"Science and science fiction, how do you even distinguish the two?"
- Jerry Pournelle

John W. Campbell used it in The Derelicts of Ganymede:

"...Get your stuff together and pile it in Lifeboat Seven, that'll be whole, and it's the biggest...

Duke Stetson pulled the releasing lever. Automatic doors opened, and a powerful spring gear drove the little twenty-foot ship clear of the gleaming monster.

Eando Binder used this phrase in Murder on the Asteroid in 1933:

In the wall nearest the hull was an air seal. He opened this. In the tiny chamber revealed rested a small ellipsoid metal object with a bulge of steel-glass on its top surface — the “life boat.”

Due to the constant dangers of meteors in space which might at any moment crash through an ether boat, each space vehicle carried one or more of the life boats. They were simply little one-man ether boats, miniature models of the larger craft, equipped with small but efficient rocket motors. If for any reason the larger boat became unmanageable, damaged, or useless as a vehicle, the passenger could then embark in the life boat and propel himself within reach of rescue. Each life boat was equipped with a radio. They also carried food, oxygen, and heating apparatus.

Hanson, holding the little man in his arms, smirked as he saw the dull metal ellipsoid boat, for it entered his plans of the moment. On its side was emblazoned the same number as was on the outside hull of the bigger boat — P-322-M-505...

Stooping, the fat man grasped the life boat by two of its many rocket tubes, raised it to his chest, and pushed it away from him forcefully. He knew that the gravitation of the asteroid was so small that it would fail to draw back again the little craft as it shot away from him like a blunt bullet.

('Murder on the Asteroid' by Eando Binder)

But before the little object passed out of view altogether, a ghastly white face with wide, fearful eyes appeared in the glass bulge and looked back to Hanson with a pitiful expression of horrible despair,

Hanson began to laugh then, and laughed insanely till he once again took off the suit in the ether boat.

“Mine, all mine!” he shouted, waving an arm to include all the visible topography. "He didn’t deserve any of it, the little rat—and now it's all mine!”

Here's another great graphic and text usage from Castaways on Deimos (1933) by J. Harvey Haggard:

('Castaways on Deimos' (1933) by J. Harvey Haggard)

Nevertheless, directly after the liner had careened drunkenly in space, an order was given through a megaphone — connected with a speaker in every cabin — for the passengers to man the lifeboats and prepare to leave the ship. While the passengers tumbled excitedly from their cabins, a continuous S. O. S. went streaking through the ether from a key beneath the finger of a capable radio sender.

Due to the efficiency of the officers of the Tuetonia the passengers boarded the many lifeboats in the side walls of the vessel with comparative orderliness. As each tiny dart-shaped lifeboat was filled with human occupants an automatic device closed an airlock, leaving the spindly tadpole of a lifeboat in a tiny closed compartment against the ship’s hull. Then a large section of the hull fell away, - also operated by automatic control, and the tiny lifeboat slid down a short runway to dart into the fiery storm of meteorites, heading swiftly out toward space — and to escape.

Doc Smith used this phrase just a year later in Triplanetary:

Through the airlock, down through several levels of passenger's quarters they hurried, and into a lifeboat.

Compare this very early use of the concept with a more famous descendant, the escape pod from George Lucas' 1976 story Star Wars.