When a sheet of electrolytic copper with a uniform rose-gold luster is presented before your eyes, its
value extends far beyond its captivating appearance. This seemingly simple metal is a masterpiece of
precise chemical and physical balance. Understanding the composition of electrolytic copper is not only
the core of quality assessment but also the key to understanding why it has become an indispensable
material in the fields of power, electronics, and high-end manufacturing.
Core: Copper Element with Purity as the Top Priority
Undoubtedly, copper (Cu) is the absolute main component of electrolytic copper, and its content is
the gold standard for measuring quality grades. For the highest grade of electrolytic copper (such as
that meeting LME registered brand standards or national standards for high-purity cathode copper
Cu-CATH-1), the copper content requirement reaches an astonishing 99.9935% or higher. This means
that the total weight of all impurities in each ton of product is strictly limited to 65 grams or less. This
near-perfect purity is the core distinguishing feature of electrolytic copper compared to fire-refined
copper, and it is the fundamental guarantee of its exceptional conductivity (approaching theoretical
values), excellent thermal conductivity, outstanding ductility, and processing performance.
The delicate balancer: inevitable impurity elements
Despite its extremely high purity, the presence and concentration of trace impurity elements (typically
measured in parts per million (ppm) or even parts per billion (ppb)) play a decisive role in the performance
and applications of electrolytic copper. These elements are not all “harmful”; their impact depends on
their type, concentration, form of existence, and distribution within the copper matrix.
Based on their impact on performance, impurity elements can
be broadly categorized into several groups:
Phosphorus (P), Arsenic (As), Antimony (Sb), and Bismuth (Bi): These elements are highly detrimental. Even
at extremely low concentrations (a few ppm), they strongly scatter conduction electrons, significantly reducing
copper's electrical conductivity (IACS% conductivity). Furthermore, they tend to segregate at grain boundaries,
triggering “hot brittleness” or “cold brittleness,” making the material prone to cracking during subsequent
rolling or drawing processes. Grade A electrolytic copper enforces a near “zero-tolerance” policy for such impurities.
Iron (Fe), nickel (Ni), tin (Sn), zinc (Zn): These elements also reduce conductivity, but their impact is relatively
weaker than the previous category. Their presence may also affect the material's mechanical properties and
weldability. Their content has explicit upper limits specified in standards.
The “destroyers” of processing performance and surface quality:
Sulfur (S), oxygen (O), selenium (Se), and tellurium (Te): Oxygen content must be strictly controlled (typically
<10 ppm), as excessive levels increase the risk of “hydrogen embrittlement” (defects are prone to form in
reducing atmospheres). Elements such as sulfur, selenium, and tellurium tend to form brittle compounds
with copper or other metals, impairing hot working properties and potentially causing defects on the
material surface or affecting coating quality.
High-value “inert” presence - precious metals:
Silver (Ag), gold (Au), platinum group metals (Pt, Pd, etc.): These elements are highly valuable in themselves,
but when present as impurities in electrolytic copper, they are nearly insoluble in the copper matrix and typically
exist as small particles or concentrated at grain boundaries. Although their impact on conductivity is relatively
minor (silver even slightly enhances it), their presence reflects the origin of the raw materials. More importantly,
their presence increases material hardness, which may have adverse effects on certain ultra-fine wires or special
applications with extremely high requirements. Their primary value lies in recycling—they are enriched in
anode sludge.
Physical form: Microstructure determines macro performance
The performance of electrolytic copper is not only determined by its chemical composition but also by its
physical structure—the morphology, size, orientation of microcrystals, as well as the distribution of pores
and inclusions within—which is the essence of the electrolytic refining process control.
Crystalline morphology: The ideal electrolytic copper deposit should have a dense, uniform, equiaxed
fine-grained structure. This depends on:
Optimized electrolytic parameters: Appropriate current density, electrolyte temperature, circulation rate,
and the use of additives (such as gelatin, thiourea, and chloride ions) can effectively suppress dendritic
crystallization (which tends to produce pores and impurity inclusions) or sponge-like deposition (which is
porous and low in strength), promoting the formation of a smooth, dense deposition layer.
Clean substrate: The surface smoothness and flatness of the cathode starting plate or mother plate directly
affect the quality of the initial deposition layer.
Surface and internal defects:
Surface: Defects such as nodules, pits, cracks, foreign material adhesion, and oxidation discoloration should
be avoided. These defects not only affect appearance but may also serve as fracture sources during subsequent
processing (e.g., rolling, drawing) or impact the surface quality of the final product.
Internal: Pores, shrinkage cavities (primarily associated with cast anode plates, but stress in the electrolytic
deposition layer itself or trapped gases may also cause them), and non-metallic inclusions (such as unremoved
anode sludge particles or contaminants introduced by the purification system) can significantly reduce the
material's density, mechanical properties, and electrical conductivity uniformity.
“Liquid Foundation”: The Contribution and Challenges of Electrolyte
The electrolyte (primarily composed of copper sulfate and sulfuric acid) not only serves as a medium for
copper ion migration but its own purity also indirectly influences the composition of the final cathode copper:
Accumulation of impurity ions: During anode dissolution, impurity ions (such as Ni²⁺, Fe²⁺, As³⁺, Sb³⁺, Bi³⁺, etc.)
entering the solution will continuously accumulate if not controlled and removed. Although copper is preferentially
deposited at the cathode, extremely high impurity concentrations increase the risk of impurity co-deposition,
especially in high current density areas or when electrolyte circulation is poor. Therefore, an efficient electrolyte
purification system (such as crystallization copper removal, electrowinning impurity removal, solvent extraction,
ion exchange, etc.) is crucial for maintaining high-quality electrolytic copper production.
Additive Function and Residues: To achieve a smooth and lustrous deposit layer, trace amounts of organic additives
(e.g., gelatin, thiourea) and inorganic additives (e.g., Cl⁻) are often added. These additives or their decomposition
products may be trace-level impurities in the copper deposit layer, affecting copper purity (e.g., increasing carbon,
sulfur, or nitrogen content) or microstructure. Precise control of their types and concentrations is critical.
Conclusion: Composition Determines Quality, Structure Determines Performance
The composition of electrolytic copper is far from a simple list of elements. It is:
The pinnacle of copper purity (>99.99%);
Extreme control of key impurity elements at the ppm/ppb level, backed by stringent standards (LME, GB/T 467,
ASTM B115, etc.) and processes;
A physical structure characterized by dense, uniform, defect-free microcrystalline grains;
A comprehensive quality assurance system spanning premium anode plates, precise electrolytic control, efficient
purification, and non-destructive post-processing.
It is this almost obsessive pursuit of “composition” that endows electrolytic copper with unparalleled electrical
conductivity, thermal conductivity, mechanical properties, and machinability, making it the core foundational
material supporting efficient power transmission in modern electrical networks, ensuring reliable operation of
precision electronic components, and driving continuous innovation in high-end equipment manufacturing.
Choosing truly high-quality electrolytic copper fundamentally means choosing a deep understanding and
strict control of its “composition.”