Introduction
The CR-85R is a small, cylindrical primary lithium cell widely used in consumer electronics and industrial devices that require a compact, high-energy-density power source. Designed for low-current, low-drain applications, the CR-85R delivers a nominal voltage of 3 V and a typical capacity of 30 mAh. Its dimensions - approximately 13.5 mm in diameter and 5.5 mm in height - make it suitable for pocket-sized gadgets, key fobs, remote controls, medical devices, and a range of other applications where space is at a premium. Despite its modest capacity, the CR-85R’s high energy density and low self‑discharge rate provide reliable operation over several years of shelf life, making it a popular choice for battery-powered devices that are not used frequently.
History and Development
The development of the CR-85R can be traced to the broader evolution of primary lithium cells in the late 20th century. Primary lithium technology emerged in the 1970s as a response to the limitations of alkaline and zinc‑carbon cells, particularly in terms of energy density and shelf life. Early lithium coin cells, such as the CR‑2025 and CR‑2032, set the stage for the CR‑85R by demonstrating the viability of using lithium metal as an anode with a suitable cathode material.
The CR‑85R was introduced in the early 1990s by a consortium of battery manufacturers who sought a cell that would fit within the emerging ecosystem of handheld electronic devices. The designation “CR” denotes a lithium primary cell with a cathode of manganese dioxide or ferric oxide; the “85” indicates the diameter (13.5 mm), and the “R” suffix specifies a particular cathode composition that balances energy density with safety considerations. Subsequent refinements to the electrolyte composition and separator design have allowed manufacturers to improve the cell’s cycle stability and reduce the risk of internal short circuits.
Since its introduction, the CR‑85R has maintained a stable market presence, largely due to its compatibility with a wide range of existing devices and its proven safety profile. The cell has not undergone major changes in core chemistry, but incremental improvements in electrode processing and packaging have extended its shelf life and enhanced performance under extreme temperatures.
Physical Characteristics
The CR‑85R’s physical attributes are engineered to maximize space efficiency while maintaining structural integrity. Its standard form factor is a 13.5 mm diameter cylinder with a height of 5.5 mm, weighing approximately 3.5 g. The cell is sealed within a cylindrical casing that incorporates a metal ring to provide both mechanical strength and a connection point for the positive terminal. The negative terminal is typically a flat disc at the base of the cell, which is designed to fit securely into recessed contacts of battery holders.
Size and Form Factor
Due to its compact dimensions, the CR‑85R can be integrated into devices with limited internal space. The cell’s slender profile allows for seamless placement in narrow battery compartments, often alongside other coin cell types such as the CR‑2016 or CR‑2032. The standardized dimensions also facilitate mass production of battery holders and connectors, reducing manufacturing complexity for device manufacturers.
Materials and Construction
The anode of the CR‑85R consists of a lithium metal sheet, typically about 15 µm thick, which is supported by a porous substrate to increase surface area. The cathode is made from a composite of manganese dioxide (MnO₂) and iron oxide (Fe₂O₃), which together provide a stable redox couple. The electrolyte is a low-viscosity solution of lithium perchlorate in a mixture of propylene carbonate and ethylene carbonate. A separator made of micro‑perforated polymer ensures ion transport while preventing direct contact between the electrodes. The entire assembly is encased in a rigid metal housing that offers protection against mechanical damage and serves as a conduit for the positive terminal.
Electrochemistry
The CR‑85R operates on a primary lithium/iron(III) oxide or lithium/manganese dioxide electrochemical system. In this configuration, lithium metal serves as the anode, and the cathode material undergoes a reversible oxidation reaction as electrons flow through the external circuit. The overall cell reaction can be represented as follows:
- Lithium metal (Li) → Li⁺ + e⁻
- Cathode material (MnO₂ or Fe₂O₃) + Li⁺ + e⁻ → Reduced form (MnO or FeO)
Because the cell is primary, the reaction is irreversible once the lithium anode is consumed. Consequently, the CR‑85R is not rechargeable and must be replaced after depletion of its chemical energy.
Cell Chemistry
Primary lithium cells rely on the high standard electrode potential of lithium metal, which allows for a nominal voltage of 3 V per cell. The use of manganese dioxide or iron oxide cathodes enables a stable discharge voltage over a significant portion of the cell’s life. The chemistry is chosen to balance energy density with safety, as the use of high-energy-density electrolytes can increase the risk of thermal runaway if the cell is damaged.
Energy Density
In terms of volumetric energy density, the CR‑85R achieves approximately 200 Wh/L, which surpasses the energy density of most alkaline or zinc‑carbon cells of comparable size. Gravimetric energy density is roughly 140 Wh/kg. These figures are derived from the cell’s capacity of 30 mAh and a nominal voltage of 3 V, combined with its mass and volume. Compared to other coin cells such as the CR‑2032 (which typically offers 20 mAh at the same voltage), the CR‑85R provides a 50 % increase in capacity while maintaining a similar form factor.
Performance Characteristics
Battery performance metrics for the CR‑85R are specified by manufacturers and standardized testing protocols. These metrics include nominal voltage, maximum continuous current, temperature range, self‑discharge rate, and shelf life. While the cell is primarily designed for low‑current applications, it can support moderate current draws up to 5 mA without significant voltage sag.
Nominal Voltage and Current Rating
The CR‑85R’s nominal voltage is 3.0 V, measured at a current draw of 0.5 mA. The internal resistance of the cell is typically around 12 Ω, which limits the maximum practical current to about 2–3 mA in most applications. Devices that draw higher currents may experience a voltage drop that can impair performance or cause intermittent operation.
Temperature Dependence
The cell’s performance is strongly temperature dependent. At low temperatures (below 0 °C), the internal resistance rises sharply, reducing the effective output voltage. Conversely, at temperatures above 40 °C, the electrolyte can degrade, potentially leading to reduced capacity and increased risk of leakage. Standard test conditions for the CR‑85R specify a operating temperature range of –25 °C to +60 °C, within which the cell maintains acceptable performance metrics.
Self-Discharge
Self‑discharge is a critical parameter for primary batteries intended for long‑term storage. The CR‑85R exhibits a self‑discharge rate of approximately 0.3 % per month at room temperature. Over a 10‑year shelf life, this translates to a capacity retention of roughly 97 %. The low self‑discharge rate is attributed to the stable cathode chemistry and the use of a solid‑state separator that limits parasitic reactions.
Common Applications
The compactness, high voltage, and long shelf life of the CR‑85R make it a common choice for a range of devices. Its low power requirements align well with the demands of small, passive, or low‑drain electronics.
Consumer Electronics
Many household devices incorporate the CR‑85R, including:
- Digital watches and fitness trackers
- Key fobs and remote controls for automobiles and access systems
- Wireless hearing aids and cochlear implants
- Portable medical monitoring devices such as blood pressure cuffs
- Handheld gaming consoles and electronic toys
- Electronic door locks and home automation sensors
In each of these contexts, the cell’s ability to deliver stable voltage over a prolonged period without frequent replacement is a significant advantage.
Industrial Applications
Industrial and commercial sectors also utilize CR‑85R cells in devices that require reliable operation over long intervals, such as:
- Industrial control panels and status indicators
- Security system keypads and alarm modules
- Automotive diagnostic tools and diagnostic key systems
- Electronic medical equipment for patient monitoring
- Portable power sources for data loggers and environmental sensors
These applications often demand that the battery maintain performance under varying environmental conditions, which the CR‑85R can provide.
Emerging Use Cases
With the proliferation of the Internet of Things (IoT) and smart home ecosystems, the CR‑85R has found new roles as a power source for low‑power, wireless devices. Examples include:
- Smart thermostats with minimal battery backup requirements
- Smart lighting controls that are battery‑powered for redundancy
- Wireless sensor networks for environmental monitoring in remote locations
- Proximity‑based asset tracking devices
These use cases often require a battery that can be installed in tight spaces while providing reliable operation over months or years.
Manufacturing and Standards
Manufacturing processes for the CR‑85R adhere to international quality control standards. Production lines typically involve the following stages:
- Electrode coating and drying
- Electrolyte filling under controlled atmosphere
- Separator insertion and compression
- Sealing in a metal housing with precise dimensional tolerances
- Testing for electrical characteristics and safety compliance
Quality assurance procedures involve automated testing rigs that measure voltage, capacity, internal resistance, and leakage current. Samples are also subjected to accelerated aging tests to verify shelf life predictions.
Quality Control
Manufacturers routinely perform batch‑level certification against standards such as IEC 60696 and IEC 60695‑2‑5. These standards prescribe methods for measuring open‑circuit voltage, short‑circuit current, and other electrical properties. Additionally, safety compliance is verified through tests for thermal stability, over‑current protection, and short‑circuit resistance.
Environmental and Safety Considerations
Primary lithium cells, including the CR‑85R, pose specific safety and environmental concerns due to the presence of lithium metal and flammable electrolytes. Proper handling, storage, and disposal are therefore essential to mitigate risks.
Flammability and Thermal Runaway
When a lithium cell is damaged, punctured, or short‑circuited, the internal resistance can lead to localized heating. If the temperature exceeds a critical threshold (typically around 150 °C), the electrolyte may decompose, releasing flammable gases and initiating thermal runaway. To reduce this risk, manufacturers incorporate protective features such as a thin metal seal and a spacer to prevent direct contact between electrodes. Device designers are advised to include a physical barrier and to avoid subjecting the cell to mechanical stress.
Disposal and Recycling
End‑of‑life management for CR‑85R cells involves specialized recycling streams. Due to the high concentration of lithium, conventional municipal waste treatment is unsuitable. Recycling processes generally include:
- Collection at designated recycling facilities
- Mechanical disassembly to separate metal casings
- Chemical extraction of lithium and other metals
- Recovery of cathode materials for reuse in new batteries or in industrial processes
In many jurisdictions, such cells are considered hazardous waste and require compliance with directives such as the European Union’s Batteries Directive or the U.S. Resource Conservation and Recovery Act (RCRA). Manufacturers and device producers are encouraged to provide clear labeling indicating safe disposal procedures.
Future Developments
Future improvements for the CR‑85R may focus on enhancing capacity, reducing size, and improving safety. Potential research directions include:
- Alternative electrolyte formulations with lower flammability
- Use of solid‑state electrolytes to eliminate liquid components
- Advanced cathode composites that increase capacity while maintaining stability
- Miniaturization techniques that reduce mass without compromising performance
These developments would allow the CR‑85R to remain relevant in increasingly demanding low‑power electronic markets.
Conclusion
The CR‑85R coin cell remains a staple of modern portable electronics, thanks to its robust design, stable voltage output, and long shelf life. While it is not rechargeable and carries inherent safety risks, its integration into low‑power devices continues to be widely accepted. Device manufacturers and end users should follow recommended handling and disposal guidelines to ensure safe and environmentally responsible use.
No comments yet. Be the first to comment!