Starting From heartsteel you gain ALOT of HP at start of game. As long as you keep fightning you gain more and more HP. Thanks to heartsteel your Passive+Grasp+Heartsteel+Deads Men Plate let you deal incredible ammount of damage. In late thanks to that you can literally eat 1/2hp of adc or other mage in one AA

Demonic Embace is whats you need as Akali the most. AP. Thanks to passive the more HP you gain fro hearsteel the more AP you get. Maybe its not spectacular ammount of AP but with this item you allready strong enough to 1v1 almost everyone.

Dead's Men Plate. Not only gives you great portion of Armor and health it also gives you extra dmg and mobility to catch your opponent. Its perfect combination to rest of your kit. In teamfight you can use it several times.

You can think why Abyssal Mask doing here. In almost every match you need some MR. This item not only gives you 60MR some HP and Ability haste but also have perfect passive for assasing going tank. Reduce enemy MR. And its scales with your HP! That means you have ap penetration without buing ap items. Thats insane. And coz you are in center of fight you gain up to 105 MR in one item

Ill dont speak alot about boots. Alot of AD enemies? Better steelcaps. But Mercuries is my favorite coz of tenacity. No CC? Socerers to more dmg. Thats all

Last item is situational so take what you need :)

Tank Akali playstyle is basicly the same as normal akali so if you want guide for laning phase etc just read some high-elo players guides on mobafire. See ya :D