Hmmm... this question would've been a tricky one. But the way i've been brought up influences the way i think. I am a muslim who DOES believe in a god. I therefore belive that lyying is not acceptable, but as a muslim i also believe in equility to all- male and female have equal rights.
In this case your husband has been taking advantage of his sex, he has been physically harming you and therefore you have the right to report him to police. A man cannot go about bossing and ordering his wife, he must not harm a wife in anyway (in your case he was harming you in both ways- physically and mentally). You did the right thing reporting him to the police but this is the but were you went wrong, you lied! Now i am not sure exactly what you told the police but if you told them he slapped you then you weren't lyying- because he did! But if you told them he had slapped you just before they arrived, then i'm afraid youwere lyying...
Lyying (as my grandmother explained to me) is one of the worst sins you can commit, one should tell the truth even if his life depended on it- now i know (we as humans) we aren't perfect, everyone has lied atleast once in there life, but tryying to recover the lost truth is a thing quite a few people do- in islam you would get sawaab (rewards) for this, but if you're not a muslim and you don't believe in that you still get a great feeling when you feel proud and honest.
There is a story i was told when i was younger about a saint. This saint was 14-years-old at the time (then he wasn't a saint). He was uneducated and understood the power of knowledge, he wanted to learn and become educated.He asked his mother and his mother gave him the only money she had. She sewed a little pocket on the underarm of his shirt for the money, then the boy parted of to the city with a group of people (a caravan) to learn.
It was on their way they were stopped by theives and robbed. the leader of the 'gang' came to this boy and asked him "where is your money". The boy replied honeslty and gave he exact location of his money. At first the man looked in amazement then he laughed "you not meant to tell me little boy! yuou know very little of this world!" the boy replied back i was honest. The man looked back in amazement, then this child explained the power of truth and how you should always be honest- the man imediately converted to islam and with the saints help managed to give all stolen goods back to the original owners! The 'gang' leader now became one of the most respected...
So thats how the story goes... Eventually things get put back together properly and you get respect!
Now back to your case- You can work 'around' your situation you should just tell them that this man (your husband) was causing you mental and physical harm! not on the date you specified obviously, but you can explain how he had caused you emotional distress, remember it's best to tell the truth now or else you'll have to continue lyying (and for how long will you be able to keep it up?).
Telling the truth is not a sin, you should always tell the truth (and even if you do lie- remeber it's not the end of the world, you can put things right)
I believe your husband does not have the values and the decency to be a husband if he has done what you have stated. But men change, he may understand he was wrong and he had no right to slap you.
I shall pray for your matters to easen up