Product Engineering Daimler Buses High-Voltage Battery · Conclusion Good trade-off between range and charging power. Different operating concepts can be realized. Best suited for

Developing the battery for an electric city bus

Frieda M. DaveyProduct Engineering Daimler Buses – High-Voltage Battery

Developing the battery for an electric city bus | Daimler Buses | Frieda M. Davey


Daimler Buses

Daimler

Trucks

Mercedes-Benz

Cars

Mercedes-Benz

Vans

Daimler

Buses

Daimler

Financial

Services

Revenue 2018

Employees 2018

Daimler Buses – A business unit of the Daimler Group

€ 26.3 Mrd.

14,070145,436

€ 93.1 Mrd.

82,953

€ 38.3 Mrd.

26,210

€ 13.6 Mrd.

18,770

€ 4.5 Mrd.

Annotation: Revenue company 2018: € 167,4 bn., Employees: 298,683

Developing the battery for an electric city bus | Daimler Buses | Frieda M. Davey Seite 3

http://upload.wikimedia.org/wikipedia/commons/a/a5/Car2go_logo.svg

http://www.setra.de/setrastartseite.html

Daimler Buses

City buses

Page 4

Interurban buses

Coaches

Minibuses

Product Portfolio

The Mercedes-Benz product range at a glance

Citaro* Conecto NGT + Conecto G NGTCapaCity + CapaCity L

Sprinter City

Citaro Ü*Intouro

Tourismo RHTourismoTourismo K

Sprinter TransferSprinter Travel

Citaro LE Ü*

Citaro NGT* + Citaro G NGT*

Sprinter Mobility

Conecto + Conecto G

Citaro GÜ * available as hybrid

Citaro LE*


Daimler Buses

City and interurban buses

Page 5

City and interurban buses

Tour coaches

rear engine chassis

front engine chassis

rear engine chassis

Product portfolio

Mercedes-Benz chassis

* CBC = City Bus Concept (O500 also available as RF O500 M/MA/MDA)

** XBC Flexible Bus Concept

*** IBC = Intercity Bus Concept

OC 500 LE (CBC - LE)* O 500 U (CBC-LE)* OH RF (XBC)**

OF LO Boxer

O 500 RS (IBC)***OC 500 RF (IBC)***

O 500 UA

(CBC-LE-Gelenkzug)*

O 500 UDA

(CBC-LE-CapaChassis)*

O 500 RSD (IBC)*** O 500 RSDD (IBC)***


Daimler Buses Page 6

Mercedes-Benz

Türk

Daimler

Buses

Mexico

EvoBus

Group

Daimler

Buses

Latin

America

Daimler Entities

Bus

Indonesia

Australia

South Africa

Daimler Buses

India

Daimler Buses - globally present

Our production sites are present all over the world


Public transport needs to become more attractive at reduce

CO2 footprint and emissions at the same time.

Increasing mobility needs

Inner-city densification

Limited traffic areas

Noise pollution

Individual transport at its limits

Emission limits

Environmental zones and

access restrictions

CO2 targets (national / local)

Public funding for e-mobility

High pollution levels in cities

Public traffic needs to be part

of the solution

Need for ActionMobility Trends Legal & Political Premises

Developing the battery for an electric city bus | Daimler Buses | Frieda M. Davey Page 77


PL 2025: 30% zero

emission

SE 2030: min.

regenerative fuel

FR 2025: 100% low emission zones

(Cities > 250.000 population)

NL 2025-30: 100%

zero emission

Source: customer interviews, press, market studies

Seite 8

DNK 2030: 100%

zero emission

1 by 1 Transformation of Diesel- to e-Buses not feasible by today

Developing the battery for an electric city bus | Daimler Buses | Frieda M. Davey 9

Target picture

e.g. 2025

Lower Range of Electric Buses compared to

Diesel Buses

Modification of Operation Concepts needed

Charging Systems & Interfaces to be developed

Setup of Energy Supply and Charging

Infrastructure

Standardization to be defined

Redesign of Processes required

(e.g. Service and Maintenance)

Training and Qualification

Financial Constraints

Etc.

Challenge 1: E-Buses carry only a fraction of the energy of a diesel bus.

At the same time, the weight is higher.


Diesel Bus

Tank capacity: ~ 215 l diesel

Weight: ~ 200 kg

Energy:

~ 2,100 kWh

Electric Bus

6 – 12 High-voltage batteries

Weight: ~ 1.500 – 3.000 kg

Energy:

~ 150 - 300 kWh

Challenge 2: Pure driving is possible with very little energy. Heating and

air-conditioning drastically increase the energy consumption.


En

erg

y c

on

su

mp

tio

n

Pure

Driving

Cooling

(Summer)

Heating

(Winter)

Energy consumption

nearly doubles

During winter, warm air flows out of the bus at every stop

while cold air enters.

Hence the energy needed for heating is very high.

In summer, air-conditioning leads to similar effects.

Challenge 3: The depot needs a completely different electricity supply

infrastructure to charge a fleet of electric buses.


150 kW

One charging station

for an electric bus

has a similar power

demand as 75

households.

75

Transformer

Medium voltage

10 – 30 kV

Depots for electric buses are

directly connected to the medium

voltage grid and need

transformers on the depot.

5 -10 min

2 – 5 h

Charging of an electric bus

requires several hours. For this,

all processes in the depot need

to be adapted..

Challenge 4: Various battery types with different properties and

development roadmaps are available


Battery TypeNMC(Nickel-Manganese-Cobalt)

Solid-State (Lithium-Metal-Polymer)

LFP(Lithium-Iron-Phosphate)

LTO(Lithium-Titanate-Oxide)

Charging power + + + + + + + +

Driving range + + + + 0 -

Service life + + + + + + +

Conclusion

Good trade-off between

range and charging

power. Different

operating concepts can

be realized.

Best suited for

overnight charging

concepts with long daily

runs thanks to high

capacity.

Similar to NMC but

lower range at given

weight. Higher self-

discharge causes

balancing issues.

Only suitable for

opportunity charging

concepts with very

short distances and fast

recharging.

Comparison of different offers difficult

Selection of suitable operating concept for battery type

How does the future look like Can the battery be upgraded?

Challenge 5: E-Bus workshops require new equipment and staff training.


Roof working structure

Crane system

Testing and charging equipment

Safety equipment

HV sensibilization

Specialist for HV vehicles

Working under voltage

Responsible electrician for HV systems

Energy Efficiency

Main development focus was modularity and energy efficiency


Modularity and FlexibilityProject Status

low

highBattery Capacity

Charging OptionsPanto-

graph

CCS

Plug

Transition

Period

Summer Winter

Driving Auxiliaries Heating Cooling

Thermal Management

Energy ManagementHeating

Cooling

Maximum Range

Start of Delivery

Solo: Q1/2019

Articulated: Q2/2020

Solo RHD: Q4/2021

~88 ~130

Vehicle Type

Daimler Buses

Bild vom EDB und Kerndaten


Our first step in electrification

of public transport

as platform for eMobility

The new Mercedes-Benz eCitaro

A sophisticated starting point of an eMobility platform

• 8 t front axle • Modular

battery

clusters

• Rear axle

with 2 electric motors close to wheel hub

• Battery cooling system

• Cooling system for drivetrain and auxiliaries

• CO2 air conditioning with heat pump


Customer operations

with major deviations

• Operation area

• Line topography

• Infrastructure

• Operational processes

Charging systems

Depot or opportunity charging

Vehicle preparation and service

Evaluation of customer requirements

Requires more than a singular technology approach


infrastructure,

charging systems

Operation area

inner city

outer city

…

suburbs

Technology roadmap considers availability and maturity

Portfolio will significantly grow in 2020 to cover majority of demands


Vehicle

Charging system

+

+

Battery system

+



Secondary cell


Cathode matrix

Anode matrix

Cathode Separator Anode

Liquid electrolyte

Discharge

Daimler Buses

Cell chemistries – an overview


Lithium-Sulphur Battery

Energiedichte (wg. Lithium)

Leistungsdichte

Schnellladen

Zyklenfestigkeit

Sicherheit

Kosten

Nachhaltigkeit

All Solid-State Battery

Energiedichte (v. a. Lithium)

Leistungsdichte

Schnellladen

Zyklenfestigkeit

Sicherheit

Kosten

Nachhaltigkeit

LIB with Li-Metal-Anode

Energiedichte (insb. Wh/l gering)

Leistungsdichte

Schnellladen

Zyklenfestigkeit

Sicherheit

Kosten

Nachhaltigkeit

Maturity: high - industrialized Maturity: low - developmentMaturity: very low - researchMaturity: low - development

Lithium-Ion-Battery (LIB)

EV, EES, Electronics, Drones Aviation, EES, possibly EVsPossibly EVsDrones, Electronics, (possibly EVs)

Li-Metal-Polymer-Battery

Energiedichte

Leistungsdichte

Schnellladen

Zyklenfestigkeit

Sicherheit

Kosten

Nachhaltigkeit

Maturity: intermediate

EV, EES

Cathode matrix

Anode matrix


Load

Liquid electrolyte

Discharge

• Energy density

• Power density

• Fast charging

• Cyclability

• Safety

• Cost

• Sustainability

• Energy density

• Power density

• Fast charging

• Cyclability

• Safety

• Cost

• Sustainability

Cathode matrix

Lithium metal Discharge

Load


Liquid electrolyte Protection layer

Cathode matrix

Lithiated cath. Discharge

Cathode Anode

Inorganic solid electrolyte = separator

Aode

• Energy density

• Power density

• Fast charging

• Cyclability

• Safety

• Cost

• Sustainability

Cathode matrix

Lithium Sulphide. Discharge

Load Load Load


Liquid electrolyte

• Energy density

• Power density

• Fast charging

• Cyclability

• Safety

• Cost

• Sustainability

Cathode matrix

Lithiated cath. Discharge

Cathode Anode

Polymer solid electrolyte = separator

• Energy density

• Power density

• Fast charging

• Cyclability

• Safety

• Cost

• Sustainability

Daimler Buses

LIB - Typical cathode materials

• NMC Lithium-Nickel-Manganese-Cobalt-Oxid

• LMO Lithium-Manganese-Oxide

• LFP Lithium-Iron Phosphat

• NCA Lithium-Nickel-Cobalt-Aluminium-Oxide

• …


Cathode matrix

Anode matrix


Liquid electrolyte

Discharge

Daimler Buses

LIB - Typical Anode Materials

• Graphite with intercaleted Li-ions

• Addition of Silicon for improved energy density

• LTO Lithium Titanium Oxide for fast charging


LIB - Typical Electrolytes

• LiPF6 in organic solvent

• Additives for anode passivation, cathode protection, overcharge protection, safety, flame protection, lifetime,

reduction of gas formation…

• Ionic Liquids for flammability reduction

LIB - Separators• Polymer and/or ceramic

Cathode matrix

Anode matrix


Liquid electrolyte

Discharge

Charging power (kW)

Opportunity

charging

Battery strategy has to consider different applications

Two technology approaches to cover operation scenarios


Useable energy (kWh)

Depot

charging

• High charge power

• Medium

energy density

1st step

solid-state battery

• High energy

density

• Low

charge power

2nd step

+

Li ion

battery

(NMC)

Modular layout

• Established cell chemistry

• Applicable for opportunity and depot charging

• Cooling required

NMC Battery technology is based on modular concept

Evolution of modules for higher capacity in next step


• Anode: Graphite structure

• Cathode: NMC structure

(Nickel-Manganese-Cobalt)

• Ceramic separator & liquid electrolyte

cathode separator anode

liquid electrolyte

load

Li+cathode matrix

anode matrix discharging

New technology

• High energy density

• Inherently safe and sustainable cell chemistry

• Approximately 80kW charging power

• No cooling required

• Long lifetime perspective

Solid-state batteries are second technology path

Combination of high energy density and long lifetime perspective


• Anode: Pure Lithium metal

• Cathode: LFP

• No additional separator

• Solid-state polymer electrolyte

cathode anode

polymer electrolyte = separator

load

discharging

cathode matrix

cathode with Li

Li+ Li atom

Solid-state batteries enable maximum range with depot charging


Lithium-ion

NMC

Solid-state

battery

Useable energy [kWh] + + + +

Energy density [kg/kWh] + + + +

Lifetime [years] + + + +

Charging power + + + +

Flexible for depot and

opportunity charging

Depot charge

with maximum range

Daimler Buses

Definitions


• BoL Beginn of Life

• EoL End of Life

• SOH State of Health

How healthy is the HV Battery? How much has it aged?

• SOC State of charge

How much energy is in the HV Battery?

SOH =90% SOH =80%

Capacity HV Battery =100%

Capacity HV Battery = 80%

100% 40%

SOH =100%

Daimler Buses Developing the battery for an electric city bus | Daimler Buses | Frieda M. Davey Page 30

• DOD Depth of Discharge

How much energy per discharge is being extracted?

• SOC Range

In what range of SOC is the HV Battery being used?

• C – Rate

How fast is the HV Battery charged/discharged?

• Cyclability ( ≈ Lifetime)

How many times can the HV Battery be discharged of a DOD = X, temperature =Y, with a C-Rate =Z?

80% DOD 40% DOD

0%

100%

20%40%

SOC Range: 20% - 40% (DOD = 20%)

0%

100%

60%80% SOC Range: 60% - 80% (DOD = 20%)

Daimler Buses

Influencing factors on cyclelife


The lower the C-Rate…

…the higher the lifetime

C-Rate Lifetime

T = ideal T

T ≠ ideal T

Lifetime

Lifetime

Daimler Buses Developing the battery for an electric city bus | Daimler Buses | Frieda M. Davey Page 32

The smaller the DOD…

… the longer the lifetime

DOD Lifetime

The lower the SOC range…

… the higher the lifetime

SOC Range Lifetime

Relevant Parameters

Daimler Buses

Calendaric vs Cycling Aging


Calendaric aging

Aging fators:

• Storage temperature

• Storage SOC

Cyclic aging

Aging factors:

• Temperature

• C-Rate

• SOC Range

• DOD

Overall aging

• Depending on the power- and driving-profile, the HVB lifetime is more dependant on cyclic or calendaric

aging

• In general: Cars Driven little, parked a lot Calendaric Aging

City Bus Driven a lot, parked little Cyclic Aging

Daimler Buses Page 34

Cathode AnodeElectrolyte

Li+

e-

SE

I

SE

I

Electrolyte

Li+

e-

SE

I

SE

I

AnodeCathode

EoL:

• Side reactions at the interfaces. Part of the active material lost,

energy content decreases.

• By moving in and out of the electrode microstructure, the lithium ions

create micro cracks in the electrode material. The lithium ions have

increasing difficulty in diffusing, ionic resistance in the cell increases,

energy content decreases.

• The cracking of the electrodes leads to increase in volume in the cell

called „swelling“

BoL:

Cell aging


Daimler Buses

Cell formats


Pouchcell

Hardcase

CostsIntegrability

Density

Swelling

CyclabilityCooling

Manufacturing

Safety

Cylindrical

Daimler Buses Developing the battery for an electric city bus | Daimler Buses | Frieda M. Davey Seite 36

BEV Cells (Energy Cell)

• Higher capacity (more active material)

Thicker electrodes to host more Li+

Fewer rolls of electrodes+separator fit within the cell

Longer path for the Li+ to travel between cathode and anode

Higher internal resistance (reduced cyclability)

Meant for constant current over time

• Often bigger

• „Simple“ chemistry

Technical battery requirements for a bus:

• high cyclability (long lifetime of the battery on the bus) PHEV cell

• high capacity (high driving range of the bus) BEV cell

BEV cells fulfill certain of our requirements, PHEV cells fulfill others Compromise needed

PHEV vs. BEV cells

PHEV Cells (Power Cell)

• Lower capacity (less active material)

Thinner electrodes

More rolls of electrodes+separator fit within the cell

Shorter path for the Li+ to travel between cathode and anode

Lower internal resistance (improved cyclability)

Higher C-rates are possible

• Often smaller

• Improved and fined tuned chemistry

Cathode

Anode

Daimler Buses Developing the battery for an electric city bus | Daimler Buses | Frieda M. Davey Seite 37

PHEV vs. BEV

Example

- 300-400 km range (very high capacity)

- Only ca. 500 cycles (very low cyclability)

CAR: Assuming ca. 50 km/day 1 cycle per week 500 weeks ca. 9 years (calendaric aging not considered,

altough relevant)

BUS: A bus does 1 cycle per day 500 cycles 500 days Life < 1,5 years (!!!!)

Even if the bus is a BEV (battery electric vehicle), PHEV cells also need to be considered

to guarantee lifetime (cyclability)

Bus requirements ≠ Car requirements

Energy consumption

[kWh/km]

For evaluation of battery technology

driving cycle and temperature scenario need to be considered

10 12 14 16 18 20 22 24

Driving

Ventilation

Summer / air conditioning

Winter / electric heating

SORT1

cycle

SORT2

cycle

SORT3

cycle

Average vehicle speed [km/h]


+200%

Customer route coverage*

Coverage of entire customer operations

Range extender as effective completion of portfolio


Operation range [km]

Segment 1 Segment 2 Segment 3

Not covered by

depot charging

Potential solid-state battery >70%

Potential NMC battery appr. 50%

* sum of 1270 vehicle operations analysed

Potential for range extender

Solo & Articulated

Charging systems

Battery technologies

Fuel cell range extender

eMobility Consulting

Comprehensive approach

for electric mobility systems

The new Mercedes-Benz eCitaro

Fully embedded in a integrated eMobility system


Mercedes-Benz eCitaro

Coverage of relevant operational

requirements with a modular kit



Thank you


Documents

Product Engineering Daimler Buses High-Voltage Battery · Conclusion Good trade-off between range and charging power. Different operating concepts can be realized. Best suited for