The average Book of Shadows that any serious Witch keeps as a record of his or her spells, experiments, daily activities, recipes and the like is not and should never be confused with or called a 'grimoire'. The primary difference is in the content. A Book of Shadows is more like a journal/lab manual/notebook that contains a plethora of information and accumulated knowledge the practicing Witch has acquired. A grimoire on the other hand is primarily focused on containing the procedures for spells alone.
The oldest known grimoires date back to the 13th century and primarily contain translations of older texts from Jewish mysticism and ancient Greek magical writings. Most of the spells contained within them deal with the instructions on the correct methods to call up Demons. The magicians that created and used these grimoires were concerned with the making of packs or deals with these dark spirits for the purpose of gaining power or wealth.
The word itself comes through the Old French from a Latin base. It means basically a 'grammar' book that defines the proper order of a language. With literacy a well controlled commodity in the medieval period. Any non-ecclesiastical writing was thereby 'suspect' and through this persecution of any 'unauthorized' source, the connotations of Dark Magic were given to these books. This was, they said, because the majority of the spells in the 'magic' grimoires dealt with the summoning and dealings with Demons and Angels by man instead of the priesthood.
Many of these old grimoires contained quite accurate astrological and astronomical calculations and events that conflicted with the Earth-centric view promoted by the Roman Church. This too, was a reason the 'Book of Enoch' was banned by the founders of the church at the Councils of Nicea even though it was supposedly written by one of their own prophets. Nor did it matter that the 'Lemegeton' alleged to the Old Testament Ruler, Solomon, was condemned though it gave instruction on both Black and White magic.
Grimoires saw a rise in popularity during the 15th through 17th Centuries. During this period the Protestant Movement rebelled and drew away from the 'Official Church'. This was alongside a variety of 'Satanic' and 'Heretical' systems that paralleled the old ways in 'blasphemous' parody.
In the modern age of Witchcraft and Magic the definitions of Grimoire and Book of Shadows has been often confused. As is usual, the majority of the blame is due to the over-imaginative tendencies of Hollywood scriptwriters. You may create your own Grimoire that contains just the instructions of your spells. As a Craft Tool the aesthetics of 'the book' included in your ritual has a positive effect. Part of the creation of a Grimoire, even of purely harmonious spells, is that you write it by hand. This additional vibrational connection to your spells has a positive effect on your spell work.
There are a fair number of the ancient grimoires that have survived through time. The Greater and Lesser Keys of Solomon, Cornelius Agrippa's 'Libri tres de occulta philosophia' or the 'Book of the Sacred Magic of Abra-Melin the Mage' are well known to modern literature. The new Grimoires of today have passed out of the dark stereotype of Dark Magic and are being produced for many paths of Magic.
A Grimoire is designed to teach you knowledge like a textbook. The Book of Shadows, being your daily record of your work and experiences, is more like a filing cabinet than a suitcase. It is where you keep track of the knowledge you have learned. Make them well and use them wisely.