Metal finishing requirements in the battery industry

Anode

lead tab

Cathode

current collector

Anode

current collector

Corrosion inhibition & Ni plating

Al corrosion & adhesion treatments

Cu plating, corrosion & adhesion

Connectors

& bus bars

Silver plating, Nickel Plating, Electroless Nickel

PCB

Cu plating, adhesion & final finishes

https://www.technologyreview.com/2012/06/19/185373/lithium-ion-battery/ Copyright © 2021, All rights reserved MIT Technology Review; www.technologyreview.com

• Connectors for Powertrain
• Battery Charger
• Bus Bars to Connect Cells

​

• Anode Lead Tabs

• Current Collectors (Cu)

• Current Collectors (AL)
• Current Collectors (Cu)

​

• Current Collectors (Al)
• Current Collectors (Cu)
• Neg. Lead Tab

​

• Low contact resistivity
• Hard Silver for wear/fretting resistance

​

• Corrosion protection
• To enable stable and specific clamping forces (CoF)
• Improving contact corrosion

• High perfomance Cu Plating Electrolytes
• High speed, low stress and pin hole free

​

• Adhesion Improvement of current collector to active materials/binders
• For new active materials with increased expansion

• Cr(VI) free anti-tarnish layer
• Improved corrosion protection for hydrofluoric acid (HF) with passivation layer

• Silver plating
• Nickel sulphamate HS
• Corrosion Inhibitors for Silver

• High Speed Nickel
• Satin Nickel

• High Speed Copper

• Adhesion Promotors

• Corrosion Inhibitors
• Conversion Coatings

Module part

Purpose

Process

Metal Finishing Requirements in the EV Industry

Fasteners

Battery Junction Box

Corrosion protection

• Zn and ZnX plating, Zinc flakes

Busbars, Connectors, PCB

• Silver plating
• Al & Cu treatments
• PCB processes*

Housing

Pretreatment, Paint support

• Al treatment, paint pretreatment

Battery Management

Heat sinks, connectors, BMS (Master ECU, Battery Junction Box, Cell Module Unit, Current Sensor), Bus bars (copper & aluminum), Lead frames, QFNs

• PCB processes*
• Plating on plastics, pretreatment

*Desmear & metallization, Cu plating,

adhesion promoter, ENIG, Immersion Tin

Cell

Management Controller

Lower housing shell

Cell

Battery Management Controller

Upper

housing shell

Battery junction box

Fasteners

• Battery management system
• Cu or Al heat sinks
• PCB and semiconductors
• Lead frames, press fit, QFNs

​

• Fasteners for joints at the contact of metal- and non-metal material mix
• Holders, fixtures

• Al bus bars
• Battery terminal clamps
• Current collectors Cu
• Al and Cu heat sinks for IGBT

• Battery cell housing
• Modul housing

​

• Connectors for powertrain 
• Battery charger
• Busbars to connect cells

​

• Light-weight plastic housing
• EMI shielding
• Heat sink corrosion protection
• ML-PCBs / heat management, corrosion resistant SF, thick copper, AP
• QFNs / 3-dimensional solder joint

• Corrosion protection
• To enable stable and specific clamping forces (CoF)
• Improving contact corrosion

• Corrosion protection
• Wear resistance
• Solderability

• Corrosion protection
• Preparation for e-coating
• Al anodizing

• Low contact resistivity at high corrosion resistance
• Hard silver for wear / fretting resistance

• Plating on plastic
• Nickel Iron
• PCB Plating

• Zn, ZnNi, SnZn
• Post-treatment (passivates, sealers, topcoats)

• Aluminum pre-treatment
• Electroless nickel plating
• Immersion tin plating

• Zn, ZnNi plating
• Al cleaning and passivation
• Electroless nickel plating

• Corrosion Inhibitor
• Nickel Sulphamate HS
• Hard Silver Plating

Module part

Purpose

Process

Fasteners

Shafts

Corrosion protection

• Zn and ZnX plating, Zinc flakes

Shafts to wheels

• EN plating
• Hard Chrome Plating

Inverter, converter

• Driver for e-engine
• Semiconductors/IGBT, diodes, sensors, etc.
• PCBs
• Bus bars (copper & aluminum)
• Lead frames, press fit pins, QFNs

Connectors

HV & high current connectors

• Surface treatments

​

Housing

Housing, heat sinks, connectors

• Plating on plastics, pretreatment
• Zi, ZnNi plating
• Al cleaning & passivation
• Phosphates
• EN plating

​

​

Metal Finishing Requirements in the EV Industry

C

B

• Semiconductors / IGBT, Diodes, Sensors, etc.
• PCBs
• Bus bars (copper & aluminum)
• Lead frames, press fit, QFNs

• Fasteners for joints at the contact of metal- and non-metal material mix
• Holders, fixtures

• Shafts
• Scroll compressor parts
• Condenser plates

​

• E-engine parts
• Differential and motor housing

• Power connectors
• Harnesses

• IGBT / double sided copper plating
• Diodes / adhesion & plating on resins
• ML-PCBs / embedding components, heat management, adhesion and corrosion resistance

• Corrosion protection
• Stable and specific clamping forces (CoF)
• Improving contact corrosion

• Wear reduction
• Durability

• Corrosion protection
• Preparation for e-coating
• Al anodizing

• Low contact resistivity
• Hard-silver for wear/fretting� resistance
• High temperature stable � physical properties 

• PCB Plating
• Silver Plating

• Zn, ZnNi, SnZn
• Post-treatment (passivates, sealers, topcoats)

• Electroless nickel plating

• Zn, ZnNi plating
• Al cleaning and passivation
• Electroless nickel plating

• Corrosion Inhibitor
• Non-Cyanide Silver
• Hard Silver

Module

part

Purpose

Process

Base material: aluminum

Conversion coating:

10–100 µm

Complete coating process

• Degrease to remove organic contaminants
• Surface preparation to remove inorganics oxides
• Conversion coating for superior adhesion and corrosion performance

Pretreatment of Al housing ensures superior adhesion of paint and resistance to corrosion

For defective housings due to paint rejects, complete removal of the paint is required prior to re-paint

Cleaning

Phosphating

Adhesion Promotion

Passivation

Base Al substrate (no coating)

Al with              

Zr coating

Passivation

Cleaning/Desmut

Paint removal 

Phosphate- Paint pretreatment

Organic coating/ Paint

100 - 300 µm

Al bus bar plating

For low resistivity and contact resistance

IGBT heat sink

Electroless nickel process for corrosion protection, solderability and uniform thickness distribution

Problem

Solution

Why

• Current process is using Ni/Cr coating applied via PVD, cost-effective alternative
• Reduce heat generation

Processes:

• Low P electroless nickel
• Silver as topcoat layer for best electrical conductivity (2 - 3 μm/min.) 
• Anti-tarnishes

• To provide low resistivity and low contact resistance coatings
• Provide full coverage and good corrosion protection

• Achieving satisfactory adhesion on the inside brazed area
• Good thickness distribution inside the part

• Pre-treatment for satisfactory cleaning of the brazed areas
• Electroless Nickel (MP/HP)
• Anti-Tarnishes

​

• The inside of the heat sink, which is water cooled, is plated with electroless nickel:
• Thickness distribution
• Corrosion protection

vs

ICE

EV

Peugeot 208 e GT 2020

Peugeot 208 1.2 Puretech GT Line 2019

~ 2000 pieces of fasteners

• Fasteners which are directly involved in current flow
• Fasteners which are chosen for new design reasons
• Fasteners which are used for weight reduction (Al fasteners)
• Fasteners with new requirements
• Contact corrosion (mix of different metals)
• Assembling in new materials like copper bus bars

It is important to have defined requirements �and test methods

For classical bolt connections the focus is on:

“Thick and alternating metal layers” is the sweet spot of electroplating

Low frequency

electrical field

Low frequency

magnetic field

High conductive material

Thick material – compared to ‘Skin Depth’

+

Electroplating

Automotive in-vehicle infotainment (IVI) system - Infineon Technologies

Vibrational stability

High frequency applications

High contact normal force

High currents

Tin

42� $/kg

Silver

750 �$/kg

Gold

58 �k$/kg

Non power train system in e-vehicles such as infotainment and ADAS are still relying on standard specifications 🡪 standard connectors

Power train & Battery connections

Powertrain

E-vehicle

Application

Highly conductive, corrosion resistant and temperature stable surface finishes

Processes

Pre-treatment, nickel, hard silver, anti-tarnishes

Bus bars

Connectors

• Aluminum
• Cu and Cu alloys
• Steel

​

Pretreatment

• High speed pure nickel
• High P (12%) nickel

Nickel plating

• Hard silver
• Cyanide free (R&B)
• High speed plating
• Sustainability or Green Tin products.

Silver and tin plating

• For silver, tin and Copper
• To protect from heat and humidity

Anti-tarnishes

The metal stack of choice

• Nickel as a barrier coat for corrosion and wear resistance
• Hard silver for wear resistance
• Low contact resistance
• Anti-tarnishes for improved conductivity

​

A stack of nickel 

Hard silver and anti-tarnish for bus bars and connectors

Nickel Sulphamate 

Hard Silver

Anti Tarnish 

Plating processes

Nickel 2 µm

High speed Tin� > 2µm

Anti Tarnish <1 nm

The metal stack of choice

• Nickel as a barrier coat for corrosion and wear resistance
• Sustainable Sn additives processes are commercially available
• No CMR, BPA, NPE...containing additives
• Anti-tarnishes to withstand heat and humidity

Bus bars

cell or module connections

Alternative to 

hard silver on bus bars 

Tin plating: 

Low contact resistance under high pressure (e.g. bolted bus bar connections) 

Nickel Sulphamate 

High Speed Tin

Anti Tarnish

Plating processes

Anti-tarnish

High speed plating

Low contact resistance for bolted connections

The metal stack of choice

• Hard EN (low Phos)
• Increased wear resistance & corrosion protection
• Excellent barrier layer
• Low contact resistance produced by silver
• Anti-tarnish for increased conductivity
• Design Freedoms – Uniform Thickness

​

​

​

A stack including electroless nickel is ideal for application where uniform thickness, high wear resistance and increased corrosion protection is required for bus bars and connectors

Electroless Nickel (Low P)  

Hard Silver

Anti Tarnish

Plating processes