2025 could be the year we see a number of ultra-thin smartphones hit the market. Samsung has teased the Galaxy S25 Edge, which could launch in April. Meanwhile, Apple is expected to announce the iPhone 17 Air later this year.

But a lesser-known brand can surpass both the "giants" Apple and Samsung.

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Spark Slim is super thin but has a "huge" battery. Photo: Gizmochina

Tecno - a brand from China - has just introduced Spark Slim, a super-thin smartphone concept that still has a "huge" battery capacity at the MWC 2025 Mobile Exhibition taking place in Barcelona (Spain).

The Spark Slim is just 5.75mm thick, making it the world's thinnest phone, according to Tecno. The company says it has prioritized both durability and weight, using recycled aluminum alongside a unibody stainless steel frame.

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Spark Slim smartphone model with super thin design. Photo: Gizmochina

Despite its thinness, the Spark Slim is still equipped with a 5,200mAh battery, which is even larger than the battery equipped on the Galaxy S25 Ultra.

The ultra-slim smartphone features a 6.78-inch curved AMOLED display with 1.5K resolution and a 144Hz refresh rate. The company claims the display can reach a maximum brightness of 4,500 nits.

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Spark Slim at MWC 2025. Photo: Gizmochina

Inside, the device uses an 8-core processor, although Tecno has not revealed exactly which chip. The battery is only 4.04mm thick but supports 45W fast charging, and although the camera cluster is slightly protruding, the overall design of the Spark Slim is still very neat.

The Spark Slim has a 50MP dual camera system on the back, while the front uses a 13MP selfie camera. The pill-shaped camera cluster is horizontal, but instead of placing the sensors in the center as usual, the two lenses are arranged on the left and right sides. The light strip design around the camera helps the Spark Slim increase its eye-catching appearance.

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Spark Slim's horizontal pill-shaped rear camera cluster design. Photo: Gizmochina

Tecno has not announced the price, versions or other information.

At 5.75mm thick, the Spark Slim is quite an engineering feat, especially when compared to its rivals. The Galaxy S25 Edge, for example, is expected to be around 6mm thick and pack a 4,000mAh battery – significantly smaller.

Meanwhile, the iPhone 17 Air expected to launch later this year will be about 5.5mm thin, but the battery will certainly not be as large as the Spark Slim.

Hands-on with the Spark Slim concept at MWC 2025. Source: Gizmochina

The problem is that the Spark Slim is just a concept. There’s no official release date yet, and despite a demo at MWC, it’s highly unlikely the Spark Slim will ever hit the market.

Last year, Tecno also showed off a super-thin tri-fold phone, but it has yet to hit store shelves.

Tecno's Secret

How did Tecno manage to fit such a large battery into such a slim device? The answer lies in silicon-carbon battery technology.

This battery has a higher energy density in a more compact design, giving the device impressive battery life without increasing thickness.

Previously, the OnePlus 13 also applied similar technology to cram a 6,000mAh battery into a thin and light design.

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