2012 Mitsubishi i main drive lithium-ion battery

Lithium-Ion Batteries – Proven Safety, Reliability and Storage Capacity
With over four decades of experience in designing and developing 100% battery-powered vehicles (BEV), Mitsubishi Motors is a global leader in the exciting new automotive medium of production electric vehicles (EV). And with the introduction of the all-new 2012 Mitsubishi i, the North American consumer will be able to make a significant personal contribution to improving the environment with the purchase of the most affordably priced EV available in the marketplace to date.

The 2012 Mitsubishi i is likely the first of many production vehicles to come from the Japanese auto manufacturer that will utilize the exceptionally efficient Mitsubishi innovative Electric Vehicle (MiEV) battery-powered electric vehicle technology that will allow consumers to enjoy the numerous benefits that EVs and plug-in hybrid electric vehicles PHEVs have to offer. These include vastly reduced operating costs (electricity costs less than fuel, lower routine maintenance expenditures) and greenhouse gas emissions, an ever-expanding private and public recharging infrastructure and, in many areas, the added convenience of access by an individual driver to a freeway’s high occupancy vehicle (HOV) “car pool” lane, to name but a few.

Main Drive Lithium-ion Battery Placement
Mitsubishi engineers cleverly positioned the battery pack of the Mitsubishi i beneath the vehicle sub-floor for a number of reasons: 

Packaging
Placing the lithium ion battery pack in the floor of the 2012 Mitsubishi i provides numerous benefits including:

• Maximizing interior volume to the benefit of the driver, passengers and cargo.
• Improving the center of gravity for stable handling performance.
• All electrical components are put under the floor to keep passengers away from high voltage.

Safety

Structurally-Sound Battery Encasement
Mitsubishi Motors has designed the all-new 100% battery-powered Mitsubishi i electric vehicle so that damage to its lithium-ion battery pack is minimized in the event of an accident, thus ensuring maximum protection to the driver and occupants.

The battery pack is located beneath the vehicle's interior floor (sub-floor) and the chassis (body frame) inside a specially-designed stainless-steel protective battery case. This design not only helps to protect the battery pack in an accident but also minimizes penetration of objects/debris that can be picked up from the road surface while driving. Additionally, this stout support structure also aids the vehicle's structural rigidity as it is bolted directly onto the chassis.

Critical components that form a protective barrier to the main drive lithium-ion battery pack include the battery protector (a thick skid plate located aft of the front wheels and in front of the battery pack), the undercover (a protective covering over the entire battery pack) and the supporting frame system (several fortified braces that rests between the battery pack and the undercover that hold the latter item in place).

The lithium-ion battery pack encasement structure is completely waterproof.

Please see the "Safety" section of this press kit to learn more about the wide array of occupant and pedestrian safety technologies that are standard equipment on all 2012 Mitsubishi i models.

Advanced Lithium-Ion Batteries
A key component that makes an all-electric production vehicle possible today is the advancement of battery technology – an area where the Mitsubishi Motors Corporation is a world leader, having researched, designed and developed 100% battery electric vehicles (BEV) for more than 40 years.   

The lithium-ion batteries used for electrical energy storage in today’s automobiles may in many respects be similar to the batteries found in popular consumer products like cell phones and laptop computers, but the specialized battery cells/battery packs utilized by Mitsubishi Motors for an automotive application are vastly superior in an area of critical importance – safety.

Thanks to its decades of experience in working with battery-powered electric vehicles Mitsubishi Motors has established an extensive range of tests and processes to ensure the highest degree of both performance and safety from its lithium-ion batteries:

Safety technologies found in each individual battery cell

• Special positive electrode material
• Heat-resistant insulating resin
• Low-pressure operation safety valve
• Thick separator
• Very strong metal casing

Safety technologies found in the battery pack

• Electric leakage sensor
• Electric current sensor
• Main quick-charging current cut off
• Service plug
• Fuse

Effect of temperature on lithium-ion batteries:

Cold weather

The major effect that cold weather has on lithium-ion batteries is that the speed with which the batteries are recharged is slowed when the temperature is below 32° Fahrenheit (0°Celsius). In those geographic regions where temperatures fall below freezing, the Mitsubishi i can be equipped with an optional Cold Zone package which includes a battery warming system ($150; also includes heated side mirrors).

Hot weather

The major effect that hot temperatures have on lithium-ion ion batteries is that, if the batteries are exposed to extreme high temperatures for extended periods of time the lithium-ion batteries will experience degradation.

Mitsubishi estimates that after 5 years, the capacity of the Main Drive Lithium-ion battery will be approximately 80% of its original capacity. After 10 years, the capacity should be approximately 70%. Other factors that can adversely affect battery capacity over time include frequent driving using aggressive acceleration/deceleration, repeated frequent use of the quick charger, and vehicle operation/storage in extreme temperature environments.

Battery Charging
The 16 kWh lithium-ion battery pack found on the 2012 Mitsubishi i can be charged by three different methods - a 120 V Level 1 charger that utilizes a portable charging unit that plugs into a standard electrical outlet (estimated charge time – 22 hours), a faster 240 V Level 2 EVSE charging system that is the recommended method by Mitsubishi Motors (estimated charge time – 7 hours; this professionally-installed charging system is available at Best Buy retailers), and the ultra-fast Level 3 DC quick charging system that will be available at public electric vehicle charging stations.

The fastest Level 3 charging capability is included with the Premium Package that is available with the upgrade Mitsubishi i SE model.

Quick-Charging Battery System

An especially convenient way to charge the 16 kWh battery pack of the 2012 Mitsubishi i is via the optional CHAdeMO Level 3 DC quick charging port. Available at many public electric vehicle charging stations (including the solar-powered EV charging station located at Mitsubishi Motors North America, Inc. headquarters in Cypress, California), this is the fastest method to recharge the vehicle's lithium-ion battery pack - a very low battery level can be replenished to 80% full in less than 30 minutes.

The 2012 Mitsubishi i makes use of the CHAdeMO protocol for high-speed EV charging, a standard that has proven popular in both Mitsubishi’s native country and across Europe.

Battery Temperature Conditioning System
The 2012 Mitsubishi i includes a battery temperature conditioning system to ensure optimal performance, reliability and longevity of the advanced lithium-ion battery pack.

This system performs two critical functions: to cool the battery pack during Level 3 quick charging so that it does not get excessively hot, and to warm up the battery pack when it is undergoing Level I or Level II charging in case the battery temperature is too low.

This is accomplished by a forced air ventilation system that makes use of the HVAC blower forces to flow heated or cooled air around the battery pack via a special battery ventilation fan.

The battery temperature conditioning system is composed of the following components:

• HVAC

Heating, ventilating and air-conditioning system

• Switching damper

Redirecting heated/cooled air from the passenger compartment to the battery pack

• Floor duct

Ducting connecting the HVAC system and battery pack

• Air duct

Specialized ducting for air distribution to battery pack

• Battery ventilation fan

To exhaust the conditioned air that circulates around the battery pack

Battery Cooling System
When the vehicle’s ECU detects that a Level 3 DC quick charging connector has been plugged into the vehicle, it then determines whether the battery pack requires cooling based on battery temperature information from the BMU (Battery Management Unit). If it deems that cooling is necessary, the ECU then signals the compressor heater control unit that controls the compressor, A/C control unit and the HVAC system while communicating simultaneously with the battery management unit (BMU) to engage the battery ventilation fan.

The cooling system only becomes operational when it detects that the battery temperature is above 68 °Fahrenheit (20° Celsius); in this initial phase the HVAC blower fan and the battery ventilation fan are engaged. If the ECU determines that the battery temperature exceeds 86° Fahrenheit (30° Celsius), then the HVAC blower fan and the battery ventilation fan are supplemented by the air conditioner.

Battery Warming System
When the vehicle's ECU determines that a "regular" (Level 1 or Level 2) charging connectors plugged into the Mitsubishi i, it then determines whether or not battery heating is necessary based on battery temperature information from the battery management unit (BMU). If the system deems battery heating necessary, it then starts the compressor heater control unit which controls the heater, the A/C control unit and the HVAC system while concurrently telling the BMU to turn on the battery ventilation fan.

Normal Mode
The battery warming system operates when the system determines that the battery temperature range is within -20° and -13° Fahrenheit (-29° to -25° Celsius); the heating system does not engage when the battery temperature is determined to be less than -22° Fahrenheit (-30° Celsius). Of note, the battery warming system will not activate when the lithium-ion batteries state of charge (SOC) is less than 40%.

Battery warming ceases when the battery temperature reaches -4° Fahrenheit (-20° Celsius) or if the state of charge (SOC) is calculated to be under 10%. When battery charging ends the ECU enters into a sleep mode, waking six hours later to check the temperature of the battery pack; heating of the battery will once again commence if necessary.

MiEV Remote Mode
If the owner of a Mitsubishi i has programmed the vehicle to begin and end charging the battery pack at specific intervals, then the battery heating system functions in a similar manner to that of the "Normal” mode, save for the battery warming system turning off at the same time as when the owner has programmed the battery charging to end.

MiEV OS - Mitsubishi innovative Electric Vehicle Operating System
With over four decades of experience in designing and developing 100% battery electric vehicles (BEV), Mitsubishi Motors has developed the new Mitsubishi i from an incredibly comprehensive database of electric vehicle know-how. Playing a leading role in the North American-spec version of the company's latest EV model is the remarkable new Mitsubishi innovative Electric Vehicle operating system, MiEV OS.

The MiEV OS allows the advanced integration of optimum control of the critical electric motor/lithium-ion battery matrix that powers this next-generation electric vehicle in an exceptionally safe, comfortable and energy-efficient manner.

The MiEV OS oversees and monitors the function of these vital components:

• Electric Vehicle motor
• Main Drive Lithium-ion battery pack
• Battery Management Unit (BMU)
• Inverter – Motor Control Unit
• On-board vehicle charger & DC/DC converter
• Driver inputs (throttle, brake, gear selection, etc.)
• Safety systems (traction control, ABS, air bags, etc.)
• Electric motor unit cooling system

The management of all of the aforementioned components are overseen by the vehicle integration controller (EV-ECU). The EV-ECU utilizes information from each of these components to control a wide range of systems including:

• Battery management system
• High voltage control system
• Cruising range estimation
• Traction control
• Smooth start control
• Battery energy level estimation
• Regenerative brake control
• Power save control

Battery Management System
The Battery Management System consists of the battery management unit (BMU), cell monitoring units (CMU) that monitor the state of each individual lithium-ion battery cells (one CMU per battery cell; a total of 88 cells in each vehicle battery pack), a leakage sensor to determine if there is any leakage from the high voltage system and an electric current monitor to constantly watch over the battery pack’s amperage. 

The battery management system continuously safeguards the state of the vehicle’s batteries at all times.

High Voltage Control System
If the 2012 Mitsubishi i should be in a collision, the main drive lithium-ion battery pack fails or if failsafe systems detect any battery leakage, the High Voltage Control System instantly triggers the high voltage circuit to shut off from the main battery to help protect the driver, vehicle occupants and/or rescue personnel.

utilized in the air bag, the High Voltage Control System deactivates the circuitry. As a special precaution, Mitsubishi engineers have added a specialized supplemental G-sensor that automatically shuts off the high voltage circuit should the impact level in the collision be so great that it damages the High Voltage Control System.

Additionally, if the on-board diagnostics receives any information that it deems may lead to a serious failure of the vehicle’s operation, the High Voltage Control System will leap into action and perform a high voltage system shut off.

Cruising Range Estimation
The cruising range of the Mitsubishi i is estimated continuously by determining electric power consumption and the capacity level of the battery. The system estimates the average electrical power consumption from data supplied by the battery management unit (BMU) and the inverter-Motor Control Unit while simultaneously factoring in information relayed to it from the HVAC system and the onboard charger. The cruising range control unit takes this information, along with the actual switchgear positions over the air conditioning/heater controls that have been selected by either the driver or the front passenger, to determine the estimated driving range of the vehicle.

Thanks to the comprehensive tabulations and data inputs that take place by the cruising range control and the Mitsubishi innovative Electric Vehicle Operating System, Mitsubishi i owners can rely on a real-time cruising range estimation at any given moment while operating their new environmentally-friendly and efficient EV.

Traction Control
In a "conventional" vehicle (one with an internal combustion engine), a traction control system helps to improve tractability in poor weather or in slippery road conditions as well as improving vehicle stability under acceleration. But the traction control on the 2012 Mitsubishi i takes traction control one step further by not only controlling vehicle stability under braking but at the same time maximizing the amount of energy produced and fed back into the Main Drive Lithium-ion battery pack by the regenerative braking system.

Smooth Start Control
Due to the quick response of electric motor torque, jerky vehicle behavior generally occurs when accelerating from a standstill due to the instantaneous peak torque available from an electric motor - but not with the Mitsubishi i. The Smooth Start Control technology developed on the Mitsubishi i provides an ultra-smooth launch every time as it effectively restrains electric motor torque at the start  which helps to reduce annoying drivetrain vibration. The result is smooth and quick acceleration.

Battery Energy Level Estimation
To help ameliorate consumer concerns about “range awareness” with ownership of an electric vehicle, Mitsubishi engineers have developed a Battery Energy Level Estimation system for the 2012 Mitsubishi i so that drivers will know precisely how far they'll be able to drive at any given time while operating the vehicle.

The Battery Energy Level Estimation system takes a variety of technical criteria into account including an estimation of the state of charge (SOC) and energy capacity of the battery pack, along with battery current and cell voltage information as well as driving conditions.

The system also looks at an historical behavior to examine usage and charging patterns to intelligently make an ongoing estimation of the battery pack’s capacity to provide the most accurate picture of how much energy the main drive lithium-ion battery is actually capable of storing.

The end result is a highly accurate visual display of the vehicle’s estimated battery energy level for the driver to see on the "energy" gauge on the instrument cluster.

Regenerative Brake Control
The Regenerative Brake Control system’s goal is to provide the maximum amount of regenerative energy back into the lithium-ion battery pack in the most controlled and efficient manner.

The system calculates the torque level from the electric motor based on the shift lever position (D, Eco, or B), and the accelerator and brake pedal positions. Data from the anti-lock braking system (ABS), the battery management unit (BMU) and the inverter-Motor Control Unit (MCU) are also factored into the equation to help optimize torque levels.

The driver can see a visual metric while the Regenerative Brake Control system is at work simply by glancing at the "Charge/Eco" needle gauge at the upper left hand section of the speedometer readout. The needle will drift down into "Charge" under braking and regenerate energy into the battery pack while the needle will move up into "Eco" when discharging power under acceleration.

Power Save Control
The Power Save Control system makes a significant contribution to reducing electrical energy consumption - with the driver hardly ever noticing it is doing so.

Like the Regenerative Brake Control system, Power Save Control takes in driver input data including accelerator and brake pedal positioning, along with air conditioning or heater settings, as well as information from the inverter-Motor Control Unit, the vehicle's Main Drive Lithium-ion battery capacity level and torque production from the electric motor to determine whether or not the car should go into a power saving mode by automatically reducing the output from the HVAC system and/or slightly restricting available torque levels from the electric motor.

The Power Save Control system operates from the conventional "D" drive setting gear selection on the shift gate.