure this

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Spine corrosion

Optimise spine casting conditions. Select proper alloy and grain refiner in such a way that the corrosion is uniform instead of grain boundary pattern. Use appropriate spine thickness and spine design.