The diagram above shows the relative abundances of the elements. Elements Li (Lithium), Be (Beryllium) and B (Boron) stand out. Theoretically, they are supposed to be more abundant than C (Carbon) but they are not. The smaller the atomic number (number of protons) the more abundant the element is supposed to be. This anomaly can be attributed to the relative instability of Lithium having 3 protons in the nucleus (Carbon has 6 protons). Leaving this anomaly aside, the more difficult puzzle is that the amount of Lithium in our galaxy is more than the expected amount based on the original Lithium formation after the Big Bang and the fragility of Lithium.
“Lithium is extremely fragile with just three protons in its nucleus and a very loosely-held outer electron, so it’s easy to destroy in stars and very easy to ionize (and, therefore, to miss) when we look for it astronomically. But it’s preserved in asteroids and comets.” 
I learned from Ethan Siegel’s article  that a team of researchers, led by astrophysicist Sumner Starrfield of Arizona State University, has combined theory with both observations and laboratory studies and determined that a class of stellar explosions, called classical novae, are responsible for most of the lithium in our galaxy and solar system. 
“The formation of the universe, commonly referred to as the “Big Bang,” primarily formed the elements hydrogen, helium and a little lithium. All the other chemical elements, including the majority of lithium, are formed in stars.
Classical novae are a class of stars consisting of a white dwarf (a stellar remnant with the mass of the sun but the size of Earth) and a larger star in close orbit around the white dwarf.
Gas falls from the larger star onto the white dwarf, and when enough gas has accumulated on the white dwarf, an explosion, or nova, occurs. There are about 50 explosions per year in our galaxy and the brightest ones in the night sky are observed by astronomers worldwide.” 
 Lithium Mystery Solved: It is exploding stars, not the Big Bang or Cosmic Rays